Correlation between longitudinal dosimetry and PET follow-up as indicator for salivary gland toxicity after Lu-177-PSMA therapy

Ziel/Aim: Xerostomia is a relevant side effect of Lu-177-PSMA therapy for advanced prostate cancer. The first aim of this study was to evaluate the longitudinal salivary gland dosimetry over multiple cycles. The second aim was to investigate whether PSMA-PET/CT can be used to predict the salivary gland absorbed dose during the course of treatment.

Methodik/Methods: 23 patients with metastasized castration-resistant prostate cancer were included. 5/23 patients received 6 cycles of Lu-177-PSMA-I&T therapy, and 19/23 underwent 4 cycles (mean: 7.6 GBq/cycle). Whole-body SPECT/CT imaging was performed at 24, 48, and 72 h after each therapy. F-18-PSMA-1007 PET/CT images (mean: 0.22 GBq) were acquired before the first, third and fifth therapy cycle. Parotid (PG) and submandibular glands (SG) were segmented in PET and SPECT scans (24 h) using PETedge+in MIM. Dosimetry was performed using MIM SurePlan MRT with a mono-exponential fit model.

Ergebnisse/Results: Mean absorbed doses for cycles 1 to 6 were: SG: 0.24±0.13 Gy/GBq, 0.27±0.19 Gy/GBq, 0.25±0.16 Gy/GBq, 0.24±0.15 Gy/GBq, 0.25±0.13 Gy/GBq, and 0.24±0.10 Gy/GBq; PG: 0.32±0.14 Gy/GBq, 0.37±0.17 Gy/GBq, 0.35±0.15 Gy/GBq, 0.32±0.15 Gy/GBq, 0.45±0.14 Gy/GBq, 0.30±0.14 Gy/GBq. No significant differences were observed between cycles (SG: p>0.07; PG: p>0.06). A strong correlation was observed between the salivary gland uptake in PET and the salivary gland absorbed dose for the pre-therapy PET and the first cycle (SG: r=0.63, p<0.001; PG: r=0.78, p<0.001), as well as the follow-up PET before the third cycle and the dosimetry after the third cycle (SG: r=0.66, p<0.001; PG: r=0.61, p<0.001). In 20/23 patients, PET follow-up and longitudinal dosimetry showed consistent uptake trend, with 18/20 demonstrating stable PET uptake and absorbed dose.

Schlussfolgerungen/Conclusion: This analysis indicates that F-18-PSMA-1007 PET/CT may be suitable for estimating the salivary gland absorbed dose during the course of Lu-177-PSMA-I&T therapy.

Publikationsverlauf

Artikel online veröffentlicht:
12. März 2025