Impact of inter-cycle changes in dose heterogeneity, biokinetics and tumour volume on dose-based personalisation of administered activity for 177Lu-based treatment

In this study, we used both rigid and deformable image registration for each clinical case to register the 4 sequential SPECT/CT scans in the same frame of reference of the first CT scan. Dose rate images were calculated for each time point from the SPECT activity images using a local energy deposition (LED) approach. A voxel-by-voxel fit to an mono-exponential expression was then applied to the aligned dataset to obtain the clearance half-time for each voxel, and the absorbed dose calculated by analytical integration. Once the physical indices of spatial absorbed dose distribution were computed, the radiobiological metrics of BED and EUD were calculated at the voxel and organ level respectively[5]. In this study, there is considerable deviation between the predicted intra-cycle kidney absorbed dose per AA and those calculated based on the SPECT/CT data. The intra-cycle kidney pharmacokinetics as quantified by the effective half-life increased 30% between cycles 1 and 4 while the heterogeneity of the dose distribution changed significantly within each cycle based on the EUD radiobiological metric. Patient-specific dosimetry simulations based on data from previous multi-cycle Lu177-DOTATATE clinical study demonstrate the importance of consider changing intra-cycle dose heterogeneity, tumour volume and kidney biokinetics in personalising patient administered activity. his study shows understanding the correlation between changes in biology and absorbed dose could help improve t...
Source: Journal of Nuclear Medicine - Category: Nuclear Medicine Authors: Tags: Dosimetry Source Type: research