Inter-institutional variability in kidney dosimetry during ¹⁷⁷Lu-DOTATATE therapy in Japan

Dosimetry using SPECT/CT images enables personalized medicine by estimating absorbed doses and optimizing therapy. Differences in organ contouring and calculation algorithms contribute to inter-institutional variability, emphasizing the need for standardization. The present study aimed to investigate factors contributing to inter-institutional variability in kidney dosimetry in Japan. We analyzed four time points in SPECT/CT images of one male and one female patient each from the ¹⁷⁷Lu SNMMI Dosimetry Challenge. Kidney volumes and absorbed doses were calculated at 10 Japanese institutes using their preferred organ-based (OLINDA 2.2, IDAC DOSE 2.1) and voxel-based (Voxel Dosimetry, RT-PHITS, MIM SurePlan MRT, OpenDose3D) software. Reference volumes of interest (VOI) files were distributed to assess the effect of contouring differences on kidney volumes and absorbed doses. Manual VOI contouring revealed substantial inter-institutional variability in kidney volumes, with coefficients of variation (%CVs) up to 16.9%. The reference VOIs reduced volume variability to ≤ 7.4%. Compared to manual VOIs, reference VOIs showed slightly increased doses in both patients with slightly reduced inter-institutional variability. The absorbed doses were generally higher in voxel- than organ-based dosimetry. The %CVs of the right and left kidneys in female patient decreased from 31.36% to 6.26% and 41.28%-3.97%, respectively. Variability in Kidney volume and absorbed doses significantly varied among Japanese institutes. Reference VOIs reduced volume variability but could not fully control dose differences. Voxel-based dosimetry can mitigate inter-institutional variability independent of contouring. Our findings emphasize the importance of algorithm standardization for reliable ¹⁷⁷Lu-DOTATATE kidney dosimetry in Japan.