Single-fraction stereotactic body radiotherapy promising for local prostate cancer recurrence

Researchers from Germany found that even in intensively pretreated prostate cancer patients single-fraction, PSMA-PET- and mpMRI-guided focal stereotactic body radiotherapy was found to be safe, efficient, and timesaving. The study results were published in the journal BJU International.  

Prostate cancer (PCa) is the most frequent malignant tumor in adult men. There are various combinations of therapies like radical prostatectomy, external beam radiotherapy, or a combination of both. New therapeutic advances have developed with the use of stereotactic body radiotherapy (SBRT). But to date evidence has been limited to the use of fractionated stereotactic body radiotherapy (SBRT) with not much data on single-fraction SBRT in conjunction with prostate-specific membrane antigen positron emission tomography (PSMA-PET) and multiparametric magnetic resonance imaging (mpMRI) guidance. Hence researchers from Germany conducted a study to analyze the efficacy and safety of focal PSMA-PET and mpMRI-guided single-fraction stereotactic body radiotherapy (SBRT) for the treatment of PCa local recurrences.  

Patients with PSMA-PET-positive PCa local recurrences treated with single-fraction SBRT between 2016 and 2020 were included. Subsequent recurrences or metastatic spread were identified based on increasing prostate-specific antigen (PSA) levels and PSMA-PET imaging was used for the evaluation. 

Results: 

• A total of 64 patients were identified.
• Patients received various treatments before SBRT 31 patients were treated with radical prostatectomy [RP], 18 with external beam radiotherapy [EBRT] with RP, five with EBRT, and the remaining 10 were given other combinations.
• The median follow-up was 21.6 months.
• The median PSA level before SBRT was 1.47 ng/mL.
• A single-fraction treatment with a median prescription dose and isodose line of 21 Gy and 65%, were given to all patients respectively. 
• At the time of SBRT, six patients (9%) received androgen deprivation therapy (ADT).
• PSA levels decreased after SBRT (P = 0.03) and three local recurrences were detected during the follow-up.
• The progression-free survival after 1-, 2-, and 3 years was 85.3%, 65.9%, and 51.2%, respectively.
• Six patients (9%) started ADT after SBRT due to disease progression.
• The rates of newly started ADT after 1-, 2-, and 3 years were 1.8%, 7.3%, and 22.7%, respectively. Grade 1 or 2 toxicities occurred in six patients (9%); no high-grade toxicity was observed. 

Thus, this first analysis of single-fraction, PSMA-PET- and mpMRI-guided focal SBRT has shown promising results. The use of ADT could be delayed with recurrence-directed treatments and could avoid prostate bed irradiation in selected patients. 

Take-home points: 

• Stereotactic body radiotherapy (SBRT) is an emerging technology that has become increasingly used to treat localized prostate cancer. This study was the first to evaluate prostate-specific membrane antigen PET– or multiparametric MRI–guided single-fraction SBRT in patients with prostate cancer recurrence. There were 64 patients identified, with the majority having previously undergone radical prostatectomy. There were significant reductions in prostate-specific antigen (PSA) levels after SBRT. The progression-free survival rate at 3 years was 51.2%. There were no instances of high-grade toxicity.
• This study of single-fraction SBRT for local prostate cancer recurrence found that the treatment was well-tolerated and resulted in a significant reduction in PSA levels that appeared durable. 

Further reading: Ehret F, Hofmann T, Fürweger C, et al. Single-fraction prostate-specific membrane antigen positron emission tomography- and multiparametric magnetic resonance imaging-guided stereotactic body radiotherapy for prostate cancer local recurrences [published online ahead of print, 2022 Sep 17]. BJU Int. 2022;10.1111/bju.15894. doi:10.1111/bju.15894