Search Results (140)

Very-high-energy electrons, coupled with ultra-high dose rates, are being explored for their potential use in radiotherapy to treat deep-seated tumours. The dose per pulse needed to achieve ultra-high dose rates far exceeds the limit of current medical linear accelerator capabilities. A high dose per pulse has been observed as the limiting factor for many existing dosimeters, resulting in saturation at doses far below what is required. The MOSkin, an existing clinical quality assurance dosimeter, has previously been demonstrated as dose rate independent but has not been subjected to a high dose per pulse. Within this study, the MOSkins dose-per-pulse response was tested for linearity, with a dose per pulse as high as 23 Gy within 200 ns at the ANSTO Australian Synchrotron’s Pulsed Energetic Electrons for Research facility. While using EBT-XD film as a reference dosimeter, a dose rate dependence of the EBT-XD was discovered. Once confirmed and a correction factor established, EBT-XD was used as an independent reference measurement. This work presents confirmation of the MOSkin suitability for ultra-high dose-rate environments with an electron energy of 100 MeV, and a theoretical discussion of its dose-rate and dose-per-pulse independence; the MOSkin is the only detector suitable for both clinical quality assurance, and ultra-high dose-rate measurements in its standard, unmodified form. Full article

Background: We present the implementation of an in vivo dosimetry program that enhances treatment setups, ensuring high accuracy that is needed globally. This approach proves valuable in smaller departments by helping to detect and prevent errors. Evaluation studies have shown that in vivo dosimetry is a reliable method for assessing the overall accuracy of treatment delivery. Methods: Comprehensive development and validation of an in vivo dosimetry program using silicon diodes, ionization chambers, and calibrated electrometers for accurate radiation in dose measurements for treatments involving Co-60 or 6 MV X-ray beams. Results: The outcomes demonstrated that all diodes were dependable, with deviations of less than 1% (0.89 ± 0.10 cGy). Calibration curves were generated, showing dose variations of only 0.13% in the diode readings. The overall analysis revealed a mean deviation of up to 1%. Conclusions: These results provide a thorough assessment for patients’ treatment and facilitate timely interventions when needed, helping to ensure that dose variations stay within acceptable limits. Full article

This work introduces an original approach to the manufacturing of ionizing radiation-sensitive systems for radiotherapy applications—dosimetry. They are based on the Fricke dosimetric solution and the formation of macro-gels and capsules, and nano- and micro-gels. The reaction of ionic polymers, such as sodium alginate, with Fe and Ca metal ions is employed. Critical polymer concentration (c*) is taken as the criterion. Reaction of ionic polymers with metal ions leads to products related to c*. Well below c*, nano- and micro-gels may form. Above c*, macro-gels and capsules can be prepared. Nano- and micro-gels containing Fe in the composition can be used for infusion of a physical gel matrix to prepare 2D or 3D dosimeters. In turn, macro-gels can be formed with Fe ions crosslinking polymer chains to obtain radiation-sensitive hydrogels, so-called from wall-to-wall, serving as 3D dosimeters. The encapsulation process can lead to capsules with Fe ions serving as 1D dosimeters. This work presents the concept of manufacturing various gel structures, their main features and manufacturing challenges. It proposes new directions of research towards novel dosimeters. Full article

The results of radiotherapy in patients with primary malignant brain tumors are extremely dissatisfactory: the overall survival after a diagnosis of glioblastoma is typically less than three years. The development of spatially fractionated radiotherapy techniques could help to improve this bleak prognosis. In order to develop technical equipment and organ-specific therapy plans, dosimetry studies as well as radiobiology studies are conducted. Although perfect spheres are considered optimal phantoms by physicists, this does not reflect the wide variety of head sizes and shapes in our patient community. Depth from surface and X-ray dose absorption by tissue between dose entry point and target, two key parameters in medical physics planning, are largely determined by the shape and thickness of the skull bone. We have, therefore, designed and produced a biomimetic tool to correlate measured technical dose and biological response in human cancer cells: a brain phantom, produced from tissue-equivalent materials. In a first pilot study, utilizing our phantom to correlate technical dose measurements and metabolic response to radiation in human cancer cell lines, we demonstrate why an anthropomorphic phantom is preferable over a simple spheroid phantom. Full article

This work presents a Fricke radiochromic gel dosimeter with xylenol orange (XO) and a gelatin matrix modified with sorbitol. The dosimeter, combined with 2D scanning using a flatbed scanner and data processing using dedicated software packages, creates a radiotherapy dosimetry measurement system. The dosimeter reacts to ionizing radiation by changing color as a result of the formation of complexes of Fe³⁺ and XO molecules. It was characterized in terms of thermal and chemical stability and mechanical properties. The presence of sorbitol improved the mechanical and thermal properties of the dosimeter. The dosimeter maintains chemical stability, enabling its use in dosimetric applications, for at least six weeks. The dose–response characteristics of the dosimeter are discussed and indicate a dynamic dose–response of the dosimeter (up to saturation) of about 20 Gy and a linear dose–response of about 12.5 Gy. The following applications of the dosimeter are discussed: (i) as a 2D dosimeter in a plastic container for performing a coincidence test of radiation and mechanical isocenters of a medical accelerator, and (ii) for in vivo dosimetry as a 2D dosimeter alone and simultaneously as a bolus and a 2D dosimeter. Research has shown that the dosimeter has promise in many applications. Full article

Objective: The objective of this study was to develop and assess the clinical feasibility of auto-segmentation and auto-planning methodologies for automated radiotherapy in prostate cancer. Methods: A total of 166 patients were used to train a 3D Unet model for segmentation of the gross tumor volume (GTV), clinical tumor volume (CTV), nodal CTV (CTVnd), and organs at risk (OARs). Performance was assessed by the Dice similarity coefficient (DSC), the Recall, Precision, Volume Ratio (VR), the 95% Hausdorff distance (HD95%), and the volumetric revision degree (VRD). An auto-planning network based on a 3D Unet was trained on 77 treatment plans derived from the 166 patients. Dosimetric differences and clinical acceptability of the auto-plans were studied. The effect of OAR editing on dosimetry was also evaluated. Results: On an independent set of 50 cases, the auto-segmentation process took 1 min 20 s per case. The DSCs for GTV, CTV, and CTVnd were 0.87, 0.88, and 0.82, respectively, with VRDs ranging from 0.09 to 0.14. The segmentation of OARs demonstrated high accuracy (DSC ≥ 0.83, Recall/Precision ≈ 1.0). The auto-planning process required 1–3 optimization iterations for 50%, 40%, and 10% of cases, respectively, and exhibited significant better conformity (p ≤ 0.01) and OAR sparing (p ≤ 0.03) while maintaining comparable target coverage. Only 6.7% of auto-plans were deemed unacceptable compared to 20% of manual plans, with 75% of auto-plans considered superior. Notably, the editing of OARs had no significant impact on doses. Conclusions: The accuracy of auto-segmentation is comparable to that of manual segmentation, and the auto-planning offers equivalent or better OAR protection, meeting the requirements of online automated radiotherapy and facilitating its clinical application. Full article

This study presents a comprehensive dosimetric characterization and commissioning of a grid-type collimator manufactured via 3D printing using PLA-W composite filament, following an international protocol for small-field dosimetry. PLA doped with high concentrations of tungsten (>90% w/w) enables the fabrication of miniaturized collimators (<1 cm) with complex geometries, suitable for non-conventional radiotherapy applications. However, accurate assessment of spatial dose modulation is challenged by penumbra overlap between closely spaced beamlets, limiting the application of conventional instrumentation and protocols. To address this, absolute and relative dose distributions were evaluated for various radiation field configurations (number of beamlets) in both lateral and depth directions. Measurements were performed according to the IAEA TRS-483 protocol, using micro-ionization chambers and diode detectors. Additionally, long-term stability assessments were carried out to evaluate both the structural integrity and modulation performance of the printed grid over time. Point dose measurements using the same detectors were repeated after one year, and 2D surface dose distributions measured with EBT3 films were compared to SRS MapCHECK measurements two years later. The generated radiation field size of the central beamlet (FWHM) differed by less than 0.2% (15.8 mm) from the physical projection size (15.6 mm) and the lateral transmission due simultaneous beamlets resulted in FWHM variations of less than 3.8%, confirming manufacturing precision and collimator capability. Output factor measurements increased with the number of beamlets, from 0.75 for a single beamlet to 0.82 for the full beamlets configuration. No significant changes were observed in the depth of maximum dose across the different beamlets configurations (1.20 ± 0.20 cm). On the other hand, the long-term evaluations show no relevant changes in the FWHM or VPR, confirming the performance and reliability of the system. These results support the clinical feasibility and lasting performance stability of in-house manufactured grid collimators using PLA-W filaments and accessible 3D printing technology. Full article

Purpose: Image-guided radiotherapy (IGRT) has been widely implemented in the treatment of prostate cancer, offering a number of advantages regarding the precision of dose delivery. This study provides an overview of factors, clinical and physical alike, that increase treatment accuracy in prostate cancer radiotherapy in the context of IGRT. The following aspects are explored based on recent literature: the radiotherapy technique used in conjunction with IGRT, the type and frequency of IGRT, the impact of radiotherapy technique/IGRT on target dosimetry and organs at risk, the influence of IGRT on planning target volume margins, the impact of treatment time on dosimetric outcome and clinical outcomes using IGRT repositioning or an online adaptive plan. Methods: A systematic search of the literature was conducted within Pubmed/Medline databases to find relevant studies. Of the 152 articles fulfilling the initial search criteria, 79 were selected for final analysis. Results: The frequency of image guidance, the treatment regimen and the radiation technique are important factors that contribute to the optimization and personalization of the treatment plan. The daily anatomy and volume of the bladder and rectum can vary considerably, which can significantly impact the dosimetric effects on these organs. When used in conjunction with volumetric modulated arc therapy, IGRT allows for shaping the dose distribution to avoid nearby critical structures such as the bladder and rectum. Conclusions: Precise tumor targeting via IGRT can result in fewer geometric uncertainties, thereby improving treatment outcome both in terms of superior target coverage and sparing organs at risk. Full article

Background: Cervical cancer treatment with advanced radiotherapy techniques benefits from image guidance, particularly when anatomical changes occur during therapy. This case emphasizes the need for adaptive radiotherapy when target volume shifts significantly. Methods: A 70-year-old woman with International Federation of Gynecology and Obstetrics (FIGO) IIIC2 9th edition cervical squamous cell carcinoma presented with a distended uterine cavity due to fluid accumulation. She underwent definitive chemoradiotherapy using Volumetric Modulated Arc Therapy (VMAT) and weekly cisplatin. Results: Daily Cone Beam Computed Tomography (CBCT) imaging revealed progressive uterine shrinkage as intrauterine fluid drained, significantly altering target volume and organ-at-risk (OAR) positioning. These changes necessitated two re-planning CT scans during external beam radiotherapy to maintain accurate dosing and avoid OAR toxicity. The patient completed treatment, including image-guided brachytherapy, without complications. Adaptive planning ensured adequate tumor coverage and minimized normal tissue exposure. Conclusions: This case highlights the critical role of daily CBCT in detecting anatomical changes during radiotherapy. Adaptive re-planning, though rarely required more than once, was essential here to preserve treatment accuracy. CBCT should be considered a standard verification tool in cervical cancer radiotherapy, particularly in cases involving intrauterine fluid. Full article

Background: Prone breast radiotherapy has been shown to optimally spare the dose to the heart and lungs; we report on the heart and left anterior descending coronary artery (LAD) dosimetry and their implications for current care. Aims: (I) To measure the mean heart dose (MHD) and LAD mean and maximum doses (Dmean and Dmax) in patients with left-side breast cancer who have undergone hypo-fractionated whole breast radiotherapy (WBRT) with a concomitant boost to the post-operative cavity (40.50 Gy to the breast and 48 Gy to the cavity in 15 fractions) in the prone position; (II) to compare the dosimetry results to those reported in the literature for other techniques. Materials and Methods: In a consecutive series of 524 irradiated left-side breast cancer patients, heart and LAD dosimetry data were collected and correlated to breast volume and the volume of the radiation boost to the tumor cavity. A descriptive statistical analysis was performed to compare the same dosimetry data with those reported in the literature from supine techniques. To account for dosimetry differences in hypo-fractionation and conventional fractionated regimens (50–60 Gy in 25–30 fractions) reported in the literature, the cardiac doses were converted to the equivalent dose in 2 Gy fractions (EQD2). As previously reported, the prone setup protocol placed the medial edges of the tangential radiation fields at least 2.5 mm from the contoured LAD. Results: In all patients’ plans, the target coverage was successfully achieved. The mean values (±SD) were as follows: MHD = 0.69 Gy (±0.19) (EQD2 0.35 Gy ± 0.1); LAD Dmean = 2.20 Gy (±0.68) (EQD2 1.18 Gy ± 0.35); LAD Dmax = 4.44 Gy (±1.82) (EQD2 2.55 Gy ± 0.97). The values were consistently lower compared with those achieved by the multiple supine techniques reported in the literature. Spearman’s correlation analysis revealed a strong positive correlation between LAD and heart dosimetry variables. In contrast, no strong correlation was observed between the cardiac dose metrics and breast volume, boost volume, or their ratio index. A linear correlation was detected between LAD Dmean and LAD D2% (R² 0.64); LAD D2% and heart D2% (R² 0.60); LAD Dmax and heart D2% (R² 0.41). Conclusions: The prone position protocol minimizes heart and LAD exposure. This approach results in a dosimetry advantage when compared with more complex and expensive WBRT techniques in the supine position. Full article

FLASH radiation therapy is an emerging technique that provides several advantages over conventional radiotherapy. By delivering ultra-high dose rate radiation, the damage to healthy tissues surrounding the treatment area is minimized, treatment time is reduced and treatment outcomes of radioresistant tumors are improved. Despite its promising potential, FLASH radiation therapy remains relatively understudied, particularly in the field of dosimetry. Polymer gel dosimetry is a promising technique for verifying FLASH radiation therapy because it enables volumetric dose distribution measurements with high spatial accuracy. This study investigates the applicability of two commonly used polymer gel dosimeters, nPAG and NIBMAGAT, enhanced with nanoparticles, in ultra-high dose rate radiation therapy. The results indicate that NIBMAGAT gel, enriched with Ag nanoparticles, outperforms nPAG. NIBMAGAT gel exhibits less saturation at high doses, maintains dose rate independence and offers comparable sensitivity to nPAG formulation. Full article

Postmastectomy radiation therapy (PMRT) is an adjuvant treatment for breast cancer. Some mastectomized women undergoing PMRT can have breast reconstruction with expander implant reconstruction. However, the expander implant contains a magnetic metal port for its inflation, and in patients with a high risk of recurrence, the PMRT is performed before the expander replacement. The difficulties in radiation treatment near high-Z metals are mainly due to dose alterations around them. Therefore, this study proposes using a realistic breast phantom and gel dosimetry to investigate the effects of the metallic parts of the expandable prosthesis on the 3D delivery of the treatment. A conformal radiation treatment was planned and delivered to the gel phantom with the metal port. MAGIC-f gel was used with magnetic resonance imaging for dose assessment. The treatment plan dose distribution was compared to the measured dose distribution by gamma analysis (3%/3 mm/15% threshold). A significant gamma fail region was found near the metal port, corresponding to a dose reduction of approximately 5%. This underdose is within the tolerance threshold for dose heterogeneity established by the International Commission on Radiation Units (ICRU), but should be considered when treating these patients. Full article

A novel reusable silicon foil dosimeter based on the new emerging optically stimulated luminescence (OSL) material MgB₄O₇:Ce,Li (MBO) is developed and characterized for dosimetric verification of spatially resolved radiotherapy doses. Direct comparison of the spatial (two-2D towards three-3D) proton dose mapping can be achieved with an appropriately designed optical detection setup equipped with a light source (e.g., LEDs) that illuminates the dosimeter and a highly sensitive CCD camera that simultaneously acquires the 2D OSL light from the foil. The newly designed (2nd generation) optical setup allows the registration of high-resolution 2D proton doses (below 0.1 mm resolution) and reconstruction of the 2D proton dose distribution with an accuracy comparable to that of the Gafchromic^TM foils, the current standard of passive 2D dosimetry in radiotherapy. This article outlines the technology’s potential application with respect to the commercially available Gafchromic^TM EBT3 films in measurements of the clinically relevant, spatial proton dose mapping. The obtained comparison of the proton radial dose profiles (for EBT3 films vs MBO foils) agrees within 5%. The resulting image resolution (0.074 mm/px for MBO foil) corresponded well with the tested EBT3 films (0.085 mm/px), indicating excellent properties for future 3D proton dose verifications of modern radiotherapy techniques (e.g., proton radiotherapy). Full article

Background: Radiotherapy technology has undergone significant advancements, driven by the pursuit of improved tumor control probabilities and reduced normal tissue complication probabilities. This has been achieved primarily through innovative approaches that prioritize high dose conformity on complex treatment targets. The CONVERAY project introduces a groundbreaking teletherapy system featuring a convergent X-ray beam, which enables highly conformal dose distributions by converging photons to a focal spot, thereby achieving exceptionally high fluence rates. Methods: Customized Monte Carlo subroutines have been developed to simulate particle fluence and associated dosimetry effects for the CONVERAY device. This simulation approach facilitated a detailed, step-by-step characterization of radiation fluence and interaction processes, enabling seamless integration with a conventional clinical linear accelerator head. Key physical properties of the radiation beam have been comprehensively characterized for various CONVERAY configurations, providing a solid foundation for evaluating the corresponding dosimetry performance. Results: Monte Carlo simulations successfully tracked the phase state of the CONVERAY device, characterizing the influence of individual components on convergent photon beam production. Simulations evaluated dosimetry performance, confirming the device’s capability to achieve high dose concentrations around the focal spot. Preliminary tests on realistic scenarios (intracranial and pulmonary irradiations) demonstrated promising spatial dose concentration within tumor volumes, while gantry rotation significantly improved dose conformation. Conclusions: This proof-of-concept Monte Carlo study of the CONVERAY prototype provided critical insights into the generation of convergent X-ray beams, validating the device’s ability to achieve its primary objective. Notably, simulation results reveal the potential for exceptionally high dose concentrations within complex treatment volumes, demonstrating promising dosimetry performance. Full article

In vivo dosimetry (IVD) is a vital component of modern radiotherapy, ensuring accurate and safe delivery of radiation doses to patients by measuring dose parameters during treatment. This paper provides a comprehensive overview of IVD, covering its fundamental principles, historical development, and the technologies used in clinical practice. Key techniques, including thermoluminescent dosimeters (TLDs), optically stimulated luminescent dosimeters (OSLDs), diodes, metal-oxide-semiconductor field-effect transistors (MOSFETs), and electronic portal imaging devices (EPIDs), are discussed, highlighting their clinical applications, advantages, and limitations. The role of IVD in external beam radiotherapy, brachytherapy, and pediatric treatments is emphasized, particularly its contributions to quality assurance, treatment validation, and error mitigation. Challenges such as measurement uncertainties, technical constraints, and integration into clinical workflows are explored, along with potential solutions and emerging innovations. The paper also addresses future perspectives, including advancements in artificial intelligence, adaptive radiotherapy, and personalized dosimetry systems. This entry underscores the critical role of IVD in enhancing the precision and reliability of radiotherapy, advocating for ongoing research and technological development. Full article