Radioprotection No. 60-1 | Page 75

H. Murat et al.: Radioprotection 2025, 60( 1), 65 – 75 69

Table 2. Internal dose assessment for whole body 18 F-FDG PET examinations.

examinations are presented in Table 5, showing significant differences in LAR between the gender. It has been observed that women have a slightly increased risk of developing cancer when exposed to radiation compared to men. Further analysis reveals that the LAR for bladder, lung, stomach, and liver cancer vary significantly between genders. However, there were no significant differences found between men and women in relation to brain, kidney, colon, red bone marrow( RBM), and thyroid cancer.

Figure 2 illustrates the adjusted of LAR from the BEIR VII phase II report using 3 rd order polynomial approach. This figure shows how the LAR of cancer incidence due to PET examinations varies as a function of age at exposure for different genders and organs. It is already known that LAR is an important metric for cancer risk assessment associated with low-dose radiation exposure. It consists of two components:( 1) the radiation dose received from the imaging procedure and( 2) its potential long-term effects on cancer. In this study, LAR values for organs such as RBM, stomach, bladder, and colon are higher in men than women of similar age of exposure. However, LAR for kidneys and brain tend to be higher in women than men.

4 Discussion

The current principles on radiation protection emphasizes that the use of radiation must be justified by a clear net benefit. The principle also applies to PET / CT examinations, ensuring that the benefits to a patient from the examinations are greater than any potential risks involved. Examinations satisfying this criterion are considered clinically necessary. Typically, professional judgment is essential in weighing the“ benefits” against the“ radiation risks”, which can be difficult to compare directly. The determination of clinically indicated examinations requires professionals with expertise in both the effects of ionizing radiation and the clinical advantages of nuclear medicine. Nevertheless, it is crucial to have a clear understanding of the magnitude of risk a patient is exposed to during a particular examination. Moreover, it is crucial to understand how these risks vary depending on factors such as age at exposure, gender, and the amount of radiation exposure from nuclear medicine procedures. The findings of this study offer valuable insights into these factors for patients who are undergoing whole-body PET / CT examinations using 18 F-FDG radiotracer.

This study reported three important findings from the patient organ dose, effective dose, and LAR of cancer incidence. We assessed the effective dose for both the PET and CT components, along with the corresponding organ cancer risk for the PET component only. We focused on assessing the organ dose from the PET component, and we acknowledge the significance of considering additional external exposure from the CT component in comprehensive cancer risk evaluations. However, because of limited data from CT and the specific objectives of this study, which aimed to isolate the direct contributions of the internal exposure from PET component to the overall radiation burden, the CT component was not included in our organ dose analysis. This approach likely underestimates the total patient risk, as the CT component exposes patients to relatively higher doses that significantly contribute to organ cancer risk. We utilized IDAC-Dose 2.1 to calculate the organ and effective doses for patients undergoing whole-body 18 F-FDG PET / CT examinations. Table 3 in the results section indicates that the mean dose from the CT component is nearly 50 % higher than that from PET( Alameen et al., 2021; Andersson et al., 2017a; Masoomi et al., 2020). Consequently, it can be inferred that the patient cancer risk associated PET / CT examinations could be approximately 50 % higher than the estimates provided in this study.

The variation in absorbed doses across different organs can be attributed to the differential uptake and metabolism of 18 F- FDG. In this study, the bladder exhibits the highest radiation dose at 23.483 mGy, which is significantly higher than other organs. This relatively higher dose can be attributed to the metabolic and excretory pathways of 18 F-FDG, which accumulate in the urinary tract( Quinn et al., 2016). The brain follows with a dose of 15.244 mGy, likely due to its high glucose uptake and metabolism, which is a characteristic behavior of 18 F-FDG as a glucose analog( Boellaard et al., 2015). Murat et al.( 2023) reported high bladder doses, but with a slightly lower average, suggesting potential variations in scanning techniques( Murat et al., 2023). The high dose in the brain aligns with previous findings, which similarly highlighted the brain’ s high metabolic activity and resultant dose concentrations( Breustedt et al., 2018; Grimes & Celler, 2014; Masoomi et al., 2020).

Table 3 clearly shows that the mean E for PET / CT examinations in this study is 20.09 ± 7.85 mSv, which could be lower than the values reported in previous studies( Alameen et al., 2021; Huang et al., 2009; Kessara et al., 2023a; Khamwan et al., 2010; Salah et al., 2020). Noting that, the ratio of E to A is 1.61 10 �2 mSv / MBq is compliant with the recommendations of the International Commission on Radiological Protection( ICRP, 2008). These findings consistent with prior studies that suggest CT is a major contributor to the overall E in PET / CT scans( Alameen et al., 2021; Andersson et al., 2017a; Khamwan et al., 2010; Masoomi et al., 2020; Salah et al., 2020). Additionally, it has been established that radiation dose observed in CT scans is indicated by the CTDI vol and DLP values. In this study, the imaging protocol used may have a significant impact on the CTDI vol and DLP, as higher tube currents and longer scan