Post-prostatectomy stereotactic body radiotherapy (SBRT) to the prostate bed, with or without elective nodal irradiation, demonstrates promising tolerability in patients with localized prostate cancer. The prospective trial, presented at the 2024 American Society for Radiation Oncology (ASTRO) annual meeting, explored the use of linac-based ultrahypofractionated radiotherapy in the salvage setting.
The study enrolled 30 patients with undetectable PSA postoperatively, pathologic stage T3 or T4, positive surgical margins, or postoperative detectable PSA. The treatment protocol consisted of SBRT to the prostate bed (30 Gy in 5 fractions, once weekly), with optional SBRT to pelvic lymph nodes (25 Gy in 5 fractions, once weekly) and androgen deprivation therapy (ADT) for 6-24 months. The primary endpoint was acute genitourinary (GU) and gastrointestinal (GI) toxicities, while secondary endpoints included late toxicities and health-related quality of life (HRQoL).
Toxicity and Quality of Life
Researchers reported no grade ≥3 acute GU or GI toxicities. However, four late grade 3 toxicities were observed: urinary incontinence in one patient and erectile dysfunction in three patients. During the acute period, 30% of patients experienced Grade 2 GI toxicities, while only 3.3% had Grade 2 GU toxicity. In terms of HRQoL, 26.7% of patients reported acute moderate/severe Minimally Clinically Important Change (MCIC) in the urinary domain, 53.3% in the bowel domain, and 10.0% in the sexual domain.
Clinical Implications
Dr. Chia-Lin Tseng from Sunnybrook Health Sciences Centre, Toronto, emphasized that post-prostatectomy SBRT to the prostate bed is well-tolerated, with minimal impact on health-related quality of life in the acute period. The median follow-up was 37.7 months, and further follow-up is warranted to better evaluate long-term toxicity, biochemical disease-free survival, and patterns of failure for this treatment modality in the post-prostatectomy space. A multicenter expanded cohort has completed accrual to gain broader experience and more robust safety and efficacy data for this treatment modality.
Background on Hypofractionated Radiotherapy
Salvage radiation therapy (RT) post-prostatectomy at 60-66 Gy in conventional fractionation is a well-accepted practice. Moderately hypofractionated RT (52.5-62.5 Gy in 20-25 fractions) has also been shown to be an acceptable practice standard. Linac-based ultra hypofractionated RT utilizes a linear accelerator to deliver high doses of radiation in fewer fractions than conventional radiotherapy. Data suggest that prostate cancer may be more sensitive to higher doses per fraction of RT, aligning with the Stereotactic Body Radiotherapy (SBRT) paradigm. However, there is limited data on SBRT in the early salvage post-prostatectomy setting, making this study a valuable contribution to the field.
