Comparative dosimetry study of PARaDIM and RT-PHITS with ICRP publication 128: calculation of organ doses from...

This study evaluates organ doses from ¹⁸F-FDG whole-body PET-CT using the phantom-based software PARaDIM and patient image-based software RT-PHITS and compares with reference data from ICRP Publication 128. Absorbed dose coefficients (mGy/MBq) were calculated using ICRP Publication 145 mesh-type phantoms in PARaDIM and 20 patient datasets (10 male, 10 female) from 'The Cancer Imaging Archives' website in RT-PHITS. Organs were segmented in 3D Slicer, and dose coefficients were derived after physical decay correction of the resultant dose rates (mGy/s). The patient cohort (n = 20; 10 males, 10 females) had an average age of 52.1 years, height of 172.1 cm, weight of 76.65 kg, and total administered activity of 306.55 MBq. Absorbed dose coefficients from PARaDIM and RT-PHITS ranged from 0.01 to 0.07 mGy/MBq. RT-PHITS showed acceptable agreement with ICRP 128 and PARaDIM for most organs, except for the urinary bladder and heart wall. Standard deviations (SD) for RT-PHITS urinary bladder doses were 0.04 relative to ICRP 128 and 0.12 relative to PARaDIM; heart wall SDs were 0.016 and 0.014, respectively. Overall, RT-PHITS organ doses yielded an average SD of 0.0073, with the highest deviation in the heart wall. The results indicate that anatomical differences lead to measurable variations between the generalized and individualized dosimetry methodologies. Because a consistent physical decay model of ¹⁸F was used, these variations primarily reflect structural and geometric factors. This study provides a framework for advancing individualized dosimetry approaches and supports future developments in cumulative exposure assessments and potential theranostic applications.