Long-Term Evidence Supports Use of SBRT in Prostate Cancer

Amar U. Kishan, MD

Amar U. Kishan, MD

Stereotactic body radiation therapy (SBRT) has been found to be a safe and effective option for patients with low- and intermediate-risk prostate cancer, according to long-term outcome data recently published in JAMA Network Open.¹

Most of this patient population will undergo conventional radiation therapy, which requires them to visit a facility for treatment daily, for an average duration of 9 weeks, said lead study author Amar U. Kishan, MD, in a press release.² With SBRT, however, patients can reduce their treatment course to approximately 4 or 5 days.

“With the improvements being made to modern technology, we’ve found that using stereotactic body radiotherapy, which has a higher dose of radiation, can safely and effectively be done in a much shorter timeframe without the additional toxicity or compromising any chance of a cure,” said Kishan, an assistant professor of radiation oncology at the David Geffen School of Medicine at University of California at Los Angeles (UCLA) and researcher at the UCLA Jonsson Comprehensive Cancer Center.

Although this form of external beam radiation therapy has been in use for almost 2 decades, the treatment modality has not been widely accepted, as safety and efficacy data regarding its use in the long-term has been sparse.

To evaluate the long-term outcomes of patients with prostate cancer who received SBRT, Kishan and his UCLA team launched a cohort study, which analyzed data from 2142 men who were enrolled in 10 single-institution phase II trials and 2 multicenter phase II trials.

Patients had received treatment with SBRT between January 1, 2000 and December 31, 2012. Doses of the therapy ranged from 33.5 Gy to 40.0 Gy in 4 to 5 fractions, with 88% (n = 1885) of patients having received 5 fractions. Therapy was delivered either on consecutive days, every other day, or once a week, according to individual protocol specifications.

Of the 2142 men who were determined eligible for analysis, 55.3% (n = 1185) had low-risk disease, 32.3% (n = 692) had favorable intermediate-risk disease, and 12.4% (265) had unfavorable intermediate-risk disease.

The primary disease control endpoint for the study was the cumulative incidence of recurrence, which was determined using the Phoenix definition of a prostate-specific antigen level of 2 ng/mL or more, higher than the lowest post-radiation value.

The median follow-up period for these patients was 6.9 years (interquartile range, 4.9-8.1 years). Investigators estimated the cumulative incidence of recurrence using a competing risk framework. Results showed that the 7-year cumulative biochemical recurrence rate for men with low-risk disease was 4.5% (95% CI, 3.2%-5.8%), 8.6% (95% CI, 6.2%-11.0%) for favorable intermediate-risk disease, and 14.9% (95% CI, 9.5%-20.2%) for those with unfavorable intermediate-risk disease. The biochemical recurrence rate for all patients with intermediate-risk disease was 10.2% (95% CI, 8.0%-12.5%).

For each individual study, physician-scored gastrointestinal (GI)- and genitourinary (GU)-related adverse event (AE) outcomes were defined. Acute toxic events were defined as an adverse event occurring within the first 90 days after completion of SBRT. The analysis did not reveal any evidence to suggest that the therapy caused worse toxicities in the long-term.

Specifically, results showed that the crude incidence of acute grade 3 or higher GI-related AEs was 0.09% (n = 2), while incidence of acute grade ≥3 GU-related AEs was 0.6% (n = 13). Further, the 7-year cumulative incidence of late grade ≥3 GI-related AEs was 0.4% (95% CI, 0.2%-0.8%) and of late grade ≥3 GU-related AEs was 2.4% (95% CI, 1.8%-3.2%).

“We not only confirm that this method is both safe and effective, but we provide significant evidence that this could be a viable treatment option for men with low- and intermediate-risk prostate cancer,” concluded Kishan.

References

1. Kishan AU, Dang A, Katz AJ, et al. Long-term outcomes of stereotactic body radiotherapy for low-risk and intermediate-risk prostate cancer. JAMA Netw Open. 2019;2(2):e188006. doi: 10.1001/jamanetworkopen.2018.8006.
2. Shorter Course Of Radiation Therapy Effective In Treating Men With Prostate Cancer UCLA. Published February 8, 2019. https://bit.ly/2DyzXd6. Accessed February 12, 2019.