Impact of Patient Size and Positioning on Radiation Dose in Multiphase Liver CT Examinations

Abstract

Investigating the correlation between patient dimensions (Body Mass Index (BMI), weight, height) and radiation dose, the study also assesses the impact of the isocenter on dosage and X-ray tube. This retrospective study analyzed 258 consecutive three-phase liver CT exams (135 women, 123 men) performed on a Siemens SOMATOM Definition Edge scanner between January 3 and December 15, 2023. BMI, weight, height, maximum abdominal width (from topograms), and vertical isocenter status were extracted using the Dose&Care system and Horos software. BMI strongly correlated with total DLP in abdomen-plus-pelvis scans (r = 0.70) and moderately in abdomen-only scans (r = 0.54). Liver-phase DLP correlations were weaker (r = 0.44 and r = 0.28, respectively). Abdominal width showed similar associations with total DLP (r = 0.67 and r = 0.64) and liver-phase DLP (r = 0.41 and 0.37). Vertical mis-centering did not significantly affect total DLP (p = 0.174 and p = 0.705) or tube load. Patient size—not minor deviations from the isocenter—is the principal driver of radiation dose in multiphase liver CT. Automated, size-adapted protocols and restriction of scan range to clinically essential regions can preserve image quality while minimizing unnecessary radiation in routine practice.

1. Introduction

Computed tomography (CT) examination of the liver is used, among other diagnostic methods, to evaluate primary tumors or cancer metastases within this organ. It also helps identify, localize, and characterize cancerous lesions. CT also allows for the detection of liver pathologies such as cirrhosis, cysts, steatosis, or inflammatory lesions. After cancer treatment, during oncologic therapy, or over the course of other liver diseases, this examination makes it possible to monitor the progress of therapy and evaluate possible changes in the organ [1]. According to the data collected by the National Health Fund in Poland, 877 patients underwent liver imaging by CT scan in 2022 [2]. Statistics collected from various countries around the world as of 2021 state that the number of all CT scans performed averages 156.6 per 1000 people. The same study reports that in Poland there are 116.5 examinations per 1000 residents [3]. Given the frequency of CT scans, it is important to consider the factors affecting the safety of this examination, with particular attention to the possible effects of ionizing radiation on the human body. The dose of ionizing radiation used in performing imaging examinations can range from a few to tens of millisieverts (mSv). Many factors influence this parameter, including the examination protocol and equipment used. The patient’s body structure is also important, as different tissues absorb radiation differently [4]. The examinee is subjected to a different dose of radiation depending on the area of the body that requires imaging by radiation. The dose reduction techniques used, such as modern imaging technologies, optimization programs, as well as precise device settings, can significantly affect the radiation dose during the examination. The duration of the examination and the number of runs are also important [5]. Radiation dose management is a key aspect of medical diagnostics. Physicians, radiologists, and electroradiologists strive to adjust the parameters of the examination in such a way as to obtain the necessary diagnostic information with minimal exposure of the patient to ionizing radiation. The constant development of diagnostic technologies and procedures is aimed at continuous improvement and minimization of radiation dose, while keeping high diagnostic quality [6]. Although the radiation dose per individual examination has decreased over time due to advancements in imaging technology, optimized protocols, and increased awareness of radiation safety, the overall collective dose to the population continues to rise. This increase is largely driven by the growing number of imaging procedures being performed overall [7,8,9]. Currently, thanks to years of research, the harmful effects of even low doses of ionizing radiation on health have been demonstrated, which raise concerns about its potential health risks [10,11]. Ionizing radiation significantly increases cancer risk by inducing mutations in somatic cells. It can also impair the immune system, resulting in greater susceptibility to infections and other diseases. Therefore, it is important to minimize radiation exposure and adhere to reference dose levels tailored to specific examinations [12,13]. Researchers also emphasize the importance of personalized dose control, especially for vulnerable populations such as pediatric patients or individuals requiring frequent imaging follow-up [14,15]. In routine clinical practice, subtle misalignments in patient positioning—particularly shifts of the isocenter by just a few centimeters—often go unnoticed. When combined with an excessively large field of view (FOV), such positioning errors may result in unnecessary radiation exposure, even in patients with average body habitus. These factors, which are not accounted for by standard indices such as BMI, may significantly influence radiation dose metrics, including CTDIvol and DLP. This study investigates how subtle deviations in patient positioning and FOV selection affect CTDIvol and DLP values in clinical liver CT imaging, with the goal of identifying practical implications for radiation dose optimization.

2. Materials and Methods

A retrospective analysis was conducted on studies performed between 1 March and 15 December 2023 at a university hospital in Poland. Data were collected from Guerbet’s Dose&Care dose monitoring system.

Based on the data received from the dose monitoring system, the following were determined:

• Whether the patient was in the isocenter—Figure 1 shows the patient outside the isocenter, while Figure 2 shows the patient inside the isocenter.

2.

Information about the scope of the examination performed (abdominal or abdominal with pelvis)

3.

Number of phases performed for each test

4.

Total DLP (DLP for the entire study) and DLP for the liver imaging phase

Only studies for which 4 imaging phases were performed were used for analysis: native phase (phase before contrast administration), arterial phase, venous phase, and delay to the liver (standard at 3 min after contrast administration). Cases for which the patient’s weight or height was not given were also excluded.

In addition, the widest point in the abdominal area was measured on the patient’s toposcan in the Horos software (4.0.0 RC5). The measurement scheme is shown in Figure 3.

• Do BMI, weight, and patient height affect total DLP and DLP in the liver phase?
• Does the patient’s max dimension affect the total DLP and DLP in the liver phase?
• Does the patient’s max dimension correlate with BMI and weight?
• Does the max. patient size affect the X-ray tube performance (kV, mA)?
• Do the patient’s BMI, weight, and height affect the X-ray tube’s performance?
• Does the isocenter affect the total DLP and DLP in the liver phase?
• Does the isocenter affect the X-ray tube performance?

For the analysis, studies performed using a three-phase liver protocol in 258 patients (including 135 women and 123 men) were used. Due to missing data in some cases, the number of patients included may vary across individual statistical analyses. All examinations were performed using a Siemens SOMATOM Definition Edge scanner. The study group consisted of 80 abdominal and 178 abdominal and pelvic examinations. In our study, the isocenter shift did not exceed 5 cm. Patients were classified as being “in the isocenter” if the patient’s isocenter coincided with the scanner’s isocenter; otherwise, they were assigned to the “not in the isocenter” group.

Patient Characteristics

Patient demographics are summarized in

Table 1. Descriptive statistics for anthropometric variables in the two study cohorts.

Group	Variable	n	Mean ± SD	Median (IQR)
Abdomen	Height (m)	80	1.69 ± 0.09	1.70 (1.63–1.76)
Abdomen	Weight (kg)	80	80.4 ± 14.1	79 (69–90)
Abdomen	BMI (kg m−2)	80	28.0 ± 4.2	27.9 (25.1–30.8)
Abdomen + Pelvis	Height (m)	178	1.68 ± 0.09	1.68 (1.62–1.74)
Abdomen + Pelvis	Weight (kg	178	73.8 ± 13.9	72 (63–82)
Abdomen + Pelvis	BMI (kg m−2)	178	26.3 ± 4.3	25.5 (23.0–28.9)

. Patients in the Abdomen-only cohort (n = 80) had a mean height of 1.69 ± 0.09 m, a mean weight of 80.4 ± 14.1 kg, and a mean BMI of 28.0 ± 4.2 kg m⁻². The Abdomen + Pelvis cohort (n = 178) was similar in height (1.68 ± 0.09 m) but lighter (73.8 ± 13.9 kg) with a lower mean BMI of 26.3 ± 4.3 kg m⁻². Median and inter-quartile ranges (IQR) are provided for completeness. A detailed breakdown of BMI categories is available in

Table 2. Distribution of BMI categories in the two study cohorts.

Group	BMI Category	n (%)
Abdomen	Underweight (<18.5 kg m−2)	1 (1.3%)
Abdomen	Normal (18.5–24.9)	17 (21%)
Abdomen	Overweight (25.0–29.9)	40 (50%)
Abdomen	Obese (≥30)	22 (28%)
Abdomen + Pelvis	Underweight (<18.5 kg m−2)	2 (1.1%)
Abdomen + Pelvis	Normal (18.5–24.9)	52 (29%)
Abdomen + Pelvis	Overweight (25.0–29.9)	80 (45%)
Abdomen + Pelvis	Obese (≥30)	44 (25%)

.

3. Results

3.1. Is There a Statistically Significant Association Between BMI Values and DLP, as Well as DLP in the Liver Phase?

In our comprehensive study on the impact of BMI on radiation exposure during CT imaging, we performed a detailed analysis segmented by the anatomical focus of the scans: solely the abdomen (‘Abdomen’) and both the abdomen and pelvis (‘Abdomen + Pelvis’). Our objective was to discern whether BMI influences the DLP, both overall and specifically during the liver phase of imaging, within these distinct groups.

3.1.1. Group with Abdominal Imaging Only

The analysis of the ‘Abdomen’ group, encompassing 53 patient observations, reveals the following insights. We found a moderate positive correlation between BMI and total DLP (Spearman r = 0.54, p-value < 0.00001), as well as a significant, albeit weaker, correlation with DLP during the liver phase (Spearman r = 0.28, p-value = 0.030). These findings suggest that higher BMI is associated with increased radiation dose, but the effect is more pronounced in the total DLP compared to the liver phase (Figure 4).

3.1.2. Group with Abdomen and Pelvis Imaging

In the ‘Abdomen + Pelvis’ group, which included 146 patient observations, the analysis had a stronger association. The correlation between BMI and total DLP was notably robust (Spearman r = 0.70, p-value < 0.00001), alongside a moderate positive correlation with DLP during the liver phase (Spearman r = 0.44, p-value < 0.00001). This indicates a significant impact of BMI on radiation dose in more comprehensive imaging that includes both the abdomen and pelvis (Figure 5).

3.2. Is There a Statistically Significant Difference in DLP and DLP in the Liver Phase Values Depending on the Maximum Dimensions of the Patient?

3.2.1. Group with Abdominal Imaging Only

The analysis of the ‘Abdomen’ group, encompassing 80 patient observations, reveals the following insights. Analysis revealed a notable positive correlation (Pearson r = 0.67, p < 0.00001) between the maximum patient width and the overall DLP. This finding implies that an increase in patient size is typically associated with an elevation in the total DLP for abdominal scans (Figure 6). A moderate positive relationship (Pearson r = 0.41, p = 0.00016) was identified between patient width and DLP during the liver phase, suggesting a discernible but comparatively moderate association in this specific imaging phase (Figure 7).

3.2.2. Group with Abdomen and Pelvis Imaging

In the ‘Abdomen + Pelvis’ group, which included 175 patient observations, there was a strong positive correlation (Pearson r = 0.64, p < 0.00001) noted between the patient’s maximum width and the combined DLP for abdomen and pelvis imaging. This trend aligns with the findings from the abdominal-only group, where larger patient dimensions tend to correspond with increased total DLP values in combined abdomen and pelvis scans (Figure 8). The relationship between the maximum width and the DLP in the liver phase was moderately positive (Pearson r = 0.37, p < 0.00001). Although this correlation is positive, it is comparatively weaker than that observed for the total DLP values (Figure 9).

3.3. Is There a Statistically Significant Relationship Between the Maximum Dimensions of the Patient and the X-Ray Tube Output Parameters?

The analysis investigates the relationship between patients’ maximum dimensions (“Max width (cm)”) and various X-ray tube output parameters, separated into two groups: cases involving only the abdomen and cases involving both the abdomen and the pelvis.

3.3.1. Group with Abdominal Imaging Only

The ‘Abdomen’ group comprised 80 patient observations. Correlations were assessed for “kV”, “X-ray tube max power mA Phase I”, “X-ray tube max power mA Phase II”, and “X-ray tube max power mA Phase III” using Pearson’s correlation test (Figure 10).

• Tube current (mA), Phase I: Pearson r = 0.18, p-value = 0.11, suggesting a weak positive relationship with Max width (cm).
• Tube current (mA), Phase II: Pearson r = 0.18, p-value = 0.11, indicating a weak positive relationship with Max width (cm).
• Tube current (mA), Phase III: Pearson r = 0.19, p-value = 0.08, showing a weak positive relationship with Max width (cm).

The analysis of the “kV” data for the abdomen-only cases reveals that all the data points are identical, with a mean of 120.0 and standard deviation of 0.0. This uniformity in the “kV” values means that the correlation coefficient for “kV” is undefined in this subset of the data.

3.3.2. Group with Abdomen and Pelvis Imaging

The ‘Abdomen + Pelvis’ group includes 175 patient observations. Cases were analyzed with the same set of parameters as above. Correlations with kV were also calculated (Weight ↔ kV: Pearson r = 0.07, p = 0.36; BMI ↔ kV: Pearson r = 0.012, p = 0.88) but are not displayed in Figure 11 because none reached statistical significance.

• Tube current (mA), Phase I: Pearson r = 0.23, p-value = 0.002, suggesting a weak positive relationship with Max width (cm).
• Tube current (mA), Phase II: Pearson r = 0.16, p-value = 0.034, indicating a weak positive relationship with Max width (cm).
• Tube current (mA), Phase III: Pearson r = 0.19, p-value = 0.012, showing a weak positive relationship with Max width (cm).

3.4. Is There a Statistically Significant Difference in DLP Values Based on the Location of the Isocenter?

The analysis was conducted separately for two groups: cases involving only the abdomen and cases involving both the abdomen and pelvis. The Mann–Whitney U test was used to determine if there is a statistically significant difference in DLP values based on the isocenter location within each group.

3.4.1. Group with Abdominal Imaging Only

• Mann–Whitney U statistic: 256.0
• p-value: 0.174

The analysis of the ‘Abdomen’ group encompassed 80 patient observations. The p-value is 0.174, which is greater than the conventional alpha level of 0.05. Therefore, we do not have sufficient evidence to conclude that there is a statistically significant difference in DLP values based on the isocenter location for abdomen-only examinations (Figure 12).

3.4.2. Group with Abdomen and Pelvis Imaging

• Mann–Whitney U statistic: 1564.0
• p-value: 0.705

The analysis of the ‘Abdomen + Pelvis’ group encompassed 178 patient observations. The p-value is 0.705, which is greater than 0.05, indicating no significant difference in DLP values based on the isocenter location for examinations involving both the abdomen and pelvis (Figure 13).

3.5. Does the Patient’s BMI, Weight and Height Have a Statistically Significant Impact on X-Ray Tube Output’s Operating Parameters?

In the conducted analysis, we explored the relationship between patient physical characteristics (height, weight, and BMI) and the operating parameters of a medical X-ray tube (kV, mA in phases I, II, and III) across two distinct groups: patients undergoing procedures involving the abdomen and those involving both the abdomen and pelvis.

3.5.1. Group with Abdominal Imaging Only

The analysis of the ‘Abdomen’ group encompassed 53 patient observations. The average height, weight, and BMI of the patients were found to be 1.69 m, 80.35 kg, and 27.96, respectively. When exploring the correlation between these physical characteristics and the operating parameters of the medical X-ray tube, it was observed that the weight and BMI had a negligible impact on the kV settings, which remained constant at 120 kV for all patients. However, the mA settings in phases I, II, and III demonstrated slight variations, though not strongly correlated with height, weight, or BMI. This suggests that while patient physical characteristics are considered, they do not significantly alter the basic operating parameters of the X-ray tube in abdomen-focused procedures (Figure 14 and Figure 15).

3.5.2. Group with Abdomen and Pelvis Imaging

The analysis of the ‘Abdomen + Pelvis’ group encompassed 146 patient observations. Patients in this group presented an average height of 1.68 m, a weight of 73.80 kg, and a BMI of 26.26. Here, weight and BMI showed a more pronounced impact on the X-ray tube output’s mA settings across the three operational phases. Particularly, the correlation between BMI and the mA settings in the third phase was statistically significant (Figure 16 and Figure 17).

3.6. Does the Isocenter Have a Statistically Significant Impact on X-Ray Tube Output Parameters?

Key parameters, including kV and maximal power for the X-ray tube in three phases (mA I phase, mA II phase, and mA III phase), were analyzed. Statistical comparisons between cases with and without an isocenter were performed using independent t-tests because the two subgroups (with vs. without an isocenter) are mutually exclusive (i.e., the observations are independent), each outcome variable was approximately normally distributed with equal variances in the two groups (Shapiro–Wilk and Levene tests; both p > 0.05 or n ≥ 30), and the t-test therefore provides the most powerful unbiased test for comparing their means.

3.6.1. Group with Abdomen and Pelvis Imaging

The analysis of the ‘Abdomen’ group encompassed 80 patient observations. In this group, the presence of an isocenter did not demonstrate a statistically significant impact on the measured parameters. The p-values for E (mSv), kV, mA I phase, mA II phase, and mA III phase were 0.3225, N/A (due to uniformity across the sample), 0.5942, 0.5940, and 0.6262, respectively (

Table 3. Comparison of X-ray tube output parameters based on the presence or absence of an isocenter in a group limited to the abdomen.

Parameter	Mean with Isocenter	Mean Without Isocenter	p-Value (t-test)
kV	120	120	[Not applicable]
mA I Phase	800	794.87	0.5942
mA II Phase	800	794.83	0.5940
mA II Phase	765.90	744.37	0.6262

).

3.6.2. Group with Abdomen and Pelvis Imaging

The analysis of the ‘Abdomen + Pelvis’ group encompassed 178 patient observations. For this group, the analysis revealed no statistically significant impact of the isocenter on the X-ray tube’s operation parameters. The p-values for E (mSv), kV, mA I phase, mA II phase, and mA III phase were 0.6113, 0.4106, 0.6000, 0.6184, and 0.1403, respectively, indicating no significant differences between the groups with and without an isocenter (

Table 4. Comparison of X-ray tube output parameters based on the presence or absence of an isocenter in a group limited to abdomen and pelvis.

Parameter	Mean with Isocenter	Mean Without Isocenter	p-Value (t-test)
kV	119.05	119.62	0.4106
mA I Phase	799.33	797.81	0.6000
mA II Phase	799.33	794.48	0.6184
mA II Phase	708.52	642.40	0.1403

).

4. Discussion

Radiation dose management is crucial in medical diagnostics to balance obtaining the necessary diagnostic information with minimizing the patient’s exposure to radiation [16]. This study focused on analyzing the relationship between patient characteristics, radiation dose, and imaging parameters.

The results show a significant positive correlation between the patient’s maximum dimensions and BMI and total DLP for abdominal examinations. This correlation includes both the abdominal and pelvic abdominal examination groups. In addition, a moderately positive association was identified between patient width and DLP in the delayed phase for the liver. The above results underscore the impact of patient size on radiation dose, highlighting the need for tailored dose optimization strategies based on individual patient characteristics, which may include, for example, reducing the scope of the examination only to clinically relevant areas. It is noteworthy that a greater correlation was noted between patient BMI and total DLP than maximum patient width. Further analysis examined the relationship between patient dimensions and X-ray tube output parameters. However, in studies involving only the abdominal cavity, the relationship with X-ray tube power parameters (mA at different phases) was weak, suggesting that the effect of patient size on radiation dose has limited impact on specific X-ray tube performance parameters. In contrast, in studies involving the abdomen and pelvis, weight and BMI showed a greater effect on X-ray tube mA settings in the three phases of the study. In particular, the correlation between BMI and mA settings in the third phase (delay to the liver at 3 min after contrast administration) was statistically significant. The study also examined the effect of isocenter location on radiation dose and X-ray tube performance. Interestingly, the presence or absence of an isocenter showed no statistically significant effect on radiation dose or X-ray tube performance in either the abdominal-only or abdominal-pelvis groups. This suggests that isocenter location may not be a significant factor affecting these parameters in the study group. In contrast, for patients placed in the isocenter, the dose spread was significantly smaller, and the doses were more similar to each other.

Isa et al. conducted a study to evaluate the effect of patient positioning in the isocenter on radiation dose using two routine head scanning protocols: standard (120 kVp/180 mAs) and low dose (100 kVp/142 mAs). A standard cylindrical phantom made of polymethylmethacrylate (PMMA), placed at a height of 104 cm from the floor (reference isocenter), was used to measure dose. The positions of the phantom were then changed to simulate an alignment of 5 cm relative to the isocenter, in both the upward and downward directions, at heights of 109 cm, 114 cm, 119 cm, 124 cm, and 99 cm, 94 cm, 89 cm, 84 cm, respectively. The results of the effective dose measurements were as follows: the highest mean volume of the Computed Tomography Dose Index (CTDIvol) for Maximum Change in a Step (MCS) (upward change) was 105.06 mGy (at +10 cm), and for Minimum Change in a Step (MCI) (downward change) was 105.51 mGy (at −10 cm), which was significantly different (p < 0.05) compared to the isocenter. Significant differences (p < 0.05) were observed in the mean DLP value between the isocenter and MCS (85.8 mGy.cm) and MCI (93.1 mGy.cm). The introduction of the low-dose protocol resulted in significantly increased CTDIvol values for MCS (at +10 cm) and MCI (at −10 cm) compared to the isocenter [17].

In the study by S. Zensen et al. the authors focused on evaluating radiation dose in the context of CT-guided biopsies. Focused on abdominal examinations, our study analyzed a wide range of imaging studies, taking into account different procedures and body areas. In addition, our study aimed to identify general relationships between patient characteristics and radiation dose, as well as the effect of isocenter location and tube parameters on radiation exposure [18].

In the context of our analysis, an interesting comparison is the study by Abuzaid et al. that evaluated radiation doses in high-resolution computed tomography (HRCT) of the chest with patient size-specific dose estimates (SSDEs). Their retrospective analysis involving nearly 2000 patients showed a significant positive correlation between BMI and all key dose parameters, such as CTDIvol, DLP, and SSDEs. These findings are consistent with our observations of the relationship between BMI, body dimensions, and total DLP and delayed-phase DLP for the liver. Importantly, the authors emphasize that the use of SSDEs allows for more accurate dose matching to patient morphology than traditional metrics. Our study also shows the effect of patient size on exposure parameters; however, it focuses on the abdominal and pelvic region, while Abuzaid analyzed the thorax. Despite the anatomical differences, both studies point to the need to personalize imaging protocols according to patient characteristics [19].

An additional relevant comparison is the study by Woisetschläger et al., which evaluated the effect of patient positioning accuracy on radiation dose using a novel 3D camera-based system in CT imaging. The authors demonstrated that precise patient centering significantly reduces radiation dose, particularly in the chest, abdomen, and pelvis, by minimizing the degradation of automatic exposure control and bowtie filter performance. These findings partially contrast with our results, which did not show a statistically significant dose difference based on isocenter positioning [20].

The collected results indicate that patient body size, particularly BMI and maximum lateral dimension, has a significant impact on total radiation dose, emphasizing the need for personalized imaging protocols. These correlations were especially evident in scans encompassing both the abdomen and pelvis. For abdominal-only examinations, a weaker correlation between body size and exposure parameters (mA) was observed, possibly reflecting the effectiveness of automatic exposure control systems in compensating for anatomical differences. In our study, patient positioning at the isocenter did not show a statistically significant impact on radiation dose; however, this may be attributed to the binary classification method we applied and the broader scan range. In contrast, Isa et al., who focused on head CT, demonstrated clear dose differences when the phantom was positioned off-center, suggesting that isocenter accuracy may be more critical in small anatomical areas [17]. Similarly, Zensen et al.’s study on liver biopsies showed increased radiation exposure for deep lesions and additional helical scans, consistent with our findings on body size influence, though in a different clinical context (interventional vs. diagnostic procedures) [18]. The study by Abuzaid et al. found a strong correlation between BMI and all major dose metrics (CTDIvol, DLP, SSDEs) in chest CT, highlighting the advantages of SSDEs over traditional metrics for accurately adjusting dose to patient morphology. While their study focused on a different anatomical region, the observations align with ours. Interestingly, Abuzaid et al. also observed a negative correlation between scan length and CTDIvol/SSDEs, likely due to automatic exposure control systems, a relationship not observed in our data, possibly due to protocol differences [19]. Moreover, Woisetschläger et al. demonstrated that precise patient centering using a 3D camera system significantly reduced radiation dose in the chest, abdomen, and pelvis, partially contrasting with our findings. These discrepancies may result from methodological differences: Their study applied a continuous spatial evaluation, while ours used a binary classification. Their use of a standardized positioning aid may have captured subtle yet clinically relevant dose variations that traditional methods overlook [20]. Collectively, these studies underscore the importance of tailoring imaging parameters to patient characteristics and highlight the potential of positioning technologies to improve radiation safety and diagnostic quality.

Personalization of CT protocols based on patient body composition is needed. The observed increase in DLP values with rising BMI and body width confirms the validity of using differentiated exposure settings tailored to individual patient dimensions. In this context, broader implementation of automatic tube current modulation and the adoption of protocols based on indicators such as SSDE are recommended [19]. Although our study did not demonstrate a significant impact of isocenter positioning on radiation dose, these results may suggest that the precision of patient positioning plays a lesser role in examinations involving larger anatomical areas, such as the abdomen and pelvis. Conversely, other studies, such as that by Isa et al., have shown a significant influence of precise positioning in smaller scanning regions [17]. These discrepancies highlight the need for further research on the effect of isocentric positioning across different imaging protocols. Additionally, the findings may support the development of CT scanner software (Horos 4.0.0 RC5) towards automated exposure parameter adjustment and precise positioning using AI-assisted systems. Incorporating these conclusions into clinical practice could enhance patient safety by reducing unnecessary radiation exposure without compromising diagnostic image quality. At the same time, it would enable more efficient use of available technological resources and contribute to the standardization of high-quality radiological care.

It is important to note the limitations of the study, such as its retrospective nature and its focus on a specific medical facility. Additionally, the lack of statistically significant differences in some analyses may be due to sample size or other unaccounted variables. Future studies could focus on a broader patient population and consider additional factors that may influence variable radiation dose.

5. Conclusions

This study demonstrates that patient size—particularly BMI, body weight, and maximum transverse dimension—has a significant impact on radiation dose metrics (total DLP and liver phase DLP) and on tube current settings during multiphase liver CT examinations. Among these parameters, maximum body width, extracted from scout images, shows a strong correlation with radiation dose, highlighting the relevance of direct geometric measurements alongside commonly used anthropometric indices.

Our results further indicate that patient size influences X-ray tube output parameters, especially tube current (mA), with more pronounced effects observed in extended scan protocols (abdomen + pelvis). While tube voltage (kV) remained largely unaffected, the data suggest that exposure control systems adjust mA in response to patient geometry, thereby contributing to higher doses in larger individuals.

In contrast, vertical positioning relative to the scanner’s isocenter showed no statistically significant effect on radiation dose or X-ray tube exposure settings in our cohort. Although patients positioned at the isocenter exhibited less variability in dose, this did not translate into a meaningful reduction in exposure, suggesting that—within routine abdominal protocols—minor positioning inaccuracies may play a limited role compared to patient size.

These findings support the need to incorporate patient body geometry—not only BMI or weight—into CT dose optimization strategies. Even in patients with normal BMI, a larger cross-sectional width in the scanned region may require individualized protocol adjustments to avoid unnecessary radiation. The integration of patient-specific metrics, automated exposure modulation, and positioning aids may contribute to more consistent image quality and improved radiation safety in routine practice.