Absorbed doses from cross-fire to solid organs in 300 patients undergoing therapy with 177Lu-octreotate

Objectives Fractionated therapy with 177Lu-octreotate has been reported to be an effective treatment option for patients with generalized neuroendocrine tumors. The aim of this study was to calculate the contribution from cross fire for solid organs (kidneys, liver and spleen) in an individualized dosimetry protocol.

Methods A total of 148 female and 152 male patients with neuroendocrine tumors with high somatostatin receptor expression (grade 3 or 4) were included. After infusion of 7.4 GBq of 177Lu-octreotate, planar whole body images and SPECT/CT over the abdomen were acquired at 24, 96 and 168 h after infusion. Absorbed dose originating from the organ itself (self-dose) to solid organs was calculated based on pharmacokinetic data obtained from SPECT/CT. Absorbed dose originating from other organs (cross-dose) was based on organ-based analysis of planar whole body images using cross-fire dose factors from Olinda/EXM 1.1.

Results For a single therapy cycle of 7.4 GBq the percentage of absorbed dose from cross-fire was 1.5 (0.8-2.9) (Median (1:st-3:rd quartiles)) for the right kidney, 1.6 (0.8-3.2) for the left kidney, 1.4 (0.9-2.0) for the liver and 0.8 (0.6-1.3) for the spleen. Self-doses to solid organs may have been slightly over-esimated since SPECT images were not corrected for scattered radiation. It can also be noted that there were a few patients where the cross-fire to the kidneys exceeded 10% of its total absorbed dose. In those rare cases the patients had a high tumour burden and low uptake in and absorbed doses to the kidneys.

Conclusions The absorbed dose from 177Lu-octreotate to solid organs due to cross-fire is generally so low that it can be neglected.