Main Session
Sep 30
PQA 07 - Genitourinary Cancer, Patient Safety, Nursing/Supportive Care

3219 - Impact of PSMA PET/CT on Initial Staging and Definitive Radiation Therapy Planning in Prostate Cancer

12:45pm - 02:00pm PT
Hall F
Screen: 11
POSTER

Presenter(s)

Omar Awad, MD, MS Headshot
Omar Awad, MD, MS - Baylor College of Medicine, Houston, TX

R. O. Elsaka1, M. E. Kotb2,3, A. M. Eldrieny4, M. I. Morsi5, M. H. E. D. Khalifa6,7, A. M. Eltelbany8, O. Awad1,9, Y. A. Abdelaziz10, H. M. Hegazy11, and A. A. ElSaid12; 1Clinical Oncology Department, Faculty of Medicine, Alexandria University, Alexandria, Egypt, 2Radiological Sciences and Medical Imaging Department - Pharos University, Alexandria, Egypt, 3SUN Oncology Center, Alexandria, Egypt, 4Faculty of Applied Health Sciences Technology, Pharos University in Alexandria, Alexandria, Egypt, 5Radiation Sciences department - Medical Research Institute, Alexandria, Egypt, 6Alexandria University Clinical Oncology Department, Alexandria, Egypt, 7University of Alexandria, Alexandria, Egypt, 8Cancer Management and Research Department, Medical Research Institute, Alexandria, Egypt, 9Department of Radiation Oncology, Dan L. Duncan Comprehensive Cancer Center, Baylor College of Medicine, Houston, TX, 10Alexandria University, Alexandria, Egypt, 11Clinical Oncology and Nuclear Medicine Department- Alexandria University, Alexandria, Egypt, 12Clinical Oncology and Nuclear Medicine Department, Alexandria University, Alexandria, Egypt

Purpose/Objective(s):

The integration of 18F-choline PSMA PET/CT imaging in the initial staging and radiotherapy (RT) planning of prostate cancer is evolving. This study aims to compare risk stratification, target volumes (TV) definition, and dosimetric parameters between RT plans based on standard imaging (CT/MRI + bone scan) and PSMA PET/CT-based imaging.

Materials/Methods:

This retrospective study included newly diagnosed prostate cancer patients treated with definitive RT at SUN Oncology Center, Alexandria, Egypt, from January 2019 to December 2022. All patients underwent 18F-choline PSMA PET/CT in addition to standard imaging workup (CT abdomen/pelvis and/or MRI pelvis, bone scan). We evaluated initial staging and TV definitions based on both imaging modalities. In cases where TV differed, two RT plans were generated for each patient:

1. Standard imaging based RT plan

2. PSMA PET/CT based RT plan

Both plans were compared for TV changes and dose-volume histogram (DVH) parameters, including organs at risk (OAR) doses. RT planning was performed using IMRT or VMAT on the treatment planning system to a dose up to 78 Gray (Gy), 2 Gy/fx.

Results:

75 patients were analyzed, with a mean age of 69.6 ± 8.1 years and a median prostate volume of 60.3 cc (IQR: 44.2–87.8). Among them, 50.7% had a Gleason Score (GS) of 7, while 26.6% had GS 8-10. Standard imaging detected locoregional disease in 80%, N1 in 12%, and M1 in 8%, while PSMA PET/CT identified locoregional disease in 60%, N1 in 24%, and M1 in 16%. Staging was altered in 48% of patients, with 5 down-staged, 31 upstaged, and 12 newly identified with distant metastases. TV adjustments were required in 34.7% of cases based on PSMA PET/CT findings.

PSMA PET/CT-based RT plans delivered significantly higher doses to OARs. Rectum V60% was 19.96% vs. 18.1% in standard imaging-based RT plans (p=0.024), and rectum V50% was 30.92% vs. 28.27% (p=0.019). The maximum femur dose (Dmax) was 46.3Gy in PSMA based RT plans, compared to 41.9Gy in standard imaging-based plans (p=0.006). The maximum bowel dose was 54.7Gy vs. 46.3Gy (p=0.014). Patients who were upstaged had significantly larger prostates (77.5 ± 34.8cc vs. 59.8 ± 30.6cc; p = 0.026). Although mean pretreatment PSA values were higher in upstaged patients (43.2 ± 55.3 vs. 24.3 ± 20.9ng/mL), the difference was not statistically significant (p = 0.07). Stage migration was more frequently observed in patients with GS = 8.

Conclusion:

PSMA PET CT significantly impacts initial staging and RT planning, leading to stage modifications in 48% of cases and changes in TV definition in 34.7%. It also identifies more N1 and M1 disease, increasing radiation doses to OARs. Patients with larger prostates, higher GS, and elevated PSA levels are more likely to undergo stage migration, supporting the routine use of PSMA PET/CT in prostate cancer RT planning.