68Ga-PSMA ligand PET/CT-based radiotherapy in locally recurrent and recurrent oligometastatic prostate cancer

The goal of this work was to evaluate the early efficacy of Ga-68-PSMA ligand PET/CT imaging for radiotherapy of locally recurrent and/or oligometastatic prostate cancer. A total of 29 patients with biochemical recurrence received a Ga-68-PSMA ligand PET/CT for restaging of disease, followed by 3D conformal radiotherapy of metastases or intensity-modulated radiation therapy of the prostate bed. Prostate-specific antigen (PSA) levels and imaging procedures served as the reference standard to assess the treatment efficacy. PET/CT was positive in 96.6% of patients and revealed that 13.8% of patients had locally recurrent disease, 58.6% had isolated lymph node metastases, 20.7% had isolated bone metastases, and 3.4% showed lymph node metastases and a vertebral metastasis. The median follow-up was 8.3 months (range 3.0-17.3 months). The median PSA prior to radiotherapy was 1.47 ng/ml (range 0.52-32.01 ng/ml) and showed a statistically significant decrease to 0.58 ng/ml (range < 0.07 to 6.33 ng/ml, p < 0.001). Two patients (6.8%) developed progressive disease outside the radiation field after 12.0 and 12.7 months, yielding a local control rate of 100% at the median follow-up. No grade III acute toxicity or late toxicity grade II was observed. Only 2 patients (6.8%) reported persisting grade I diarrhoea according to the LENT-SOMA criteria 3 months after radiotherapy. Deterioration of the urinary or faecal continence was not observed. Preliminary results in the presented cohort suggest that radiotherapy based on Ga-68-PSMA ligand PET/CT yields effective local control and significant treatment response in terms of PSA levels in the absence of clinically important side effects. Furthermore, this approach delayed the necessity of androgen deprivation therapy or systemic therapy.