Image-Guided Percutaneous Ablation for Primary and Metastatic Tumors

Image-guided percutaneous ablation methods have been further developed during the recent two decades and have transformed the minimally invasive and precision features of treatment options targeting primary and metastatic tumors. They work by percutaneously introducing applicators to precisely destroy a tumor and offer much lower risks than conventional methods. There are usually shorter recovery periods, less bleeding, and more preservation of organ parenchyma, expanding the treatment options of patients with cancer who may not be eligible for resection. Image-guided ablation techniques are currently utilized for the treatment of primary and metastatic tumors in various organs including the liver, pancreas, kidneys, thyroid and parathyroid, prostate, lung, bone, and soft tissue. This article provides a brief review of the various imaging modalities and available ablation techniques and discusses their applications and associated complications in various organs.


Introduction
Image-guided percutaneous ablation is defined as the process of percutaneously introducing needlelike applicators to destroy or shrink tumors in a controlled and targeted fashion under image guidance. This approach is a well-established minimally invasive practice for primary and metastatic tumors [1,2]. The advent of image-guided percutaneous ablation along with transarterial therapies has allowed interventional radiologists to not [17]. Other ways to guide percutaneous ablation devices is through the use of lipiodol or radiopaque beads. These are sometimes used in transarterial chemoembolization and can enhance intraprocedural imaging guidance by their ability to be visualized with fluoroscopy or CT [20,21]. Other ways to guide percutaneous ablation devices is via pre-ablation embolization of lesions using lipiodol or radiopaque beads. These are used in transarterial chemoembolization and can enhance intraprocedural imaging guidance by their ability to be visualized by fluoroscopy or CT [20,21].

MRI
Magnetic resonance imaging (MRI) is less frequently used than US or CT but is useful in that it uses no ionizing radiation, provides a high contrast resolution between soft tissues, displays small tumors with increased sensitivity, allows for imaging in any orientation and on any plane, monitors thermal effects, and can be combined with diffusion-weighted imaging or MRI contrast agents to visualize more difficult lesions [11]. The primary advantage of MRI guidance for tumor ablation, however, lies in its unique thermal sensitivity that allows online monitoring of the progress of ablation. The main disadvantages of MRI use include the lack of MR compatible tools, closed MRI not having real-time guidance, a relatively complicated operation, susceptibility to artifacts, and high cost [11].

Physics and Mechanism of Action of Percutaneous Ablation Devices
The tumor ablation techniques are divided into chemical ablation, thermal ablation, irreversible electroporation, or external-energy-delivery-based ablation ( Figure 1). Chemical ablation includes nonenergy-based ablation techniques such as intratumoral ethanol and acetic acid injection that cause coagulation necrosis leading to tumor ablation [1,22,23]. Thermal ablation includes modalities that destroy tissue via heat or cold and include radiofrequency ablation (RFA), cryoablation, microwave ablation (MWA), and laser ablation. External-energy-delivery-based ablation includes high-intensity frequency ultrasound (HIFU) and histotripsy ( Figure 1). The advantages and disadvantages of the common ablation techniques are summarized in Table 1.    Figure 2) works by delivering radiofrequency waves in the 375-500 kHz range to an area surrounding a generator-coupled electrode, causing an oscillating electric field that creates frictional energy by electron collision. This collision generates heat that leads to eventual tumor destruction by coagulation necrosis from temperatures above 60 • C [19,24,25]. Design of a bipolar RFA system, in which electrical current is delivered through an electrode that functions as both anode and cathode [26]; bi-polar electrodes obviate the need for grounding pads; (B) Representative example of RFA used to target a lesion in right middle lobe of a lung.

Microwave Ablation
MWA ( Figure 3) uses microwave energy in the 300-3000 MHz range from an antenna, creating oscillation of ions in the target [19]. This oscillation creates heat and results in coagulative necrosis. This technique allows for faster ablation times, larger ablation zones, and a reduced heat sink effect compared to RFA [27,28].

Cryoablation
Cryoablation ( Figure 4) destroys tumors by applying freezing temperatures or alternating freeze-thaw cycles [29]. This technique works by utilizing the Joule-Thomson effect by which certain gases such as nitrogen, nitrous oxide, or argon drop in temperature when going from high pressure to low pressure [24,30]. Once the target region reaches temperature of −40 °C, ice crystals form in the extracellular space that leads to increased tonicity and osmotic damage to cells in the area [24,31,32]. Eventually, intracellular ice forms, rupturing the plasma and organelle membranes, followed by indirect cell death by thrombosis of damaged blood vessels that lead to ischemia and inflammation [24,33]. Design of a bipolar RFA system, in which electrical current is delivered through an electrode that functions as both anode and cathode [26]; bi-polar electrodes obviate the need for grounding pads; (B) Representative example of RFA used to target a lesion in right middle lobe of a lung. Figure 3) uses microwave energy in the 300-3000 MHz range from an antenna, creating oscillation of ions in the target [19]. This oscillation creates heat and results in coagulative necrosis. This technique allows for faster ablation times, larger ablation zones, and a reduced heat sink effect compared to RFA [27,28]. Design of a bipolar RFA system, in which electrical current is delivered through an electrode that functions as both anode and cathode [26]; bi-polar electrodes obviate the need for grounding pads; (B) Representative example of RFA used to target a lesion in right middle lobe of a lung.

Microwave Ablation
MWA ( Figure 3) uses microwave energy in the 300-3000 MHz range from an antenna, creating oscillation of ions in the target [19]. This oscillation creates heat and results in coagulative necrosis. This technique allows for faster ablation times, larger ablation zones, and a reduced heat sink effect compared to RFA [27,28].

Cryoablation
Cryoablation ( Figure 4) destroys tumors by applying freezing temperatures or alternating freeze-thaw cycles [29]. This technique works by utilizing the Joule-Thomson effect by which certain gases such as nitrogen, nitrous oxide, or argon drop in temperature when going from high pressure to low pressure [24,30]. Once the target region reaches temperature of −40 °C, ice crystals form in the extracellular space that leads to increased tonicity and osmotic damage to cells in the area [24,31,32]. Eventually, intracellular ice forms, rupturing the plasma and organelle membranes, followed by indirect cell death by thrombosis of damaged blood vessels that lead to ischemia and inflammation [24,33].

Cryoablation
Cryoablation ( Figure 4) destroys tumors by applying freezing temperatures or alternating freeze-thaw cycles [29]. This technique works by utilizing the Joule-Thomson effect by which certain gases such as nitrogen, nitrous oxide, or argon drop in temperature when going from high pressure to low pressure [24,30]. Once the target region reaches temperature of −40 • C, ice crystals form in the extracellular space that leads to increased tonicity and osmotic damage to cells in the area [24,31,32]. Eventually, intracellular ice forms, rupturing the plasma and organelle membranes, followed by indirect cell death by thrombosis of damaged blood vessels that lead to ischemia and inflammation [24,33].

Irreversible Electroporation
IRE ( Figure 5) is a nonthermal ablation modality that causes cell death through repeated short-duration high-voltage electrical pulses, leading to ruptured cellular membranes and irreversible cell death [34,35]. IRE differs from the thermal modalities in that it is not affected by the heat sink effect [1].

Laser Ablation
Laser ablation uses light energy to precisely heat a tumor electromagnetically and cause coagulative necrosis. It is a flexible technique that can be conveniently coupled through optical fibers that are MR compatible, but the small ablation zones require multiple placements [19]. Furthermore, laser ablation can have limited energy penetration as most body tissues absorb and scatter light [36].  Figure 5) is a nonthermal ablation modality that causes cell death through repeated short-duration high-voltage electrical pulses, leading to ruptured cellular membranes and irreversible cell death [34,35]. IRE differs from the thermal modalities in that it is not affected by the heat sink effect [1].

Irreversible Electroporation
IRE ( Figure 5) is a nonthermal ablation modality that causes cell death through repeated short-duration high-voltage electrical pulses, leading to ruptured cellular membranes and irreversible cell death [34,35]. IRE differs from the thermal modalities in that it is not affected by the heat sink effect [1].

Laser Ablation
Laser ablation uses light energy to precisely heat a tumor electromagnetically and cause coagulative necrosis. It is a flexible technique that can be conveniently coupled through optical fibers that are MR compatible, but the small ablation zones require multiple placements [19]. Furthermore, laser ablation can have limited energy penetration as most body tissues absorb and scatter light [36].

Laser Ablation
Laser ablation uses light energy to precisely heat a tumor electromagnetically and cause coagulative necrosis. It is a flexible technique that can be conveniently coupled through optical fibers that are MR compatible, but the small ablation zones require multiple placements [19]. Furthermore, laser ablation can have limited energy penetration as most body tissues absorb and scatter light [36].

High-Intensity Frequency Ultrasound
HIFU ( Figure 6) is a noninvasive thermal ablation technique that causes coagulation necrosis by delivering high-intensity ultrasound waves onto a focal area [37]. The sources of ultrasound are often placed extracorporeally or rectally without the need for the transcutaneous insertion of probes.

High-Intensity Frequency Ultrasound
HIFU ( Figure 6) is a noninvasive thermal ablation technique that causes coagulation necrosis by delivering high-intensity ultrasound waves onto a focal area [37]. The sources of ultrasound are often placed extracorporeally or rectally without the need for the transcutaneous insertion of probes. Figure 6. Schematic presentation of high-intensity frequency ultrasound for ablation of a prostate tumor. The extracorporeal transducer generates high-intensity ultrasound to carry and propagate energy onto a focused area deep within tissue media. Temperatures are raised to a level that is sufficient for thermotherapeutic effects, resulting in coagulation necrosis [38,39].

Histotripsy
Histotripsy ( Figure 7) is a noninvasive ablation technique based on ultrasound but is nonthermal. It uses focused ultrasound waves to mechanically destroy tissue through cavitation, causing minimal damage to surrounding tissue [40]. It works by using pulsed sound waves to create "bubble clouds" from gases naturally occurring in the target. These bubbles form and collapse quickly, leading to mechanical force-based destruction of the tissue [41]. Like HIFU, a focused transducer is used to generate and focus ultrasound to the tumor, but it instead causes mechanical damage without thermal coagulation via short, intense acoustic pulses that create dense energetic "bubble clouds" in the tissue media. These bubbles rapidly expand and collapse to mechanically disintegrate tissue [42]. The extracorporeal transducer generates high-intensity ultrasound to carry and propagate energy onto a focused area deep within tissue media. Temperatures are raised to a level that is sufficient for thermotherapeutic effects, resulting in coagulation necrosis [38,39].

Histotripsy
Histotripsy ( Figure 7) is a noninvasive ablation technique based on ultrasound but is nonthermal. It uses focused ultrasound waves to mechanically destroy tissue through cavitation, causing minimal damage to surrounding tissue [40]. It works by using pulsed sound waves to create "bubble clouds" from gases naturally occurring in the target. These bubbles form and collapse quickly, leading to mechanical force-based destruction of the tissue [41].

High-Intensity Frequency Ultrasound
HIFU ( Figure 6) is a noninvasive thermal ablation technique that causes coagulation necrosis by delivering high-intensity ultrasound waves onto a focal area [37]. The sources of ultrasound are often placed extracorporeally or rectally without the need for the transcutaneous insertion of probes. Figure 6. Schematic presentation of high-intensity frequency ultrasound for ablation of a prostate tumor. The extracorporeal transducer generates high-intensity ultrasound to carry and propagate energy onto a focused area deep within tissue media. Temperatures are raised to a level that is sufficient for thermotherapeutic effects, resulting in coagulation necrosis [38,39].

Histotripsy
Histotripsy ( Figure 7) is a noninvasive ablation technique based on ultrasound but is nonthermal. It uses focused ultrasound waves to mechanically destroy tissue through cavitation, causing minimal damage to surrounding tissue [40]. It works by using pulsed sound waves to create "bubble clouds" from gases naturally occurring in the target. These bubbles form and collapse quickly, leading to mechanical force-based destruction of the tissue [41]. Like HIFU, a focused transducer is used to generate and focus ultrasound to the tumor, but it instead causes mechanical damage without thermal coagulation via short, intense acoustic pulses that create dense energetic "bubble clouds" in the tissue media. These bubbles rapidly expand and collapse to mechanically disintegrate tissue [42]. Like HIFU, a focused transducer is used to generate and focus ultrasound to the tumor, but it instead causes mechanical damage without thermal coagulation via short, intense acoustic pulses that create dense energetic "bubble clouds" in the tissue media. These bubbles rapidly expand and collapse to mechanically disintegrate tissue [42].

Primary and Metastatic Liver Tumors
The preferred treatment option for localized hepatocellular carcinoma (HCC) is surgical resection. However, a proportion of patients are not candidates for surgery due to the extent of the tumor or underlying poor liver function [43]. Ablation for localized HCC is a viable treatment option in patients with nonresectable tumors who are not transplant candidates, especially in patients with no worse than Child-Turcotte-Pugh class A or B cirrhosis, or in transplant candidates as a form of bridging or downstaging therapy [44]. The 2022 Barcelona Clinic Liver Cancer guidelines now recommend ablation as the standard of treatment in patients with solitary HCC ≤ 2 cm without vascular invasion or extrahepatic spread, for which liver transplant is not feasible [45]. Multiple percutaneous ablation modalities are used in treating liver tumors with the main techniques being RFA and MWA. MWA has several theoretical advantages over RFA in that it can obtain shorter ablation times, multiple ablations can be performed simultaneously, it can reach higher intratumoral temperatures with larger ablation zones, its efficacy is not reduced by electrical impedance, and it is less susceptible to the heat sink effect [44,[46][47][48][49][50][51]. However, these advantages may make MWA more dangerous in injuring nearby structures [44,51,52]. Several randomized trials have been conducted to compare MWA versus RFA for HCC treatment, showing that MWA is comparable to RFA for HCC treatment in terms of safety and efficacy but has reduced local tumor progression and shorter ablation times (Table 2) [13,51,[53][54][55][56][57][58][59]. A case of a patient receiving MWA for a hepatic metastatic leiomyosarcoma in segment V is presented in Figure 8.
resection. However, a proportion of patients are not candidates for surgery due to the extent of the tumor or underlying poor liver function [43]. Ablation for localized HCC is a viable treatment option in patients with nonresectable tumors who are not transplant candidates, especially in patients with no worse than Child-Turcotte-Pugh class A or B cirrhosis, or in transplant candidates as a form of bridging or downstaging therapy [44]. The 2022 Barcelona Clinic Liver Cancer guidelines now recommend ablation as the standard of treatment in patients with solitary HCC ≤ 2 cm without vascular invasion or extrahepatic spread, for which liver transplant is not feasible [45]. Multiple percutaneous ablation modalities are used in treating liver tumors with the main techniques being RFA and MWA. MWA has several theoretical advantages over RFA in that it can obtain shorter ablation times, multiple ablations can be performed simultaneously, it can reach higher intratumoral temperatures with larger ablation zones, its efficacy is not reduced by electrical impedance, and it is less susceptible to the heat sink effect [44,[46][47][48][49][50][51]. However, these advantages may make MWA more dangerous in injuring nearby structures [44,51,52]. Several randomized trials have been conducted to compare MWA versus RFA for HCC treatment, showing that MWA is comparable to RFA for HCC treatment in terms of safety and efficacy but has reduced local tumor progression and shorter ablation times (Table 2) [13,51,[53][54][55][56][57][58][59]. A case of a patient receiving MWA for a hepatic metastatic leiomyosarcoma in segment V is presented in Figure 8.
Cryoablation can also be used in the treatment of HCC. While heat-based thermal ablation modalities are typically used in cirrhotic patients due to their lower rates of bleeding complications, cryoablation technology now includes thinner probes and helium-argon as a cryogen instead of liquid nitrogen [60][61][62][63]. Cryoablation is usually the preferred modality for hepatic tumors near vulnerable structures as it can produce smaller ablation zones, which can be monitored in real-time via intraprocedural CT [63,64]. Furthermore, cryoablation allows for neurolysis, making it suitable for subcapsular lesions or lesions close to the diaphragm. While the data comparing cryoablation to RFA for HCC is not as extensive as that between MWA and RFA, a randomized controlled trial and large population-based retrospective study found non-inferior results for cryoablation [63,65,66].  Cryoablation can also be used in the treatment of HCC. While heat-based thermal ablation modalities are typically used in cirrhotic patients due to their lower rates of bleeding complications, cryoablation technology now includes thinner probes and heliumargon as a cryogen instead of liquid nitrogen [60][61][62][63]. Cryoablation is usually the preferred Diagnostics 2022, 12, 1300 9 of 34 modality for hepatic tumors near vulnerable structures as it can produce smaller ablation zones, which can be monitored in real-time via intraprocedural CT [63,64]. Furthermore, cryoablation allows for neurolysis, making it suitable for subcapsular lesions or lesions close to the diaphragm. While the data comparing cryoablation to RFA for HCC is not as extensive as that between MWA and RFA, a randomized controlled trial and large population-based retrospective study found non-inferior results for cryoablation [63,65,66].
IRE is another modality that can be used in treating liver tumors, especially when close to adjacent major blood vessels or biliary ducts, as its not subjected to the heat sink effect. Results from clinical trials, and meta-analysis showed that IRE was effective and relatively safe ( Table 2) [67][68][69][70][71][72]. Figure 9 discusses the management of a patient with cirrhosis and HCC with both MWA and IRE. IRE is another modality that can be used in treating liver tumors, especially when close to adjacent major blood vessels or biliary ducts, as its not subjected to the heat sink effect. Results from clinical trials, and meta-analysis showed that IRE was effective and relatively safe ( Table 2) [67][68][69][70][71][72]. Figure 9 discusses the management of a patient with cirrhosis and HCC with both MWA and IRE. HIFU has been shown to be safe and effective with comparable outcomes to the other modalities [73][74][75][76][77][78]. A prospective comparative study revealed that HIFU was as safe and effective as RFA [79]. The new #HOPE4LIVER clinical trial is currently in the process of seeking regulatory approval to determine the efficacy of histotripsy for both primary and metastatic liver tumors.
Percutaneous ethanol or acetic acid injections are also sometimes used in resourcelimited settings but are not usually recommended if other modalities are available. However, the literature is inconsistent, and some studies show a comparable role of ethanol in small liver tumors [31,80,81]. (D) Four-month follow-up MRI showed complete response of the segment II HCC to MWA, but the two previously noted lesions (E) in the caudate lobe and segment VII progressed to LI-RADS 5. The patient underwent image-guided percutaneous ablation of these two lesions two months later, receiving (F) NanoKnife IRE for segment II/caudate and (G) MWA for segment VII lesion. (H) One-month follow-up MRI shows no residual tumor. The patient was transplanted two months later.
HIFU has been shown to be safe and effective with comparable outcomes to the other modalities [73][74][75][76][77][78]. A prospective comparative study revealed that HIFU was as safe and effective as RFA [79]. The new #HOPE4LIVER clinical trial is currently in the process of seeking regulatory approval to determine the efficacy of histotripsy for both primary and metastatic liver tumors.
Percutaneous ethanol or acetic acid injections are also sometimes used in resourcelimited settings but are not usually recommended if other modalities are available. However, the literature is inconsistent, and some studies show a comparable role of ethanol in small liver tumors [31,80,81]. While ablation is generally accepted as a safe alternative for unresectable liver tumors, various complications may occur, with hemorrhage being one of the most common complications in patients treated with thermal ablation [84]. A systematic review of 15,744 patients found that morality ranged from 0% to 0.88% with a pooled morality of 0.15% for RFA and 0.23% for MWA [85]. Major complication rates were 4.1% for RFA and 4.6% for MWA while minor complication rates were 5.9% for RFA and 5.7% for MWA [85]. Some of the common major complications noted were intraperitoneal hemorrhage, portal vein thrombosis, biloma, bile duct injury, and liver dysfunction [85]. With regard to cryoablation, there is a concern for an increased risk of bleeding due to the multiple cryoprobes without the ability to cauterize or coagulate vessels [84]. Furthermore, cryoablation runs the risk of cryoshock and parenchymal crack in the liver [84]. While IRE initially ran into the risk of cardiac toxicity and arrhythmias, the introduction of cardiac synchronization with IRE has made it a relatively safe choice for liver ablation [86]. Most of the complications of IRE are primarily due to electrode placement, and IRE appears to be safer than thermal ablation when adjacent to critical structures like the bile duct, as thermal ablation tends to lead to portal vein thrombosis, necrosis, and bilomas [86]. Moreover, most of the complications of IRE in liver ablation tend to be mild or transient, such as fever, local pain, abdominal distension, ascites, nausea, and vomiting [87]. In the case of HIFU, ablation of small liver tumors, even in patients with advanced cirrhosis, is relatively safe, but current challenges that are still being addressed are targeting tumors in difficult locations, such as the liver dome, structures near the rib cage, structures near large blood vessels or the heart, and structures adjacent to hollow viscera [88].

Renal Tumors
While the conventional treatment for renal cell carcinoma (RCC) has historically been radical nephrectomy, efforts to reduce the invasiveness, such as with nephron-sparing surgeries, have developed over the years [9,[89][90][91]. This change to less invasive procedures to preserve the renal parenchyma has also led to use of image-guided thermal ablations for renal tumors with promising outcomes in unresectable tumors [36,[92][93][94][95][96]. Current national comprehensive cancer network (NCCN) guidelines currently have ablative techniques as one of the primary treatment options for stage I-III kidney cancer [97].
A meta-analyses and multiple cohort studies have shown that RFA and cryoablation have comparable efficacy and safety profiles for renal masses [98][99][100][101][102][103]. However, cryoablation appears to have better outcomes in larger >3-4 cm tumors than RFA [103][104][105][106]. Figure 10 presents the use of cryoablation on a patient with a left renal mass. MWA has also been shown to result in promising outcomes in renal tumors. A retrospective analysis of T1N0M0 RCC showed that the outcome of CT-guided percutaneous MWA is comparable to RFA or cryoablation with regard to treatment response and is associated with less sedation and lower treatment times [107]. Several other studies have shown comparable therapeutic and renal function outcomes among MWA, RFA, and cryoablation (Table 3) [108,109].
Complications for renal tumor ablation include both injury to the kidney, as well as the surrounding structures, like the vasculature or urinary tract. Complications include hemorrhage, ureteral stricture, urine leakage, urinary tract infections, pneumothorax, nerve injury, skin burns, and needle tract seeding [110]. In a prospective study of 573 renal ablation procedures (254 RFA and 311 cryoablation) performed in 533 patients with 633 tumors, complications did not statistically differ between the two [101]. In the RFA group, 3.9% had nerve injury, 2.1% had urothelial stricture, and 1.2% had hemorrhage/vascular injury/anemia [101]. In the cryoablation group, 4.8% had hemorrhage/vascular injury/anemia, 2.6% had hematuria, 1% had pulmonary embolus, and 0.6% had nerve injury [101]. A retrospective study of 105 US-guided percutaneous MWA in 111 patients with renal tumors found a complication rate of 24.8% with major complications including two hydrothorax and one bowel injury, while the minor complications included microscopic hematuria, mild thermal injury to the psoas muscle, perirenal hematoma, diarrhea, abdominal distension, edema of the lower extremities, and thermal injury to the pelvicalyceal system [111]. Some ways to prevent complications include holding anticoagulants to prevent bleeding, hydrodissection to avoid thermal injury to adjacent structure, and pyeloperfusion to protect the ureter [112,113]. drothorax and one bowel injury, while the minor complications included microscopic hematuria, mild thermal injury to the psoas muscle, perirenal hematoma, diarrhea, abdominal distension, edema of the lower extremities, and thermal injury to the pelvicalyceal system [111]. Some ways to prevent complications include holding anticoagulants to prevent bleeding, hydrodissection to avoid thermal injury to adjacent structure, and pyeloperfusion to protect the ureter [112,113].

Pancreatic Tumors
Pancreatic cancer is the fourth leading cause of cancer-related death in the United States, and most patients are diagnosed with locally advanced or metastatic disease [114]. Current national guidelines recommend systemic therapy as the first-line treatment for unresectable pancreatic tumors [114]. However, most patients relapse, and chemotherapy is still associated with poor survival and complications [115]. Additionally, there are low rates of conversion surgery with R0 resections following systemic treatment [116]. Therefore, ablative techniques have emerged as an alternative adjuvant treatment for patients with pancreatic tumors, but they are mainly used as a consolidative treatment in stable tumors or as palliative care for tumors with persistent major vascular involvement [115,116]. The role of tumor ablation in pancreatic cancer is still understudied and there have been no completed trials that compare multiple ablation modalities [115,117]. Examples of the major ongoing trials are the "Pancreatic Locally Advanced Unresectable Cancer Ablation" (PELICAN) trial [118], which is an international multicentric superiority RCT investigating the effect of RFA in combination with chemotherapy in 228 patients across 16 centers in the Netherlands and four European centers, and the CROSSFIRE trial in the Netherlands, which compares the efficacy of IRE and chemotherapy (FOLFIRINOX) to the efficacy of FOLFIRINOX and stereotactic ablative radiotherapy (SABR) in 138 patients with nonresectable, non-metastasized, locally advanced pancreatic cancer (LAPC) [117].
The most used and studied ablative therapies for pancreatic cancer are RFA, IRE, and stereotactic body radiation therapy (SBRT) [117]. A recent systematic review screened 1037 articles published before 1 June 2014 and found 38 clinical studies with 1164 patients with LAPC, of which seven involved RFA, four involved IRE, 16 involved SBRT, five involved HIFU, two involved iodine-125, two involved iodine-125-cryosurgery, one involved photodynamic therapy, and one involved MWA [119]. The review found that all strategies seemed safe and feasible [119]. Of the modalities that had outcomes for postoperative-procedure-related morbidity and mortality, RFA had 4-22% and 0-11%, respectively, IRE had 9-15% and 0-4%, respectively, and SBRT had 0-25% and 0%, respectively [119]. Median survival for RFA, IRE, SBRT, and HIFU was 25.6, 20.2, 24.0, and 12.6 months, respectively [119]. Furthermore, the study found that IRE procedures were safer when done with a percutaneous approach than with an open approach [119]. Figure 11 describes the case of a patient with locally advanced pancreatic cancer who was treated with IRE. Another review that examined ablation treatments for pancreatic cancer from January 2010 to May 2020, found 36 articles that met the inclusion criteria, of which 18 were for RFA, three for MWA, 11 for IRE, and four for electrochemotherapy (ECT) [115]. The mean (range) overall survival was 23 months (9-30), 24.9 months (4.9-85) and 11.5 months for RFA, IRE, and ECT, respectively [115]. The major and minor mean complication rate was 1.9% and 20.2% for RFA, respectively, 8.5% and 8.6% for MWA, respectively, 1.5% and 15% (open vs. 29% percutaneously) for IRE, respectively, and 0% and 23.1% for ECT, respectively [115].
The main risks of ablation in the pancreas are due to the location of the pancreas. Unlike other solid organs, the pancreas both involves and is surrounded by many medium-to large-sized blood vessels such as the celiac and hepatic arteries, the portal vein, and the superior mesenteric and splenic vessels [120]. Common complications due to ablation include pancreatitis, pancreatic duct fistulas and leaks, and pseudocysts. For RFA, there appears to be a correlation between the temperature reached in the ablation and complications, which is why some authors suggest avoiding over 90 °C in ablation temperatures [121]. Common complications associated with RFA also tend to include pancreatic fistulas, portal thromboses, and pancreatitis [121]. While the data concerning MWA complications is more sparce, possible complications include mild pancreatitis, hyperamylasemia, pancreatic ascites, mild hemorrhage, and pseudocysts [121,122]. Possible complications for cryoablation include pancreatic and bile leak, gastrointestinal bleeding and obstruction, infection, and hemorrhage [122].

Primary and Metastatic Adrenal Tumors
While ablation has been primarily focused on treating malignancies in organs such as the liver and kidneys, ablation modalities have expanded to target both benign and malignant endocrine tumors, especially those of the thyroid, parathyroid, and adrenal glands, to address systemic endocrinopathy [123]. Adrenal tumors have an estimated Another review that examined ablation treatments for pancreatic cancer from January 2010 to May 2020, found 36 articles that met the inclusion criteria, of which 18 were for RFA, three for MWA, 11 for IRE, and four for electrochemotherapy (ECT) [115]. The mean (range) overall survival was 23 months (9-30), 24.9 months (4.9-85) and 11.5 months for RFA, IRE, and ECT, respectively [115]. The major and minor mean complication rate was 1.9% and 20.2% for RFA, respectively, 8.5% and 8.6% for MWA, respectively, 1.5% and 15% (open vs. 29% percutaneously) for IRE, respectively, and 0% and 23.1% for ECT, respectively [115].
The main risks of ablation in the pancreas are due to the location of the pancreas. Unlike other solid organs, the pancreas both involves and is surrounded by many mediumto large-sized blood vessels such as the celiac and hepatic arteries, the portal vein, and the superior mesenteric and splenic vessels [120]. Common complications due to ablation include pancreatitis, pancreatic duct fistulas and leaks, and pseudocysts. For RFA, there appears to be a correlation between the temperature reached in the ablation and complications, which is why some authors suggest avoiding over 90 • C in ablation temperatures [121]. Common complications associated with RFA also tend to include pancreatic fistulas, portal thromboses, and pancreatitis [121]. While the data concerning MWA complications is more sparce, possible complications include mild pancreatitis, hyperamylasemia, pancreatic ascites, mild hemorrhage, and pseudocysts [121,122]. Possible complications for cryoablation include pancreatic and bile leak, gastrointestinal bleeding and obstruction, infection, and hemorrhage [122].

Primary and Metastatic Adrenal Tumors
While ablation has been primarily focused on treating malignancies in organs such as the liver and kidneys, ablation modalities have expanded to target both benign and malignant endocrine tumors, especially those of the thyroid, parathyroid, and adrenal glands, to address systemic endocrinopathy [123]. Adrenal tumors have an estimated prevalence of 3-10% in those aged > 50 years and many are found as "incidentalomas" on abdominal imaging, for which most have no clinical significance [123][124][125]. Surgery remains the recommended treatment of choice for adrenal tumors that have clinical significance [123]. Ablation of these tumors is beginning to garner attention in both primary and metastatic settings due to its minimally invasive profile and its ability to be used in patients who are unfit for surgery. Furthermore, the expansion of ablation technology has allowed for further precision to target diseased tissue and preserve the adrenal parenchyma. This expansion can also be seen in new methods, such as the recent novel protocol of singlesession CT-guided percutaneous MWA without pre-procedure adrenergic blockade that showed successful ablation, symptomatic improvement, and no residual tumor at 3-month follow-up in two patients with symptomatic Cushing syndrome who were not surgical candidates [126]. However, the data on clinical efficacy is still rather limited.
Most of the evidence of ablation therapy for adrenal tumors comes from small observational studies and case series that use RFA, MWA, and cryoablation. Figure 12 demonstrates a case of an adrenal tumor treated with cryoablation while still limited, the data is encouraging for ablation. In a recent review, Donlon and Dennedy found that unilateral aldosterone-producing adenomas (APA) and cortisol-secreting adenomas cured endocrinopathy with RFA and MWA for 75-100% of cases after a single ablation and 100% after repeated ablation [123]. They also found that thermal ablation leads to the promising resolution of hypertension following a thermal ablation for APA, similar to unilateral adrenalectomy [123]. Furthermore, this review also found promising results for RFA and MWA in metastatic adrenal tumors, in which the presence of residual tumor following ablation was seen in <25% of cases with <25% recurrence rates [123]. RFA has also shown to be promising in patients with severe adrenocorticotropic hormone (ACTH)-dependent Cushing syndrome for which bilateral adrenalectomy is not a suitable option [123,127]. A small case-series showed that all five patients who underwent bilateral RFA under CT-guidance had technical success with a resolution of their hypercortisolemia [127].
prevalence of 3-10% in those aged > 50 years and many are found as "incidentalomas" on abdominal imaging, for which most have no clinical significance [123][124][125]. Surgery remains the recommended treatment of choice for adrenal tumors that have clinical significance [123]. Ablation of these tumors is beginning to garner attention in both primary and metastatic settings due to its minimally invasive profile and its ability to be used in patients who are unfit for surgery. Furthermore, the expansion of ablation technology has allowed for further precision to target diseased tissue and preserve the adrenal parenchyma. This expansion can also be seen in new methods, such as the recent novel protocol of single-session CT-guided percutaneous MWA without pre-procedure adrenergic blockade that showed successful ablation, symptomatic improvement, and no residual tumor at 3-month follow-up in two patients with symptomatic Cushing syndrome who were not surgical candidates [126]. However, the data on clinical efficacy is still rather limited.
Most of the evidence of ablation therapy for adrenal tumors comes from small observational studies and case series that use RFA, MWA, and cryoablation. Figure 12 demonstrates a case of an adrenal tumor treated with cryoablation while still limited, the data is encouraging for ablation. In a recent review, Donlon and Dennedy found that unilateral aldosterone-producing adenomas (APA) and cortisol-secreting adenomas cured endocrinopathy with RFA and MWA for 75-100% of cases after a single ablation and 100% after repeated ablation [123]. They also found that thermal ablation leads to the promising resolution of hypertension following a thermal ablation for APA, similar to unilateral adrenalectomy [123]. Furthermore, this review also found promising results for RFA and MWA in metastatic adrenal tumors, in which the presence of residual tumor following ablation was seen in <25% of cases with <25% recurrence rates [123]. RFA has also shown to be promising in patients with severe adrenocorticotropic hormone (ACTH)-dependent Cushing syndrome for which bilateral adrenalectomy is not a suitable option [123,127]. A small case-series showed that all five patients who underwent bilateral RFA under CTguidance had technical success with a resolution of their hypercortisolemia [127]. During cryoablation the entire mass (white arrow) demonstrates lowered HU as its density decreases during freezing. The "ice-ball" is difficult to visualize in fatty regions because its CT density is very close to that of fat. The peri-adrenal fat becomes "fuzzy" indicating extension of the "ice-ball" around the adrenal mass.
A recent 2021 meta-analysis studied the efficacy and safety of image-guided percutaneous ablation of adrenal metastases [128]. Of the 959 patients undergoing RFA, MWA, cryoablation, and ethanol injections, or some mixture of these modalities, they found a pooled 1-year local control rate of 80%, a pooled 1-year overall survival of 77%, an overall rate of severe adverse events (CTCAE grade 3 or higher) of 16.1%, and an overall rate of During cryoablation the entire mass (white arrow) demonstrates lowered HU as its density decreases during freezing. The "ice-ball" is difficult to visualize in fatty regions because its CT density is very close to that of fat. The peri-adrenal fat becomes "fuzzy" indicating extension of the "ice-ball" around the adrenal mass.
A recent 2021 meta-analysis studied the efficacy and safety of image-guided percutaneous ablation of adrenal metastases [128]. Of the 959 patients undergoing RFA, MWA, cryoablation, and ethanol injections, or some mixture of these modalities, they found a pooled 1-year local control rate of 80%, a pooled 1-year overall survival of 77%, an overall rate of severe adverse events (CTCAE grade 3 or higher) of 16.1%, and an overall rate of low-grade adverse events (CTCAE grade 2 or lower) of 32.6% [128].
Ablation also shows promise in metastatic pheochromocytomas and paragangliomas (PPGLI), which are neuroendocrine tumors [129]. A retrospective analysis performed at the Mayo Clinic analyzed 31 patients with metastatic PPGL and 123 lesions, 42 of which were treated with RFA, 23 with cryoablation, and four with PEI, from 1999 to 2017 [129]. Radiographic local control was obtained in 86% of lesions and 92% of the procedures led to improvement in metastasis-related pain or symptoms of catecholamine excess [129]. A total of 67% of the procedures had no complications, and 14%, 14%, 2%, and 2% of the procedures had Clavien-Dindo Grade I, II, IV, and V complications, respectively [129].
The complications and risks of adrenal ablation include hemorrhage, infection, and hypertensive crisis [130]. Thermal ablation modalities can lead to injury to surrounding organs like the kidneys, pancreas, and lungs. Hormonal activation, leading to stroke or cardiac syndromes from catecholamine release, and tumor seeding of the ablation probe tract are other risks of ablation [124,130].

Thyroid and Parathyroid Tumors
While surgery is the main treatment option for patients with thyroid tumors, a growing number of studies have reported the safety and effectiveness of thermal ablations for thyroid tumors [131][132][133][134][135][136][137][138][139][140]. Several meta-analyses have also shown that thermal ablations are effective and safe alternatives [141][142][143][144] for primary and secondary hyperparathyroidism, primarily caused by parathyroid adenomas. Table 4 summarizes comparative studies on the various ablation modalities used, showing that RFA typically leads to superior volume reduction rates (VRR) for thyroid nodules when compared to other ablation modalities like MWA and laser ablation (LA). Comparative results of ablation modalities for parathyroid tumors are limited. Overall, ablation of thyroid and parathyroid tumors is becoming a more well-accepted alternative to surgery due to its minimal invasiveness and shorter recovery time [135,145]. Figure 13 discusses a representative case of a thyroid nodule ablation. While ablation is generally safe for thyroid and parathyroid tumors, there are several risks and complications that may arise. The typical ones include hoarseness, hematomas, hypothyroidism, nerve injuries (especially to the laryngeal nerve), nodule rupture, skin burns, and hypocalcemia [156,157]. While ablation is generally safe for thyroid and parathyroid tumors, there are several risks and complications that may arise. The typical ones include hoarseness, hematomas, hypothyroidism, nerve injuries (especially to the laryngeal nerve), nodule rupture, skin burns, and hypocalcemia [156,157].

Prostate Tumors
The recent increase in screening measures has led to the detection of prostate cancers at earlier stages, calling into question the current standard treatments of radical prostatectomy, high dose prostate brachytherapy, and external beam radiation therapy that target the wholegland prostate and reduce quality of life [158,159]. New treatments have been developed that aim to achieve both tumor control and functional preservation by partial ablation of the prostate while sparing the structures crucial for genitourinary function [158].
The use of laser ablation for prostate tumors is gaining traction as it allows for the precise delivery to ablate tumors via coagulative necrosis while sparing prostate parenchyma. Results from a phase I clinical trial in eight men with intermediate-risk prostate cancer showed successful ablation with MR-guided focal laser ablation [160]. No grade 3 or higher adverse events, changes in International Prostate Symptom Score, nor International Index of Erectile Function 5 occurred at 6 months [160]. Seven men had their prostate specific antigen (PSA) decrease, and follow-up magnetic-resonance-ultrasound fusion biopsy did not detect residual disease in the ablation zone in five men but did find cancer outside the treatment margin in

Prostate Tumors
The recent increase in screening measures has led to the detection of prostate cancers at earlier stages, calling into question the current standard treatments of radical prostatectomy, high dose prostate brachytherapy, and external beam radiation therapy that target the whole-gland prostate and reduce quality of life [158,159]. New treatments have been developed that aim to achieve both tumor control and functional preservation by partial ablation of the prostate while sparing the structures crucial for genitourinary function [158].
The use of laser ablation for prostate tumors is gaining traction as it allows for the precise delivery to ablate tumors via coagulative necrosis while sparing prostate parenchyma. Results from a phase I clinical trial in eight men with intermediate-risk prostate cancer showed successful ablation with MR-guided focal laser ablation [160]. No grade 3 or higher adverse events, changes in International Prostate Symptom Score, nor International Index of Erectile Function 5 occurred at 6 months [160]. Seven men had their prostate specific antigen (PSA) decrease, and follow-up magnetic-resonance-ultrasound fusion biopsy did not detect residual disease in the ablation zone in five men but did find cancer outside the treatment margin in six men [160]. These results indicate the potential need to increase treatment margins. Promising results were seen in 120 patients with low-to intermediate-risk prostate cancer who were treated with focal laser ablation, showing no changes in sexual and urinary functional scores, a decrease in PSA, and low morbidity [161]. A positive biopsy for clinically significant prostate cancer post-ablation was seen in 18 (15%) patients [161]. Figure 14 discusses the case of a patient with a prostate tumor treated with laser ablation.
While studies have shown the promise of ablation for prostate tumors, one of the present challenges in its adoption is adequate patient selection and precise disease localization [164,165]. The widespread adoption of multi-parametric MRI (mpMRI) has recently improved the detection of clinically significant prostate cancer, as evidenced by the PROMIS and PRE-CISION trials [166,167]. The mpMRI guidance has expanded the use of ablative modalities in prostate tumors, especially with transrectal ultrasound (TRUS)-MRI fusion for lesion targeting [165].
While generally safe, there are several risks of ablation of the prostate. Most complications typically occur within the first month of ablation and include hematuria, urinary tract infection, pain and discomfort, erectile dysfunction, dysuria, and urethral sloughing [168]. Recto-urethral fistula is a potential complication but a rare one and most often occurs when focal therapy is administered in a salvage setting and when the tumor is in the posterior portion of the prostate with extracapsular extension [168].  HIFU is the most well-studied ablative modality used for prostate tumors and has shown to be effective for posterior lesions [158,162]. A prospective clinical trial reported that hemiablation HIFU therapy had promising functional and oncological outcomes in patients with localized, unilateral prostate cancer [163]. IRE is another focal therapy modality that has been gaining recent attention in men with prostate cancer. A recent meta-analysis demonstrated that IRE preserves urinary and erectile function at relatively high rates while also being safe with good oncologic outcomes. Figure 15 discusses the case of a patient with a prostate tumor treated with IRE. Other ablation techniques for prostate tumors include cryoablation, vascular-targeted photodynamic therapy (VP), RFA, MWA, and brachytherapy, but further comparative studies are needed.
While studies have shown the promise of ablation for prostate tumors, one of the present challenges in its adoption is adequate patient selection and precise disease localization [164,165]. The widespread adoption of multi-parametric MRI (mpMRI) has recently improved the detection of clinically significant prostate cancer, as evidenced by the PROMIS and PRECISION trials [166,167]. The mpMRI guidance has expanded the use of ablative modalities in prostate tumors, especially with transrectal ultrasound (TRUS)-MRI fusion for lesion targeting [165].  While generally safe, there are several risks of ablation of the prostate. Most complications typically occur within the first month of ablation and include hematuria, urinary tract infection, pain and discomfort, erectile dysfunction, dysuria, and urethral sloughing [168]. Recto-urethral fistula is a potential complication but a rare one and most often occurs when focal therapy is administered in a salvage setting and when the tumor is in the posterior portion of the prostate with extracapsular extension [168].

Primary and Metastatic Lung Tumors
Lung cancer is the leading cause of cancer death for both men and women worldwide [169]. While radical resection is the treatment of choice for patients with lung cancer, only about 20-30% of patients are operable [170]. Image-guided thermal ablation is one of the many non-surgical treatments that patients with unresectable lung cancer can have. The most widely used ablative techniques for lung cancer are RFA, MWA, and cryoablation [171]. Table 5 summarizes most comparative studies that have been carried out presently, showing that RFA and MWA are comparable regarding outcomes and safety, while cryoablation still needs to be studied further. Figure 16 discusses the case of a patient with right lower lobe lung lesion treated with cryoablation. Very few studies address primary lung cancer alone and combine primary tumors with pulmonary metastases. While ablation is generally safe in patients with lung cancer with a mortality rate <1%, it has the potential to lead to multiple complications, including pneumothorax, pleural effusion, and parenchymal hemorrhage [177]. Potentially fatal complications typically include major hemorrhage, pneumothorax that becomes intractable due to bronchopleural fistula, pulmonary artery pseudoaneurysm, formation of systemic air embolism, and pneumonitis [177]. A single center's experience with 1000 RFAs in 420 patients found four deaths related to RFA, of which three patients died of interstitial pneumonia and one of hemothorax [178]. The major complication rate was 9.8%, and frequent complications include aseptic pleuritis (2.3%), pneumonia (1.8%), lung abscess (1.6%), bleeding that required blood transfusion (1.6%), pneumothorax that required pleural sclerosis (1.6%), bronchopleural fistula (0.4%), brachial nerve injury (0.3%), tumor seeding (0.1%), and diaphragm injury (0.1%) [178]. A single center's experience with 204 MWAs in 184 patients found a major complication rate of 20.6%, in which 15.7% of cases resulted in pneumothorax, 2.9% of cases resulted in pleural effusions requiring chest tube placements, and 2.9% of cases resulted in pneumonia [179]. With regard to cryoablation, the most common complications include pneumothorax, hemoptysis, pleural effusion, injury to the phrenic nerve, and implantation of the tumor [180].

Primary and Metastatic Bone Tumors
Bone is a common site of metastasis and lesions here are often painful and can lead to many complications like fractures, hypercalcemia, and spinal cord compression [181][182][183]. While surgical resection and bone curettage are the primary treatment for bone tumors, not all tumors can be accessed surgically and the can often impact the quality of life by affecting ambulation and causing pain [184]. Recent attention has been placed on minimally invasive techniques that can improve both quality of life and local tumor control in patients with bone tumors [184,185]. These techniques include percutaneous thermal ablation like RFA, MWA, and cryoablation that are becoming well-established as safe and effective treatment options for primary and metastatic tumors [182,186].
A 2019 meta-analysis involving RFA, MWA, cryoablation, and magnetic-resonance- An image was obtained and placed into the medical record. Samples were obtained for evaluation. Cryoablation was performed with three freeze cycles that lasted three, seven, and ten minutes, respectively, interposed with three minutes passive thaw cycles. (E) 6 and (F) 12-month follow up images show shrinking scar.

Primary and Metastatic Bone Tumors
Bone is a common site of metastasis and lesions here are often painful and can lead to many complications like fractures, hypercalcemia, and spinal cord compression [181][182][183]. While surgical resection and bone curettage are the primary treatment for bone tumors, not all tumors can be accessed surgically and the can often impact the quality of life by affecting ambulation and causing pain [184]. Recent attention has been placed on minimally invasive techniques that can improve both quality of life and local tumor control in patients with bone tumors [184,185]. These techniques include percutaneous thermal ablation like RFA, MWA, and cryoablation that are becoming well-established as safe and effective treatment options for primary and metastatic tumors [182,186].
A 2019 meta-analysis involving RFA, MWA, cryoablation, and magnetic-resonanceguided focused ultrasound (MRgFUS) found that all techniques resulted in pain relief after 1 and 3 months, in up to 91% and 95% of patients, respectively, though MRgFUS was found to have a noteworthy complication rate while the others were relatively safe [186]. While more comparative studies are needed, several systematic reviews, clinical trials, and cohort studies have shown the safety and effectiveness of RFA, MWA, and cryoablation for primary and metastatic bone tumors [184,[187][188][189][190][191][192][193][194][195].
Each of the primary ablation modalities has specific clinical indications and established clinical applications. With regards to RFA, it can be used to treat benign tumors and has been advocated as a first-line treatment for spinal osteoid osteomas (OOs) and osteoblastomas (OBs) as it is associated with improved pain scores and quality of life [196]. RFA is also effective for managing painful primary and metastatic bone tumors, especially those ≤2 cm in size, as well as lytic tumors with neoangiogenesis and mechanical instability [196]. Figure 17 discusses the case of a patient with a well-corticated osteoid osteoma in the posteromedial tibial metaphysis treated with RFA.

Primary and Metastatic Soft Tissue Tumors
Like bone tumors, soft tissue tumors can lead to chronic, severe pain and many complications, such as ulceration and mass effect [200]. While many soft tissue tumors are radiosensitive, a lot of them are not suited for radiation or surgery due to their location and adjacent structure, in which case, ablation remains an option. Percutaneous ablation can also prevent ulceration in certain soft tissue tumors of the skin or superficial locations [200].
The CRYODESMO-01 prospective, open-label non-randomized, non-comparative, multicenter trial found that cryoablation significantly improved functional status, reduced pain, and led to long-term disease control in non-abdominopelvic progressing desmoid tumors [201]. Cryoablation, as well as laser ablation, has also been shown to be ef- Cryoablation is useful for bone tumors in that it can produce very large ablation zones with less pain in contrast to other modalities. It is also favored in sclerotic metastases compared to RFA due to the insulating effects of cortical bone. However, cryoablation is limited in that the ice ball size cannot be visualized in dense bone, and it can be associated with technical difficulty for tumors close to vital structures like the spinal cord or nerves. It is favored in sclerotic metastases when compared to RFA due to the insulating effects of cortical bone. Furthermore, cryoablation has fewer neural complications as it does not require electrical changes [196].
MWA has faster coagulation times, deeper penetration, and experiences reduced osseous impedance when compared to other ablative modalities, making it useful for deep and large lesions with less heat sink and charring buildup effects [196]. However, manufacturer guidelines are mainly calibrated for soft tissue tumors; hence, parameters for bone tumors need further optimization [197].
Interstitial laser ablation is also used in bone tumors and offers great precision with minimal effects to adjacent tissues and reduces costs for chemoprotection with extraspinal bone procedures [196]. This modality also preserves the overlying skin, providing a favorable cosmetic outcome.
MRg-HIFU is a noninvasive modality that has been used for OO and OB as well as bone metastasis, multiple myeloma, plasmacytoma, and other diseases [196]. It is particularly useful for flat bones with thin cortices (e.g., the iliac bone and scapula) with a low-volume disease load due to the insulating properties of cortical bone [196]. They are best suited for lesions between 1 cm and 12 cm as they cannot be too close for risk of skin burns and cannot be too deep given the poor penetrability of US [196].
Ablation for bone tumors is generally safe. In a retrospective study of 169 patients undergoing RFA for 217 tumors, the major complication rate was 2.3% (five patients) with four patients having secondary fractures [198]. The minor complication rate was 27.7% (60 patients) with the most frequent complication being immediate postoperative pain [198]. Other risks to ablating bone tumors include cortical loss and cement leakage [199]. This leakage is particularly more vulnerable when osteoplasty is done with cryoablation as the cooler temperature delays cement polymerization [199]. In contrast, thermal ablation modalities can accelerate cement polymerization and prevent further injection to strengthen the bone [199]. Other complications include inadvertent nerve and osteochondral injury near bone [199].

Primary and Metastatic Soft Tissue Tumors
Like bone tumors, soft tissue tumors can lead to chronic, severe pain and many complications, such as ulceration and mass effect [200]. While many soft tissue tumors are radiosensitive, a lot of them are not suited for radiation or surgery due to their location and adjacent structure, in which case, ablation remains an option. Percutaneous ablation can also prevent ulceration in certain soft tissue tumors of the skin or superficial locations [200].
The CRYODESMO-01 prospective, open-label non-randomized, non-comparative, multicenter trial found that cryoablation significantly improved functional status, reduced pain, and led to long-term disease control in non-abdominopelvic progressing desmoid tumors [201]. Cryoablation, as well as laser ablation, has also been shown to be effective as second-line treatments for certain symptomatic vascular anomalies [202]. Figure 18 demonstrates a case of a patient with right breast sarcoma treated with CT-guided cryoablation.
RFA has been shown to be effective for desmoid tumors, myeloma, soft tissue metastasis, and plasmacytomas [196,203]. Multiple studies have found RFA to be associated with high local tumor control rates with favorable overall survivals and minimal adverse events [204][205][206][207]. Currently, RFA is the most widely used technique for metastatic sarcoma [208].
Like in bone tumors, HIFU is also particularly useful in treating soft tissue tumors. It has been utilized for metastasis, multiple myeloma, plasmacytoma, and many other focal myeloproliferative disorders [196]. A multicenter retrospective analysis found that MRgFUS significantly reduced tumor volumes and pain in fifteen patients with extraabdominal desmoid fribomatosis [209].
Complications of soft tissue tumors are similar to those of bone tumors, and most are due to the tumor's location. If superficially located, these soft tissue tumors can lead to skin injury when ablated. Furthermore, there can be iatrogenic thermal damage to surrounding structures like nervous tissue, adjacent bowel, or other viscera [200]. Complications of soft tissue tumors are similar to those of bone tumors, and most are due to the tumor's location. If superficially located, these soft tissue tumors can lead to skin injury when ablated. Furthermore, there can be iatrogenic thermal damage to surrounding structures like nervous tissue, adjacent bowel, or other viscera [200].

Conclusions
Image-guided percutaneous ablation is becoming a well-established alternative to surgery in many different cancers as there is growing evidence of its effectiveness and safety profile in ablating both primary and metastatic tumors in various organs. Ablation allows for shorter recovery, less bleeding, and fewer risks than conventional treatment, and is transforming the treatment options available for patients. As this minimally invasive practice is becoming more widely adopted with frequent advancements in both technique and available ablation modalities, more efforts are needed to establish and update existing protocols to include ablation in the treatment of oncologic patients.   (C) Axial non-enhanced CT image during cryoablation shows two cryoprobes (white arrows) traversing the target lesion (white arrowheads). The lesion is less visible having become nearly iso-dense to fat due to freezing. (D) Axial non-enhanced CT image at the conclusion of cryoablation shows the two cryoprobe-ghost trajectories (white arrows) after the probes were removed (white arrowheads). (E) Axial gadolinium-enhanced T1-weighted, fat-suppressed MR image 2-years after cryoablation, shows a shrinking, non-enhancing, necrotic lesion surrounded by a thin rim of fibrous tissue (arrowheads).

Conclusions
Image-guided percutaneous ablation is becoming a well-established alternative to surgery in many different cancers as there is growing evidence of its effectiveness and safety profile in ablating both primary and metastatic tumors in various organs. Ablation allows for shorter recovery, less bleeding, and fewer risks than conventional treatment, and is transforming the treatment options available for patients. As this minimally invasive practice is becoming more widely adopted with frequent advancements in both technique and available ablation modalities, more efforts are needed to establish and update existing protocols to include ablation in the treatment of oncologic patients.