Impact of PSMA PET/CT on initial staging and planning of definitive radiation therapy in prostate cancer

Abstract

OBJECTIVES: comparing risk grouping, target delineation, and dosimetric parameters between RT plans based on conventional imaging (CT and/or MRI pelvis with bone scan) versus 18F-PSMA PET/CT in the same patients. METHODS: A 75 newly diagnosed PCa patients treated with definitive RT between January 2019 and December 2022 at our center were included. Each underwent standard imaging and 18F-PSMA PET/CT. Two RT plans were generated; one from conventional imaging and another from PSMA PET/CT data using IMRT or RapidArc on the Eclipse (Varian, USA) system. Plans were compared regarding target volumes (TVs), dose-volume histograms (DVH), and doses to organs at risk (OARs). RESULTS: Mean age was 69.6 ± 8.1 years, and mean pretreatment PSA was 33.47 ± 42.05 ng/mL. Gleason score (GS) was 7 in 50.7% and 8-10 in 26.6%. PSMA -PET/CT altered TVs in 26 patients (34.7%). PSMA-based RT plans showed significantly higher rectal V60% (19.96% vs. 18.1%, p = 0.024), femoral maximum dose (46.37 Gy vs. 41.98 Gy, p = 0.006), and bowel maximum dose (54.7 Gy vs. 46.3 Gy, p = 0.014). Upstaged patients had larger mean prostate volumes (77.53 ± 34.76 cc vs. 59.76 ± 30.6 cc; p = 0.026). CONCLUSION: 18F-PSMA -PET/CT significantly impacts staging and RT planning in prostate cancer, leading to altered TVs and dosimetry, significantly in patients with larger prostates, but non significantly in patients with GS ≥ 8, and higher PSA levels. ADVANCES IN KNOWLEDGE: PSMA PET/CT meaningfully changes staging, TVs, and dosimetry. It highlights the modality's value in improving accuracy in definitive RT planning.