High-dose stereotactic body radiotherapy (SBRT) for men with newly-diagnosed low- or intermediate-risk prostate cancer results in shorter treatment times, low severe toxicity, and excellent cancer control rates, according to research presented at the 58th Annual Meeting of the American Society for Radiation Oncology (ASTRO) in Boston, MA (Sept 25-26).
While prostate tumors generally respond well to radiation therapy, patients often experience a number of adverse events associated with treatment, including damage to healthy, non-cancerous tissue in the genitourinary and gastrointestinal systems. SBRT is a technique that more precisely targets diseased tissue with high doses of radiation therapy in a smaller number of fractions. This method helps to spare surrounding tissue thereby reducing toxicity to non-cancerous cells and the severity of adverse events patients experience. SBRT has become the standard of care for patients with lung cancer unable to undergo surgery,
In the first large, multi-institutional study of SBRT in prostate cancer with long-term follow-up, researchers led by Robert Meier, MD, Swedish Medical Center (Seattle, WA), analyzed the effect of SBRT in 309 men with newly diagnosed prostate cancer. All of the men received SBRT via a non-isocentric robotic platform, with radiation therapy dose to the prostate of 40 Gy administered in five treatment sessions of 8 Gy each. Intermediate risk patients received a dose of 36.25 Gy to the seminal vesicles. Concurrent and adjuvant androgen ablation therapy were prohibited among study participants.
Researchers also used the National Cancer Institute’s Common Terminology Criteria for Adverse Events (CTCAE) version 3.0 to measure the toxicity of treatment and the ASTRO-consensus and the nadir+2 definitions to assess biochemical failure. Overall survival was evaluated as a secondary outcome.
At five years following SBRT, researchers found that 97% of patients were free from prostate cancer progression. Those with low-risk disease also performed significantly better than traditional norms, with a 5-year relapse-free survival rate (RFS) of 97.3% versus the 93% historical disease-free survival control rate. Additionally, overall survival was 95.6% for the entire cohort.
Further, only 2% of patients experienced serious adverse events in the five years following SBRT and only 5 grade 3 genitourinary adverse events were reported in the entire cohort. No grade 4 or 5 toxicities were reported, nor any grade 3 gastrointestinal adverse events. However, about half of patients experienced grade 1 gastrointestinal and/or genitourinary adverse events.
“Our results illustrate how advanced technology has radically improved our ability to target cancer,” said Dr Meier. “After following patients for more than five years, we found that serious side effects from a brief course of SBRT were uncommon and that cancer control rates were very favorable compared to historical data,” authors of the study concluded. “Our trial confirms that SBRT may be preferable to other treatment approaches for newly-diagnosed cases of prostate cancer, including more aggressive disease.”
