BOSTON —Patients with organ-confined prostate cancer (PCa) may have a new treatment option using high doses of focused stereotactic body radiotherapy (SBRT) instead of traditional lengthy radiotherapy courses or surgery, according to new data presented at the American Society for Radiation Oncology annual meeting.

“Therapy options for patients with organ-confined prostate cancer can be time consuming and costly with traditional radiotherapy methods,” said lead researcher Alan Katz, MD, JD, a radiation oncologist at Flushing Radiation Oncology in Flushing, N.Y. “We found that higher doses of stereotactic radiotherapy with fewer fractions yielded great results in terms of tumor control. Our results show that additional standard radiation treatment added to SBRT is probably unnecessary, even with high-risk patients.”

Dr. Katz, who presented the study findings, said this is the first long-term study of prostate SBRT with a large number of patients. The study evaluated the biochemical relapse-free survival (bRFS) rates over a five-year period for patients with organ-confined PCa. Of the 1,101 patients in the study, 92% had clinical stage T1-2a and 8% had stage T2b-3 cancer. In addition, 72% had Gleason 6, 20% had Gleason 7, and 8% had Gleason 8-10 disease. Low-, intermediate-, and high-risk patients made up 59%, 30%, and 11% of the study population, respectively.

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The study showed that prostate tumors appear to be very sensitive to a higher, targeted dose of radiation rather than more frequent lower doses over time, which means that patients now have a viable option of choosing a one-week course of therapy as opposed to an eight-week or nine-week course of treatment.

The study evaluated low-, intermediate-, and high-risk patients. At five years, their actuarial disease-free survival rates were 95%, 90%, and 80%, respectively. The median dose was 36.25 Gy (range 35-40 Gy) delivered in four or five fractions. This was equivalent to a range of 90-112 Gy in conventional fractionation.

The five-year actuarial biochemical relapse-free survival rate for patients with a Gleason score of 6 or less was 95%. It was 83% and 78% for those with a Gleason score of 7 and 8-10, respectively. The actuarial five-year bRFS rates for low- and intermediate-risk cases were 97% and 89%, respectively.

For low- and intermediate-risk cases, these results compared favorably with other modalities at five years. High-risk cases also appeared to do well, although the results for this subset of patients are preliminary due to the small number of patients with five-year follow-up. The median follow-up for all cases was 36 months. Biochemical relapse, defined as a rise greater than 2 ng/mL above nadir, was determined for 49 patients, nine of whom had a resolution of the rise and showed no clinical signs of a relapse. Additionally, androgen deprivation therapy (ADT) was given to 146 patients and appeared to make no difference in biochemical relapse risk.

“With these high doses, you probably don’t need ADT,” Dr. Katz told Renal & Urology News.  “We found it is very safe. We aren’t losing anything in terms of the side effect profile.  Basically, you see about 5%-10% of patients experiencing some late urinary irritation, urgency, frequency and burning.”