The influence of 68Ga-prostate-specific membrane antigen PET/computed tomography on prostate cancer staging and planning of definitive radiation therapy

Objectives Prostate-specific membrane antigen (PSMA) PET/computed tomography (CT) is a novel imaging tool with an evolving role in the management of prostate cancer. This study aims to retrospectively evaluate the impact of Ga-68-PSMA PET/CT on prostate cancer staging and definitive radiation therapy planning. Methods Between April 2015 and June 2020, 366 men with prostate cancer were evaluated with Ga-68-PSMA PET/CT. Of these, 108 patients had PSMA PET/CT before radiation therapy. Radiation was given as primary treatment in 58 (54%) and as salvage radiation therapy for biochemical recurrence after primary surgery in 50 (46%) patients, respectively. Patient and disease characteristics were analyzed, and impact of PSMA PET/CT on disease staging and radiotherapy planning was evaluated in comparison to conventional imaging. Results Median age at presentation was 69 years, and median prostate-specific antigen was 18 ng/mL (3.6-400) for primary and 0.4 ng/mL (0.1-4.6) for salvage radiation, respectively. The combined change of disease stage rate was 36% (39/108) with 45% (26/58) in the subgroup of primary radiation and 26% (13/50) in the patients intended for salvage radiation. Upstaging was found in 24 (22%) and downstaging in 15 (14%) patients. Radiation planning was changed based on PSMA PET/CT in 34 (31%) patients, including 7 (6.4%) patients in which stereotactic body radiotherapy (SBRT) was added to oligometastatic sites. The radiation field was extended to include pelvic lymph node involvement in 21 patients. Conclusions Ga-68-PSMA PET/CT changed the prostate cancer stage in around one-third of men. PSMA PET/CT significantly impacted radiation planning. Further prospective studies are still required.