NEW YORK (Reuters Health) - Men with organ-confined prostate cancer can be treated with focused stereotactic body radiotherapy (SBRT) as outpatients in as little as five days, saving them time and money, researchers said in Boston Tuesday at the American Society for Radiation Oncology 54th Annual Meeting.
Stereotactic body radiotherapy is highly focused and highly accurate radiotherapy using a few very large doses, explained lead study author Dr. Alan Katz, a radiation oncologist at Flushing Radiation Oncology in Flushing, NY.
"I started treating prostate cancer patients with this technique in 2006, prompted by the success of high-dose rate brachytherapy, which uses high doses delivered through needles implanted into the prostate," Dr. Katz told Reuters Health.
"The thought was to emulate the success of that treatment as a noninvasive, outpatient procedure in five days. The take home message is that prostate cancer has a sensitivity to dose per fraction, meaning that a few high doses have a greater biological effect on prostate cancer than the standard 40 to 45 days of small, daily doses, called IMRT," or intensity-modulated radiation therapy, Dr. Katz said. "This led to higher control rates for cancer than that seen with the standard 40 days of treatment."
For his presentation this week, Dr. Katz pooled his data on the more than 500 men with localized adenocarcinoma of the prostate he's personally treated using SBRT, with data on another 500 patients treated in a similar fashion at seven other institutions.
Those centers included Cyberknife Center of Tampa Bay, Tampa, Florida; Beth Israel Deaconess Medical Center, Boston; Cyberknife Centers of San Diego; San Bortolo Hospital, Vicenza, Italy; Swedish Medical Center, Seattle, WA; Georgetown University Hospital, Washington, DC, and UCLA Medical Center, Los Angeles.
The study included 1,101 patients who were treated with Cyberknife SBRT at a median dose of 36.25 Gy (range 35-40 Gy) delivered either with four or five fractions between 2003 and 2011.
"This is equivalent to a range of 90 to 112 Gy in conventional fractionation," Dr. Katz noted.
Ninety-two percent of the patients were stage T1-2a, and 8% were T2b-3; 72% were Gleason score 6, 20% were Gleason 7, and 8% were Gleason 8-10.
Patients' risk designations according to National Comprehensive Cancer Network (NCCN) criteria were 59% low, 30% intermediate, and 11% high risk. At baseline, the median PSA was 5.4 ng/ml and 88% of PSAs were less than 10 ng/ml; 10% were 10-20 ng/ml, and 2% were above 20 ng/ml.
After a median follow-up of 36 months (range 1 to 66 months), the biochemical relapse-free survival (bRFS) rate for all patients was 93%.
Actuarial five-year bRFS was 95% with a Gleason score of 6 or less, 83% with a Gleason score of 7, and 78% with a Gleason score of 8 or greater, Dr. Katz reported.
When the data were analyzed according to NCCN risk category, the five-year actuarial bRFS rate was 95% for low-risk patients, 90% for intermediate-risk patients, and 80% for high-risk patients, he said.
"Our median PSA is 0.1 at 5 years. These findings are better than those reported for IMRT," Dr. Katz said. "Although we did not report on toxicity in this study, my patients experienced mild toxicity, at least as good as with IMRT."
"Doctors should now be aware of this treatment and advise their patients of its high success rate and low toxicity, all in five days," Dr. Katz said. "I hope that our pioneering efforts will lead to much greater awareness and acceptance of this technique. Not only do patents save time and money traveling for their treatments, but the savings to Medicare and insurance companies are potentially enormous. The cost of this treatment is less than half the cost of the IMRT."
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