Stereotactic body radiation therapy (SBRT) delivered via the CyberKnife can achieve excellent outcomes with minimal toxicity in patients with prostate cancer. Importantly, this technique delivers therapeutic doses of radiation in four to five fractions, which reduces the number of clinic visits from 8 weeks with standard intensity-modulated radiation therapy (IMRT) to 1 to 2.5 weeks for SBRT. This has huge implications for patient convenience and cost-savings to the health-care system, but experts agree that longer follow-up is needed. These findings of two prospective studies were reported at the 54th American Society for Radiation Oncology (ASTRO) Annual Meeting in Boston.
Stereotactic body radiation therapy refers to ultraprecise delivery of very-high-dose radiation using converging, finely collimated beams (see sidebar, “Two Modes of Precision Radiotherapy”). The CyberKnife system, based on robotic technology, was used to deliver SBRT in both studies. Typically, a course of radiation with CyberKnife SBRT takes five sessions. SBRT technology is currently available at about 150 centers in the United States.
In a pooled analysis of 1,100 patients with organ-confined prostate cancer treated with Cyberknife SBRT, actuarial 5-year biochemical control (undetectable prostate-specific antigen [PSA] level) was 95% for low-risk patients, 90% for intermediate-risk patients, and 80% for high-risk patients, reported Alan J. Katz, MD, Flushing Radiation Oncology, Flushing, New York.1 Results were similar in 150 of these patients who also received androgen-deprivation therapy. Results were also similar with three different dose levels of SBRT (< 35 Gy vs 36–37 Gy vs 38–40 Gy).
For this analysis, Dr. Katz contributed data from 515 consecutive patients, and the other 585 patients were treated at one of seven other centers. Among all patients, 59% were low-risk, 30% were intermediate-risk, and 11% were high-risk.
Median follow-up was 36 months (range, 1–66); 465 of Dr. Katz’ patients had a minimum of 4 years of follow-up. Patients were treated from 2003 to 2010. Median dose was 36.25 Gy delivered in either four or five fractions.
“These results are 5% to 10% better than what is seen with standard IMRT, which takes 40 to 45 days to deliver. At this point, the statistics should encourage men with organ-confined prostate cancer to seek SBRT as an alternative to IMRT, brachytherapy, or prostate surgery,” he stated. Further, the results suggest that there is no need for androgen-deprivation therapy with SBRT, he added.
Regarding toxicity and the need for longer follow-up, Dr. Katz said that he has patients out to 7 years, and experience suggests that patients who develop significant side effects generally develop them within 2 to 3 years. “At 7 years, we see no new toxicities,” he stated.
At a press conference, Dr. Katz said, “SBRT represents huge savings in time for patients with prostate cancer and in costs to payers. Medicare reimbursement for SBRT is a median of $22,000 vs $40,000 to $45,000 per patient, making SBRT 50% less costly than standard IMRT treatment.”
A second report focused on 129 patients with intermediate-risk, organ-confined prostate cancer treated at 21 different institutions from December 2007 to April 2010.2 Median follow-up of patients in this prospective phase II study was 3 years (range, 2.5–4 years).
Urinary side effects in men treated with stereotactic body radiation therapy, as assessed by the Expanded Prostate Cancer Index Composite (EPIC), were evident early in the course of treatment, but by 6 months later, returned to baseline values, said Robert Meier, MD, Swedish Radiosurgery Center, Seattle, who gave this presentation. A similar pattern was seen in EPIC quality-of-life scores for bowel side effects, which were seen early in the course of treatment, began to improve by 6 months, and reached baseline values by 2 years. Most urinary and bowel side effects were grade 1 or 2, Dr. Meier said.
Biochemical control was excellent (99.2%), with only 1 of 129 patients who had a 2 ng/mL rise in PSA after the current nadir.
“These results are extraordinarily good. We typically see 10% to 20% biochemical failure at 4 years with IMRT and proton-beam therapy,” Dr. Meier stated. ■
Disclosure:Drs. Meier and Katz reported no potential conflicts of interest.
1. Katz A, Freeman D, Aronovitz, J, et al: Five-year biochemical control rates for stereotactic body radiotherapy for organ confined prostate cancer: A multi-institutional pooled analysis. 54th ASTRO Annual Meeting. Abstract 365. Presented October 31, 2012.
2. Meier R, Kaplan I, Beckman A, et al: Stereotactic body radiation therapy for intermediate-risk organ-confined prostate cancer: Interim toxicity and quality of life outcomes from a multi-institutional study. 54th ASTRO Annual Meeting. Abstract 366. Presented October 31, 2012.