CHICAGO—Hypofractionated stereotactic body radiotherapy (SBRT) delivered by the CyberKnife can result in minimal toxicity, good short-term PSA response, and preservation of erectile function in most men with localized prostate cancer, according to new data presented here at the American Society for Radiation Oncology’s annual meeting.

“With a median follow-up of 24 months, we found that the toxicity profile using this type of radiation was very good in men with early stage disease,” said investigator Debra Freeman, MD, a radiation oncologist from Naples, Fla.

“The dose of radiation per day is significantly more with SBRT than with traditional radiation. Traditional radiation is usually given over eight or nine weeks. [SBRT] gives an equivalent amount of radiation in five days but is much more targeted. We were very pleased to see the toxicity was extremely low—lower than what we see acutely with traditional radiation because less normal structures near the prostate have been exposed to treatment.”  

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Dr. Freeman presented results from a cohort of 113 patients treated with SBRT for early stage prostate cancer between February 2005 and December 2006. Subjects had localized, biopsy-proven prostate cancer (clinical stage T1cN0M0 to T2cN0M0). Of the 113 men, 81 had a Gleason score of 6. The mean initial PSA was 6.0 and initial prostate volume ranged from 15.5 to 109 mL. Twenty-two men received neoadjuvant hormonal therapy. 

Image-guided targeting and tracking was performed with implanted gold fiducials. Dr. Freeman’s group used CT and magnetic resonance imaging (MRI) scans to accurately identify the prostate gland. The planning target volume included the gross tumor volume with a 5 mm margin anteriorly and laterally and a 3 mm margin posteriorly. Most men received 35 Gy of radiation, which was administered in five fractions.

At a median follow-up of 24 months, the mean PSA value was 0.78 ng/mL and only two patients had developed biopsy-proven local relapse. Distant metastases developed in one patient. Acute adverse effects were generally mild and resolved shortly after treatment. A single Grade 3 rectal complication (bleeding) was reported. In addition, 82% of the patients who were sexually potent before treatment were able to maintain erectile function post-treatment.

“As we follow these patients long-term, we are finding very little toxicity compared to some traditional forms of radiation,” Dr. Freeman told Renal & Urology News. “When we look at PSA levels, they are going low and staying low. We know this is a predictor of long-term disease control. We have to have five-year data, seven-year data, and 10-year data to really be able to state that we have long-term control, but the trend in the PSA is certainly very promising in that regard.”

Dr. Freeman called SBRT “another tool in the armamentarium” for early stage prostate cancer. “For urologists who are not familiar with SBRT, I think they would find that patients are happier with the therapy, and there are fewer patients coming back to their offices complaining of problems due to radiation.”