ASTRO 2016: SBRT Offers Patients With Prostate Cancer High Disease Control and Low Toxicity in Fewer Treatments
High-dose stereotactic body radiotherapy (SBRT) for men newly-diagnosed with low- or intermediate-risk prostate cancer results in shorter treatment times, low severe toxicity, and excellent cancer control rates, according to research presented by Meier et al at the 58th Annual Meeting of the American Society for Radiation Oncology (ASTRO). The study is the first large, multi-institutional study of SBRT in prostate cancer with long-term follow-up.
Although prostate tumors generally respond well to radiation therapy, the possibility of radiation exposure to healthy tissue in the genitourinary and gastrointestinal systems can be of concern. SBRT is an advanced technique that precisely targets high doses of radiotherapy to the tumor in a small number of fractions, simultaneously avoiding surrounding tissue and reducing toxicity to noncancerous cells. The technique has become the standard of care for many nonsurgical lung cancer patients, as it limits exposure to the heart and surrounding lungs. When treating tumors in the prostate, SBRT avoids the adjacent bladder, sex organs, and rectum.
“Single-institution studies on the use of SBRT as the primary treatment for prostate cancer have illuminated the treatment as a cost-effective and faster alternative to IMRT,” said Robert Meier, MD, lead author of the study and a radiation oncologist at Swedish Medical Center in Seattle. “Our study is the first to contribute multicenter data that support the use of SBRT as front-line therapy for men with prostate cancer.”
Study Details
A total of 309 men with newly diagnosed prostate cancer were enrolled in the trial at 21 community, regional, and academic hospitals across the U.S. Eligible patients had either low-risk disease (CS T1–T2a, Gleason 6, PSA < 10) (n = 172) or intermediate-risk disease (CS T1c–T2b with either Gleason 7 and PSA < 10, or Gleason 6 and PSA 10–20). All of the men received SBRT via a nonisocentric robotic platform, with a radiotherapy 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.
Primary outcomes included genitourinary and gastrointestinal toxicities and relapse-free survival. Researchers measured toxicity using the National Cancer Institute’s Common Terminology Criteria for Adverse Events (CTCAE) version 3.0. Biochemical failure was assessed using the ASTRO-consensus and the nadir+2 definitions. Overall survival was measured as a secondary outcome for the study. Actuarial overall survival and relapse-free survival were calculated with the Kaplan-Meier statistical method. Median follow-up was 61 months.
Findings
At 5 years following SBRT, 97% of patients were free from prostate cancer progression. In low-risk patients, the cancer control rates was superior to historical controls. Specifically, in the low-risk group, the 5-year relapse-free survival rate was 97.3%, which is superior to the 93% historical comparison disease-free survival control rate (P = .014). Actuarial 5-year overall survival was 95.6% for the entire cohort. Actuarial 5-year nadir+2 relapse-free survival was 97.1% for all patients, representing 97.3% of low-risk and 97.1% of intermediate-risk patients. Actuarial 5-year ASTRO relapse-free survival was 92.3% and 91.3% for low- and intermediate-risk groups, respectively.
Fewer than 2% of all patients experienced serious side effects in the 5 years following SBRT. Five grade 3 genitourinary side effects were reported in four of the 309 study participants. There were no reported grade 4 or 5 toxicities, nor any grade 3 gastrointestinal toxicities. Between half and two-thirds of patients experienced less serious side effects, with rates of 53 and 59% for grade 1 genitourinary and gastrointestinal toxicities, respectively, and rates of 35 and 10% for grade 2 genitourinary and gastrointestinal toxicities, respectively. These side effects were usually temporary.
“Our results illustrate how advanced technology has radically improved our ability to target cancer,” said Dr. Meier. “After following patients for more than 5 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. Our trial confirms that SBRT may be preferable to other treatment approaches for newly-diagnosed cases of prostate cancer, including more aggressive disease.”
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
