Comparison of liver reserve capacity before and after carbon-ion radiotherapy for liver tumors using 99mTc-GSA scintigraphy

[Objectives]99mTc-GSA scintigraphy is performed for patients before and after carbon-ion radiotherapy (CIRT) for liver tumors in our hospital. It is essential to estimate liver reserve capacity and follow up post-CIRT value in order to perform safe and effective CIRT. However, there is currently no established imaging biomarker for assessing liver reserve capacity prior to CIRT for liver tumors. The aim of this study was to compare liver reserve capacity before and after CIRT whether pre-CIRT 99mTc-GSA scintigraphy could accurately estimate the liver reserve capacity.[Methods]Twelve patients (9 males, 3 females) who received 99mTc-GSA scintigraphy imaging before CIRT and the other twice examinations (first post-CIRT and second post-CIRT) during 3-18 months after CIRT were enrolled in this investigation. The median age of patients was 74 (range, 62 to 80) years old. After intravenous injection of 185 MBq of 99mTc-GSA, dynamic and SPECT imaging were performed using a gamma camera. The maximal GSA removal rate (GSA-Rmax), GSA-Rmax of the estimated residual liver after CIRT (GSA-RL) were calculated by applying 99mTc-GSA dynamics of heart and liver to a five-compartment model. GSA-RL before CIRT and GSA-Rmax after CIRT were compared to assess the clinical utility of 99mTc-GSA scintigraphy.[Results]The median GSA-RL before CIRT and GSA-Rmax of first post-CIRT (3-12 months after CIRT), GSA-Rmax of second post-CIRT (6-18 months after CIRT) were 0.430 (range, 0.203 to 0.699), 0.328 (range, 0.168 to 0.611), 0.463 (range, 0.190 to 0.641) mg/min, respectively (n.s., between GSA-RL and GSA-Rmax of first post-CIRT, GSA-RL and GSA-Rmax of second post-CIRT, Wilcoxon signed-rank test applying Bonferroni correction). The first post-CIRT examination showed a slight decrease in liver reserve capacity, probably reflect mild subacute liver damage by CIRT, while it was recovered to the initially estimated value at the second post-CIRT examination. There was no significant difference in comparison with estimated liver reserve capacity before CIRT and actual value after CIRT in patients with liver tumors.[Conclusions] 99mTc-GSA scintigraphy was useful for the estimating and follow-up assessment of liver reserve capacity for safe CIRT procedure. GSA-RL before CIRT would be a promising imaging biomarker to estimate liver reserve capacity after CIRT, especially the second post-CIRT examination tended to be more consistent with the estimated value.SNMMI 2021 Annual Meetin