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SBRT appears effective for patients with low-, intermediate-risk prostate cancer
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 TopThe 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.