Bone Marrow and Kidney Doses from Lu-177 Radiopharmaceutical Therapy
Abstract
Purpose
To evaluate the doses to the bone marrow and kidneys from Lu-177 radiopharmaceutical therapy (RPT), as affected by radiopharmaceutical type, cycle of administration, and tumor volume.
Methods
20 patients treated with RPT (13 with Pluvicto, 7 with Lutathera) were chosen for this retrospective study. 9 of the 13 Pluvicto patients received two cycles of injection. A quantitative SPECT/CT was acquired approximately 24 hours post- each injection. 3D dosimetry was performed based on the quantitative SPECT using commercial software (MIM SurePlanMRT v7.4.4) and the Hänscheid Single-Time-Point formulism. Mean doses to kidneys and bone marrow were calculated from AI-derived contours (MIM Protégé). Tumor activities were not excluded. For marrow dosimetry, the whole skeleton was separated into 9 skeletal components. Marrow mean dose was a weighted average of the mean doses to skeletal components, with weightings defined by published active bone marrow concentration in adult skeletons.
Results
Across all patients, average dose to bone marrow from the first cycle of Pluvicto (0.470 ± 0.477 Gy) was higher than from Lutathera (0.179 ± 0.049 Gy), with p = 0.049, while the average dose to the kidneys from Pluvicto (2.151 ± 0.741 Gy) was comparable with Lutathera (2.249 ± 0.391 Gy), with p = 0.704. Comparing cycle 2 with cycle 1 for Pluvicto patients, marrow mean dose decreased by 10.6% and kidneys mean dose increased by 2.9%. Marrow dose from Pluvicto increases with increasing total tumor volume (R² = 0.6437). Dose to kidneys and dose from Lutathera had low correlation with tumor volume.
Conclusion
Pluvicto shows decreasing bone marrow dose and slightly increasing kidney dose in later cycles, as well as higher marrow dose but comparable kidney dose compared with Lutathera. This could be because prostate metastases targeted by Pluvicto are typically in the bone, and tumor uptake was included in dosimetry calculations.