(OA35) Impact of Staging 68Ga-PSMA-11 Pet Scans on Radiation Treatment Plans in Patients With Prostate Cancer

Abstract

Gallium-68-labeled Prostate Specific Membrane Antigen (68Ga-PSMA-11) PET has superior sensitivity and specificity for detecting lymph node and bone metastases from prostate cancer compared to conventional CT/MRI or bone scan, and may allow physicians to individually tailor radiation treatment (RT) plans. The majority of literature to date evaluates 68Ga-PSMA-11 PET in the setting of biochemical recurrence; there is a relative paucity of data assessing the impact of staging 68Ga-PSMA-11 PET imaging. Patients who underwent 68Ga-PSMA PET imaging prior to definitive treatment for prostate cancer between December 2015 and December 2016 at our institution were included. Changes in RT plans were based on our institutional policy of boosting PSMA-avid lymph nodes with consideration for treating paraaortic nodes in those with pelvic nodal involvement. Forty-five patients were included in this analysis. Median age was 70 years (IQR 66-74 years). The majority of patients had high-risk disease by Gleason score (Gleason score 8-10 in 32 patients (71%)) and CAPRA score (36 patients (80%)). All patients had 68Ga-PSMA PET uptake in the prostate. 26 patients (58%) had N1 disease on 68Ga-PSMA PET scan; 21 (47%) were previously N0. Six patients (13%) had bone metastases on 68Ga-PSMA PET scan; four (9%) had prior negative bone scans. 68Ga-PSMA PET identified new N1 or M1 disease in 25 patients (56%). 22 (49%) RT plans were adjusted based on 68Ga-PSMA PET results; 15 patients (33%) received an involved nodal boost with inclusion of paraaortics, 4 patients (9%) underwent nodal boost only. 4 patients (9%) underwent focal radiation to five bone lesions. Patients with RT changes were more likely to be on long-term ADT (95% vs. 70%, p = 0.047), primarily due to identification of new nodal metastatic disease. Three patients (7%) were switched from short term to long-term ADT due to identification of new nodal involvement on 68Ga-PSMA PET scan. 68Ga-PSMA PET imaging identified new N1 or M1 disease in the majority of patients, with RT changes in 49% of patients. Prospective investigation is needed to clarify the role of 68Ga-PSMA PET imaging for staging and RT planning, as well to evaluate the clinical benefit of subsequent RT changes.