Microdosimetry assessment of the radiochemical element 177Lu in the treatment of metastatic prostate cancer of the LNCaP cell line

Objective: The aim of our study is to optimize the dose to develop a new treatment protocol for prostate cancer with 177Lu in order to reduce the irradiation of surrounding organs at risk. Methods: A cell line, LNCaP, was used as a target for 177Lu irradiation at the cellular level. A simple linear quadratic model implemented in the MIRDcell software was chosen to describe the survival probability of cancer cells. Results: Our model was established with an activity range per cell of 0.01 to 0.62 Bq/cell corresponding to an absorbed dose of 2 to 125 Gy respectively. However, 0.3 Bq/cell approximately 62 Gy seemed to be the most acceptable planning as it corresponds to 7.4 GBq/cycle, the typical value delivered at 100% of tumor cell coverage. Indeed, a cellular energy distribution yields a self-dose of S(N<--N) = 1.35E-03 Gy/Bq·s, indicating that the nucleus absorbs more energy. Cellular absorption is much lower than that of the nucleus, with S (C<--C) = 1.68E-04 Gy/Bq·s. A portion of the energy is deposited in the cytoplasm, and energy is transferred between the cytoplasm and the nucleus, with S (N <--Cy) = S (Cy<--N) = 1.30E-04 Gy/Bq·s. The membrane cell contributes less to the cellular dose, with S(N<--CS) = 1.30E-04 Gy/Bq·s. Conclusion: This study shows the necessity of a personalized pre-treatment dosimetry to deliver an optimal lethal dose to tumor cells. Keywords: LNCaP cell line, 177Lu, linear quadratic, MIRDcell