Stereotactic Radiotherapy to Oligoprogressive Lesions Detected With 68Ga-PSMA-PET/CT in Castration-Resistant Prostate Cancer Patients.

Purpose/objective(s) Few studies have investigated the feasibility of MDT in metastatic castration-resistant prostate cancer (CRPC) patients with heterogeneous patient populations with different treatment strategies and various imaging modalities other than gallium prostate-specific membrane antigen-positron emission tomography (68Ga-PSMA-PET/CT) for detecting oligoprogressive lesions. We assessed the outcomes of stereotactic body radiotherapy (SBRT) to treat oligoprogressive castration-resistant prostate cancer (CRPC) patients with ≤5 lesions using 68Ga-PSMA-PET/CT. Materials/methods The clinical data of 67 CRPC patients with 133 lesions treated with 68Ga-PSMA-PET/CT-based SBRT were retrospectively analyzed. All of the patients had oligoprogressive disease during androgen-deprivation therapy (ADT). The inclusion criteria were as follows: a histologic diagnosis of PC on primary tumor biopsy, less than or equal to 5 bone and/or lymph node metastases detected with 68Ga-PSMA-PET/CT during ADT, being castration-resistant according to the European Association of Urology guidelines, a controlled primary tumor, SBRT fraction doses of at least 6 Gy per fraction and a biologically effective dose (BED) of at least 90 Gy using α⁄β of 3 Gy. The prognostic factors for overall- (OS) and progression-free survival (PFS) and the predictive factors for switching to next-line systemic treatment (NEST) and NEST-free survival (NEST-FS) were analyzed. Results With a median follow-up of 17.5 months, the 2-year overall survival (OS) and PFS rates were 86.9% and 34.4%, respectively. Most of the patients had GS 9 or 10 tumors and locally advanced disease. The most frequent oligoprogressive site was bone only (64.2%), and more than half of the patients (53.7%) had a single metastasis. The median number of metastases was 1 (range, 1-5). In the case of bone metastasis, the most adopted methods were single-dose 16 Gy and 18 Gy, and the most adopted prescription for nodal metastasis was 30-35 Gy delivered in 5 fractions. The PSA response after SBRT was observed in 49 patients (73.1%). Progression was observed in 37 patients (55.2%) at a median of 11.0 months following SBRT. Forty-five patients (67.2%) remained on ADT after SBRT, and 22 patients (32.8%) had a NEST change at a median of 16.4 months after MDT. Patients with a NEST change had higher post-SBRT PSA values and fewer PSA nadirs after MDT than their counterparts. In multivariate analysis, higher pre-SBRT PSA values were the only significant predictor for worse OS and NEST-FS, and no significant factor was found for PFS. No serious acute or late toxicities were observed. Conclusion This study demonstrated the feasibility of MDT using SBRT to treat oligoprogressive lesions by 68Ga-PSMA-PET/CT in CRPC patients is efficient and well-tolerated, prolonging the effectiveness of ADT by delaying NEST.