Towards personalized patient 3D Monte Carlo dosimetry for Lu-177-psma prostate treatments

Abstract

Prostate-Specific Membrane Antigen (PSMA)-labeled Lu-177 therapy is a novel nuclear medicine therapy for metastatic prostate cancer, increasingly adopted worldwide due to the benefits observed in different patient studies. Administered in several cycles, each with a single injection and with a standard activity, the therapy requires customized dosimetry to evaluate efficacy and toxicity. The uptake of Lu-177-PSMA-617 in different organs strongly depends on the patient's anatomy, metastasis distribution, and the activity injected, underscoring the need for personalized dosimetry. This study aims to conduct dosimetry research on patients after several cycles of Lu-177-PSMA administration by Monte Carlo simulation using MCNP6.2. In order to make this study as realistic as possible, a high-resolution anthropomorphic computational phantom is used, the “Mesh-type Reference Computational Phantom” (MRCP) described in ICRP publication 145. This methodology is applied to different distributions of metastatic tissue, based on SPECT images where activity distribution within the patient's body is localized. Since Lu-177-PSMA-617 is deposited in those regions where prostate cancer metastasis has occurred, in Monte Carlo simulations these organs are considered as a source of irradiation with different emission activities probabilities depending on the patient. Once the organ activity distribution is determined, the simulation is performed in MCNP6.2 and the 3D dose distribution in the phantom is evaluated. Based on Monte Carlo results, doses at organs at risk are evaluated, estimating the total absorbed doses until the complete disintegration of Lu-177.Simulation results enable personalized adjustment of injected Lu-177 according to the needs of the clinical case. This approach has proven to be a valuable tool for assessing individual patient doses, treatment effectiveness, and healthy organ irradiation levels.