Ultra-high single-dose radiotherapy effective for intermediate-risk prostate cancer

Ultra-high single-dose radiotherapy (SDRT) demonstrated comparable efficacy and safety as curative hypofractionated stereotactic body radiotherapy (SBRT) in patients with organ-confined prostate cancer, according to study findings published in JAMA Oncology.¹

Data from the randomized, phase 2 PROSINT clinical trial (NCT02570919) presents an opportunity to further evaluate indications for SDRT as an alternative treatment option for patients with intermediate-risk prostate cancer, according to the researchers.

“This proof-of-concept parallel-group randomized clinical trial confirms that 24 Gy SDRT is feasible and safe in the treatment of organ-confined prostate cancer,” wrote the investigators. “The 5 × 9 Gy SBRT prostate immobilization and high-precision technique had been previously proven feasible and safe.”

The study population included 30 men with intermediate-risk prostate cancer randomized to either the SBRT or SDRT treatment arms. The median ages for each arm were 66.3 years and 73.6 years for the SBRT arm and SDRT arm, respectively.

The primary end point of the trial was toxic effects, with key secondary end points focusing on prostate-specific antigen (PSA) responses and quality of life. Patient-reported quality of life was measured using the International Prostate Symptom Score (IPSS) and Expanded Prostate Cancer Index Composite (EPIC)–26 questionnaires.

Data on the toxic effects found that grade 1 (HR, 0.41; 90% CI, 0.13-1.27) and grade 2 or greater (HR, 1.07; 90% CI, 0.21-5.57) cumulative late actuarial urinary toxic effects were similar. More, comparable data was observed for actuarial grade 1 late gastrointestinal (GI) toxic effects (HR, 0.37; 90% CI, 0.07-1.94), while no grade 2 or greater late GI toxic effects were observed.

For both arms, the PSA levels declined to under 0.5 ng/mL by the 36-month point. In the favorable intermediate-risk disease population, there were no PSA relapses observed, while the actuarial 4-year PSA relapse-free survival for the unfavorable disease population was 75.0% in the SBRT arm and 64.0% in the SDRT arm (HR, 0.76; 90% CI, 0.17-3.31).

The EPIC-26 quality-of-life analysis for both arms found that the median score for the genitourinary and GI domains dropped at the 1-month point, followed by a return to pre-treatment scores at the 3-month observation. For the IPSS analysis, 20% of patients receiving SDRT (90% CI, 3%-37%) had late urinary flare symptoms occur at 9 to 18 months.

“This study offers encouraging perspectives on the feasibility and safety of 24 Gy SDRT in organ-confined prostate cancer,” wrote the investigators. “Despite the limitation of a small sample size, the SDRT PSA end points recapitulate the outcomes of curative extreme hypofractionated 5 × 9 Gy SBRT reported here and in the recent literature.”

The main limitations of the phase 2 trial include the single-institution design, the small sample size of 30 patients, and the median follow-up limited to only 48 months.

Due to the data found from this phase 2 clinical trial, the investigative team suggests further studies to evaluate SDRT as a cost-effective and safe treatment option for this cohort of patients with prostate cancer.

“SDRT provides advantages in patient convenience as a result of the reduced number of visits,” wrote the investigators. “This could potentially lead to same-day planning and treatment, as well as provide significant cost savings, an issue already addressed relative to SBRT schemes, a major consideration in today’s increasingly cost-conscious environment.”

Reference

1. Greco C, Pares O, Pimentel N, et al. Safety and Efficacy of Virtual Prostatectomy With Single-Dose Radiotherapy in Patients With Intermediate-Risk Prostate Cancer. JAMA Oncol. March 11, 2021. doi:10.1001/jamaoncol.2021.0039