Individual differences in internal dose from 99mTc-GSA hepatic scintigraphy

1. IntroductionTc-99m-galactosyl human serum albumin (99mTc-GSA) is a molecular imaging agent used for evaluation of hepatic function. Fifty-one patients have experienced 99mTc-GSA scintigraphy at QST Hospital in Japan from Dec. 2018 to Nov. 2019. Their imaging data are beneficial for inspection before and after receiving radiation therapy. In order to assist the medical professionals in dosage indications as well as medical exposure perspective, this study focuses on providing individual dose assessment over the liver and heart in 99mTc-GSA examination. Such information can be used for comparing the difference in dose absorption of a certain population of elderly patients with liver disorders. 2. MethodsThere were 51 patients involved in the study, generating 62 data files as some patients were scanned twice on distant dates. Clinical images were taken as dynamic scan of 30 seconds/frame in a duration of 31.5 minutes, followed up by whole-body scan using a gamma camera (Siemens E.cam Signature Series) after 99mTc-GSA injection of 123.3-305.9 MBq. Since the data of whole-body scan was obtained shortly after the dynamic protocol, this was used to determine the radiation activity (MBq) of liver against whole body at 31.5-minute mark. By dividing the counts in liver during the same period for its activity, camera sensitivity (cps/Bq) or the count rate per Bq of uptake in organs for individual patient was acquired. The cumulated counts in the contoured liver and heart region were then converted into approximate disintegrations by applying this sensitivity value. The number of decays occurred is an essential input data to calculate the particular absorbed dose for each patient. 3. Results and discussionStatistical data of the total disintegrations for 31.5 minutes per unit intake were summarised, showing a significant difference among patients. As for liver, the number of decays mostly ranges from 500 to 1000 in 47 over 51 patients, or 92% of the population. As for heart, this number is much lower, ranging mostly from 25 to 150 in 45 over 51 patients or 88% of the population. This trend of high concentration of radioactivity in liver compared to heart is in agreement with most 99mTc-GSA studies. This presentation will provide further results on the individual differences in internal doses calculated using OLINDA/EXM.日本保健物理学会第53回研究発表