Radioprotection No. 60-1 | Page 72

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

Table 1. Demographic of 40 subjects( men and women) included in this study. Patient characteristics Gender( Mean ± SD,( Min � Max))

Men( n = 20) Women( n = 20)

exposed to during a PET / CT examinations. Additionally, it is important for patients undergoing PET / CT to be informed about their radiation dose and the potential risk of long-term development of cancer. The introduction of radiation dose quantities, such as effective dose( E), has allowed for the communication of information regarding radiation levels among medical staff and public( ICRP, 2021, 2022). The E is the most frequently used for estimating the relationship between radiation and stochastic effects, regardless of the type of exposure. The quantity reflects the health impact of radiation exposure on both radiation workers( aged 18 – 65) and the public regardless of age and gender. Significant gender and age at exposure differences have been recognized as key factors contributing to variations in potential cancer risk related to radiation exposure( Harrison et al., 2016; ICRP, 2007). However, the E concept has been questioned due to its lack of consideration for age at exposure and gender factors( Brenner, 2012). Researchers have proposed Lifetime Attributable Risk( LAR) of cancer incidence as ultimate output to the E, concentrating on estimating cancer incidence from radiation across various age at exposure and genders( Andersson et al., 2017a; Huang et al., 2009; Karim MKA et al., 2017; National Research Council, 2006).

In nuclear medicine, LAR could be used to assess radiation-related health risks. It quantifies the risk of cancer incidence per 100,000 persons exposed to a single dose of 0.1 Gy. This method utilizes a risk model derived from epidemiological studies such as excess relative risk( ERR) and excess absolute risk( EAR). ERR represents the relative increase in cancer rates in an exposed population compared to an unexposed population, while EAR measures the additional absolute risk of developing cancer due to exposure over a specified period. These models are applied in presenting the foundation of the linear non-threshold( LNT) model into practical in epidemiological studies. In the LNT model, there is no threshold dose below which the risk is eliminated. These estimates are important for understanding the specific risks associated with radiation doses used in PET / CT examinations( National Research Council, 2006). The significance of LAR is highlighted in the BEIR VII phase II report, published in 2006 by the United States National Research Council Committee. This report focused on determining the risks of exposure to low levels of ionizing radiation drawing on data from the life span study of atomic bomb survivors( Karim MKA et al., 2017; National Research Council, 2006). This approach was notably reflecting its relevance and application in evaluating radiationrelated health risks( Fahey et al., 2016; Huda et al., 2011; Karim MKA et al., 2017; Murat et al., 2023).

The LAR method can predict cancer risk generated from different variables such as gender, age at exposure, and absorbed dose. However, there are relatively few studies based on LAR has focused on PET / CT examinations. Furthermore, past studies indicated that there is absence of age-specific LAR coefficients in the BEIR VII Phase II report for adjacent age at exposure groups, necessitating the use of an interpolation method( Halid et al., 2018). This interpolation method which is a type fitting method is useful for bridging gaps in the data, inherently introduces a degree of uncertainty( Kessara et al., 2023). This limitation underscores the need for cautious interpretation of interpolated risk, especially when utilizing risk assessments. Therefore, this study aimed to evaluate organ doses and LAR of cancer incidence risk associated with wholebody 18 F-FDG PET / CT examinations.

2 Materials and methods

2.1 Subjects demography

This retrospective study was conducted at a one oncology center in the Klang Valley, with approval from the Research and Ethics Committee( identification number NMRR- 18-1176-41991). Informed consent was waived for this study. A total of 40 individuals participated in whole-body 18 F-FDG PET-CT examinations. Only those patients who had imaging records at the center were included in the analysis, resulting in a final sample size of 20 men and 20 women. The sample has a median age at exposure of 55 years, and an age at exposure range spanning from 17 to 85 years. All data collection and processing were done in accordance with institutional ethical standards. The data collected comprised of administrated activities, A, in megabecquerel( MBq), volume weighted CT dose index( CTDI vol), dose length products( DLP), as well as patient age, gender, weight and height.

Table 1 presents the characteristics of both men and women participants in this study. Men had an average age of 54 years, with a standard deviation of 15 years and a range of 23 to 85 years, while women had an average age of 53 years, with a standard deviation of 14 years and a range of 17 to 75 years, suggesting that there is a similar age distribution in both groups. It has been found that, on average, women tend to have slightly higher Body Mass Index( BMI) values than men. This can lead to an increased requirement for administered activity of radiopharmaceuticals to achieve sufficient image quality, resulting in higher radiation exposure( Halpern et al., 2004). Furthermore, higher BMI values may lead to attenuation of the emitted radiation, which can affect image quality and require