ESTRO 2024 - Abstract Book

S2392

Clinical - Urology

ESTRO 2024

change in treatment that will improve overall survival [1, 2]. The 180°N PSMA PET recurrence trial (Clinicaltrials.gov ID NCT04298112) is a prospective multicenter study where the primary objective is to compare the diagnostic performance of PSMA PET/CT and PET/MRI to multiparametric (mp) MRI for detection of recurrent disease. The patients will be followed 15 years after inclusion. In this analysis, we have investigated how the combined PSMA PET/MRI and PET/CT protocol affected treatment of patients referred as candidates for salvage radiotherapy (sRT) after biochemical recurrence (BCR) in two of the participating hospitals.

Material/Methods:

Patients were recruited from St. Olavs Hospital (Trondheim, Norway) and the University Hospital of North Norway (Tromsø, Norway) from May 2020 to April 2023.All patients had undergone radical prostatectomy (with or without extended pelvic lymph node dissection (ePLND), presented with BCR in accordance with the European Association of Urology and were candidates for loco-regional pelvic salvage radiotherapy based on age and comorbidity. The imaging protocol consisted of MRI (chin to proximal thighs), [68Ga]Ga-PSMA-11 or [18F]-PSMA-1007 PET/CT (vertex to proximal thighs) and PET/mpMRI of the pelvic region, performed sequentially. The PET/CT, PET/mpMRI and mpMRI were evaluated separately by specialists in nuclear medicine and radiology and then in consensus. Imaging recurrence was defined as loco-regional and/or metastatic disease according to consensus. This was compared to corresponding readings of mpMRI only. Change of treatment due to findings on PSMA PET was defined as change from intended treatment for cases where a) consensus imaging findings differed from mpMRI findings and b) this difference resulted in upgrading of disease necessitating other treatment than observation or standard sRT of the prostate bed with or without elective RT of the pelvic region. Differences between groups were assessed by the Wilcoxon rank-sum test (p<0.05 considered statistically significant). A total of 138 patients were eligible for analysis (see table for clinical data). The median plasma PSA level at time of imaging was 0.34 ng/ml. According to consensus, 61 patients (44 %) had recurrent disease according to consensus while 67 (49 %) had no recurrent disease. Ten (7%) were classified as uncertain. Of the 61 patients with recurrence according to consensus, 2 (3.2 %) were kept under observation, 45 (75%) received sRT in combination with hormone therapy (one only sRT due to age and comorbidities), 9 (15%) hormone therapy and 3 (5%) chemotherapy in combination with hormone therapy. In this group, the median p-PSA level at time of imaging was 0.40 ng/ml. For 20 (33 %) patients, PSMA PET uncovered more advanced disease leading to change of treatment with no corresponding findings in mpMRI. Seven had metastatic disease incompatible with curative treatment which initiated hormone therapy only, in one case with additional chemotherapy. The remaining 13 still received curative treatment, which included dose escalation to affected lymph nodes or RT of single metastatic skeletal lesions (based on PSMA PET). Of the 67 patients with no recurrence according to consensus, 22 (33%) were kept under observation and 45 (67 %) received sRT in combination with hormone treatment. In this group, the median p-PSA level at time of imaging was 0.30 ng/ml, significantly lower than in the group with recurrent disease. In 3 out of 10 patients with findings of uncertain significance according to consensus reading, clinical evaluation resulted in RT dose escalation to possible metastatic lesions based on PSMA PET. Results: