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SBRT appears effective for patients with low-, intermediate-risk prostate cancer
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Patients with low- and intermediate-risk prostate cancer who underwent stereotactic body radiotherapy demonstrated RFS rates comparable to those of patients who underwent other definitive treatments, according to results of a pooled analysis.
The study included data on 1,100 patients with clinically localized prostate cancer enrolled in separate prospective, phase 2 trials of stereotactic body radiotherapy (SBRT) at eight institutions between 2003 and 2011.
Researchers grouped patients according to risk: 58% were low risk, 30% were intermediate risk and 11% were high risk.
Patients underwent a median dose of 36.25 Gy in four to five fractions. Fourteen percent of patients underwent a short course of androgen deprivation therapy (ADT).
Median follow-up was 36 months.
Forty-nine patients (4.5%) demonstrated PSA failure; of them, nine were later determined to have benign PSA bounces. Researchers observed a PSA bounce >0.2 ng/ml in 16% of patients.
Researchers reported a 5-year biochemical RFS rate of 93% for the entire cohort. Five-year biochemical RFS rates were 95% among low-risk patients, 84% among intermediate-risk patients and 81% for high-risk patients (P<.001).
Among the 135 patients who underwent a minimum 5 years of follow-up, biochemical RFS rates were 99% for low-risk patients and 93% for intermediate-risk patients.
Researchers observed no differences in biochemical RFS based on total SBRT dose (P=.17) or the use of ADT (P=.71).
“The current evidence supports consideration of stereotactic body radiotherapy among the definitive therapeutic options for localized prostate cancer with low and intermediate risk,” the researchers wrote. “The data for high-risk patients is very encouraging but requires longer follow-up at this time. The added benefit of androgen deprivation therapy or any risk group has not yet been demonstrated.”
Disclosure: The researchers report no relevant financial disclosures.
Perspective
Back to TopKevin Stephans, MD
Stereotactic radiation (SBRT) has demonstrated significant advantages compared with conventional radiation in the treatment of both stage I non–small cell lung cancer and select liver malignancies. Similar treatment strategies have been investigated for prostate cancer during the past decade. This series represents by far the largest outcomes analysis reported to date, combining 1,100 patients treated on separate institutional phase 2 protocols at eight centers in the United States and Italy.The reported outcomes are encouraging, with 5-year biochemical RFS rates of 95% for low-risk patients, 84% for intermediate-risk patients and 81% for high-risk patients. The inclusion of 125 high-risk patients is relevant, as nearly all previously published data included predominately low- and intermediate-risk patients.
Treatment was well tolerated, with urinary, bowel and sexual function outcomes approximating conventionally fractionated external beam radiation in a subset of 864 patients (including 194 with 5-year data) who completed Expanded Prostate Cancer Index Composite (EPIC) questionnaires (King CR. Int J Radiat Oncol Biol Phys. 2013;Published online ahead of print Oct. 10).
The findings that further dose escalation and the addition of androgen deprivation therapy (ADT) did not improve biochemical outcomes in this SBRT-treated group are thought-provoking, though potentially limited by the nature of a retrospective review. The range of doses examined (35 Gy to 40 Gy) is relatively narrow, and differences in prescription techniques for SBRT — which may vary by center, or even by patient — can significantly affect biological equivalent dose even for a consistent prescription dose. Likewise, institutional practices, varying follow-up and small advanced-risk patient numbers make assessment of the effect of ADT challenging. The large body of evidence demonstrating a survival advantage for the addition of ADT to conventionally fractionated radiation — albeit only to 70 Gy — should still be weighed when treating more advanced-risk patients with SBRT.
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