Author: Nadège Anizan, David Broggio, Désirée Deandreis, Didier Franck, Camilo Garcia, Stéphanie Lamart, Sébastien Leygnac, Alexandre Pignard 👨🔬
Affiliation: Gustave Roussy, Service de Physique Médicale, Institut Bergonié, Service de Physique Médicale, Gustave Roussy, Service de Médecine Nucléaire, Autorité de Sûreté Nucléaire et de Radioprotection (ASNR), PSE-SANTE/SDOS/LEDI, Autorité de Sûreté Nucléaire et de Radioprotection (ASNR), PSE-SANTE/SDOS 🌍
Purpose: This work aimed at developing an innovative workflow for 177Lu-PSMA personalized dosimetry to lesions and organs at risk (OAR) simultaneously, considering the cross-irradiation from bone metastases to red bone marrow, especially for patients with a high skeletal tumor burden.
Methods: Patients were treated for a metastatic castration-resistant prostate cancer with approximately 7.4 GBq of 177Lu-PSMA. Biokinetics in lesions and OAR was assessed using 3 quantitative SPECT/CT images acquired at about 4h, 24h and 6 days post-injection. Segmentation of OAR was performed with an open-source code that uses artificial intelligence on CT. Since bone metastases are often numerous and difficult to identify on CT, they were delineated using an in-house adaptative thresholding algorithm on SPECT/CT images. Absorbed dose was estimated by Monte Carlo simulation in a realistic model of the patient based on segmentations previously described. Cross-fire radiation from bone lesions to red bone marrow was evaluated by computing dose with and without cumulated activity in lesions.
Results: Results were obtained for 405 lesions after the first 177Lu-PSMA cycle of 16 patients. Absorbed doses to lesions ranged from 0.3 Gy to 341 Gy (median: 15 Gy), while dose to kidneys ranged from 1.8 to 6.6 Gy (median: 4.0 Gy) and from 2.2 to 9.2 Gy (median: 3.7 Gy) for parotid glands. In addition, absorbed doses to red bone marrow were between 0.08 Gy and 1.87 Gy (median: 0.22 Gy), and bone metastases cross-irradiation contributed significantly (p-value = 2e-5) from 0.4% to 57% of these dose values.
Conclusion: These results indicate the possibility to perform a comprehensive and personalized computation of absorbed dose to lesions and OAR. Furthermore, this workflow allows consideration of bone lesion contribution to the red bone marrow dose, which might be non-negligible especially in presence of a high skeletal tumor burden as often observed for 177Lu-PSMA patients.