Estimation of kidneys and urinary bladder doses based on the region of interest in (18)fluorine-fluorodeoxyglucose positron emission tomography/computed tomography examination: a preliminary study

BACKGROUND: Kidneys and urinary bladder are common physiologic uptake sites of 18fluorine-fluorodeoxyglucose ((18)F-FDG) causing increased exposure of low energy ionizing radiation to these organs. Accurate measurement of organ dose is vital as (18)F-FDG is directly exposed to the organs. Organ dose from (18)F-FDG PET is calculated according to the injected (18)F-FDG activity with the application of dose coefficients established by International Commission on Radiological Protection (ICRP). But this dose calculation technique is not directly measured from these organs; rather it is calculated based on total injected activity of radiotracer prior to scanning. This study estimated the (18)F-FDG dose to the kidneys and urinary bladder in whole body positron emission tomography/computed tomography (PET/CT) examination by comparing dose from total injected activity of (18)F-FDG (calculated dose) and dose from organs activity based on the region of interest (ROI) (measured dose).

METHODS: Nine subjects were injected intravenously with the mean (18)F-FDG dose of 292.42 MBq prior to whole body PET/CT scanning. Kidneys and urinary bladder doses were estimated by using two approaches which are the total injected activity of (18)F-FDG and organs activity concentration of (18)F-FDG based on drawn ROI with the application of recommended dose coefficients for (18)F-FDG described in the ICRP 80 and ICRP 106.

RESULTS: The mean percentage difference between calculated dose and measured dose ranged from 98.95% to 99.29% for the kidneys based on ICRP 80 and 98.96% to 99.32% based on ICRP 106. Whilst, the mean percentage difference between calculated dose and measured dose was 97.08% and 97.27% for urinary bladder based on ICRP 80 while 96.99% and 97.28% based on ICRP 106. Whereas, the range of mean percentage difference between calculated and measured organ doses derived from ICRP 106 and ICRP 80 for kidney doses were from 17.00% to 40.00% and for urinary bladder dose was 18.46% to 18.75%.

CONCLUSIONS: There is a significant difference between calculated dose and measured dose. The use of organ activity estimation based on drawn ROI and the latest version of ICRP 106 dose coefficient should be explored deeper to obtain accurate radiation dose to patients.