A Prospective, Multinational Comparison Of Multi-Parametric And Whole Body Magnetic Resonance Imaging (Mp-Mri And Wb-Mri) F-18 Fluoro-Methyl-Choline (Fch) And Ga-68 Hbed-Cc-(Psma) In High Risk Men Being Considered For Salvage Radiation Treatment For Biochemical Failure Post Radical Prostatectomy: Detection Rates, Management Impact And Treatment Response.

458 Introduction: Men presenting with rising PSA following radical prostatectomy (RP) may be cured by salvage radiotherapy (SRT). However, a significant proportion of men will not benefit from SRT, more frequently in those with high risk features. Imaging options such as FCH and PSMA PET/CT, and MRI may better identify men who will best benefit. The aim of this study was to evaluate the predictive value of new methods of imaging in triaging men unlikely to benefit from SRT despite negative or equivocal conventional imaging. Methods: Prospective, multisite, international trial in men post RP with negative or equivocal conventional imaging, high risk features (PSA > 0.2ng/ml and >GSC 7 or PSA DT 1.0ng/ml) and rising PSA being considered for SRT . 91 eligible enrolled men underwent FCH PET/CT, mp-MRI and WBMRI within 2 weeks, with additional PSMA in (31/91). All imaging was double read. Treatment plan was documented before and after imaging to assess management impact, and all subsequent treatments, biopsies and serial PSA collected. Imaging results were validated using a composite reference standard. Treatment response was defined as a PSA drop of > 50% in response to SRT in the absence of ADT. Results: Median PSA at imaging 0.41±1.2, median Gleason score 8, median PSA doubling time 5.0 months. By modality, detection rates for any recurrent PCa were (24/89)27%, (29/91)32% and (13/31)43% for mp-MRI, FCH and PSMA respectively (WBMRI reported separately). In men with positive scans, extra-fossa disease was identified in (11/24) 41% (mpMRI), (17/29) 58% (FCH) and (9/13) 69% (PSMA). Comparing PSMA and FCH imaging, PSMA identified 36 sites of disease (13/30 men) compared to 20 (13/30 men) on FCH (p < 0.005). Imaging findings changed expected management in 46% (42/91) due to FCH, and 23% (21/90) MRI. PSMA provided incremental management change in 7/31 (23%) over FCH. Treatment response to SRT ((fossa +/- regional nodes) was 33/45 (72%) (negative or fossa confined) FCH vs. 3/9 (33%) with extra-fossa +ve FCH (p< 0.03), 7/8 (87%) (negative or fossa confined) PSMA vs, 1/7(14%) extra-fossa +ve PSMA (p<0.009). Conclusions: A high incidence of extra-prostatic disease was identified with FCH, PSMA and MRI in high risk men with (negative conventional imaging) rising PSA post RP being considered for salvage radiotherapy. This had a consequent high management impact and significant effect on treatment response, with the highest response in men with negative or fossa-confined disease on PET/CT.