Can 68 Ga-PSMA positron emission tomography and multiparametric MRI guide treatment for biochemical recurrence after radical prostatectomy?

OBJECTIVE: To evaluate the role of multiparametric magnetic resonance imaging (mpMRI) and Gallium-68 (68 Ga)-prostate-specific membrane antigen (PSMA) positron emission tomography (PET)/computed tomography (CT) in guiding salvage therapy for patients with biochemical recurrence (BCR) post-radical prostatectomy. PATIENTS AND METHODS: Patients were evaluated with paired mpMRI and 68 Ga-PSMA PET/CT scans for BCR (prostate-specific antigen [PSA] >0.2 ng/mL). Patient, tumour, PSA and imaging characteristics were analysed with descriptive statistics. RESULTS: A total of 117 patients underwent paired scans to investigate BCR, of whom 53.0% (62/117) had detectable lesions on initial scans and 47.0% (55/117) did not. Of those without detectable lesions, 8/55 patients proceeded to immediate salvage radiotherapy (sRT) and 47/55 were observed. Of patients with negative imaging who were initially observed, 46.8% (22/47) did not reach threshold for repeat imaging, while 53.2% were rescanned due to rising PSA levels. Of these rescanned patients, 31.9% (15/47) were spared sRT due to proven distant disease, or due to absence of disease on repeat imaging. Of the original 117 patients, 53 (45.3%) were spared early sRT due to absence of disease on imaging or presence of distant disease, while those undergoing delayed sRT still maintained good PSA responses. Of note, patients with high-risk features who underwent sRT despite negative imaging demonstrated satisfactory PSA responses to sRT. Study limitations include the observational design and absence of cause-specific or overall survival data. CONCLUSION: Our findings support the use of mpMRI and 68 Ga-PSMA PET/CT in guiding timing and necessity of salvage therapy tailored to detected lesions, with potential to reduce unnecessary sRT-related morbidity. Larger or randomized trials are warranted to validate this.