Of the 2,142 patients evaluated, slightly more than half (55.3 percent, n=1,185) had low-risk disease; about a third (32.3 percent, n=692) had favorable intermediate-risk disease; and 12.4 percent (n=265) had unfavorable intermediate risk disease, that is, they had multiple intermediate risk factors, primary Gleason pattern 4 disease or ≥50 percent positive cores. Median patient age was 67.9 years (range: 41-92).

Most patients were treated daily (47.3 percent) or every other day (47.4 percent), while a small percentage (5.3 percent) were treated once a week. Doses ranged from 33.5 to 40 Gray (Gy) and were given in four or five fractions (88 percent of patients received five fractions). A small percentage (5.4 percent, n=115) of patients received concurrent androgen deprivation therapy (ADT, also known as hormone therapy), with utilization rates ranging from 3.6 percent in low-risk patients to 9.4 percent in unfavorable intermediate-risk patients. The median duration of ADT was three months.


Patients were followed for a median period of 6.9 years (interquartile range (IQR): 4.9-8.1). Those who were low-risk were followed for 7.1 years (IQR 5.4-8.8); those with favorable intermediate-risk were followed for 6.2 years (IQR 4.1-7.9); and those in the unfavorable intermediate-risk group were followed for 5.9 years (IQR 3.3-7.1). A subset of 305 patients had a minimum follow-up of nine years, and a median follow-up of 9.8 years. These included 223 patients with low-risk disease, 65 patients with favorable intermediate-risk disease and 27 patients with unfavorable intermediate-risk disease.

Researchers measured the safety and efficacy of stereotactic radiation using the following criteria: a cumulative incidence of biochemical recurrence (BCR) marked by rising PSA levels following SBRT; cumulative incidence of distant metastases (DM), i.e., the cancer spreading from the tumor to distant organs or lymph nodes; biochemical recurrence-free survival (BCRFS); and overall survival. They also evaluated the occurrence short-term adverse events within 90 days following completion of SBRT.

None of the patients in the study died from prostate cancer. In all, 100 patients (6 percent) experienced recurrence and 10 experienced distant metastases (0.6 percent). In the low-risk group, 95.5 percent of patients were free from BCR at seven years. In the favorable intermediate-risk group, 91.4 percent of patients were BCR-free at seven years. In the unfavorable intermediate-risk group, 85.1 percent were BCR-free at seven years.

Overall survival rates for the low-risk and favorable intermediate-risk groups were 91.4 and 93.7 percent at seven years following treatment. In the unfavorable intermediate-risk group, the most aggressive form of cancer in this study, overall survival was 86.5 percent at seven years.

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