Influence of dosimetry method on bone lesion absorbed dose estimates in PSMA therapy: application to mCRPC patients receiving Lu-177-PSMA-I&T

Abstract Background Patients with metastatic, castration-resistant prostate cancer (mCRPC) present an increased tumor burden in the skeleton. For these patients, Lutetium-177 (Lu-177) radioligand therapy targeting prostate-specific membrane antigen (PSMA) has gained increasing interest promising outcome data. Patient-individualized dosimetry enables improvement of success aim minimizing absorbed dose to organs at risk while maximizing tumors. Different dosimetric approaches varying complexity and accuracy exist for this purpose. The Medical Internal Radiation Dose (MIRD) formalism applied tumors assumes a homogeneous activity distribution sphere unit density derivation S values (TSV). Voxel value (VSV) can account heterogeneous activities but are simulated specific tissue. Full patient-individual Monte Carlo (MC) simulation addresses both, distributions. Subsequent CT-based weighting potential overcome assumption MIRD TSV VSV methods, which could be major limitation application bone metastases density. investigation is comparison methods lesion mCRPC patients receiving Lu-177-PSMA therapy. Results In total, 289 lesions 15 were analyzed. Percentage difference (PD) average per compared MC, averaged over all lesions, was + 14 ± 10% (min: ? 21%; max: 56%) TSVs. With lesion-individual using Hounsfield Unit (HU)-to-density conversion on patient’s CT image, PD reduced 8 1% 10%; 3%). voxel level three-dimensional (3D) voxel-wise lesion, revealed large PDs 18 11% 27%; 58%) soft tissue approach MC; after correction, 5 12%; 2%). Conclusion Patient-individual MC capable densities lesions. Since computational effort prevents its routine clinical application, or used. This study showed necessity dosimetry.