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Stereotactic body radiation therapy for prostate cancer: Is the technology ready to be the standard of care?

  
  
  
  
  
Cancer Treatment Reviews, 12/06/2012

Zaorsky NG et al. – Prostate cancer is the second most prevalent solid tumor diagnosed in men in the United States and Western Europe. Stereotactic body radiation therapy (SBRT) is touted as a superior type of external beam radiation therapy (EBRT) for the treatment of various tumors. The authors review the impetus behind SBRT and the current clinical evidence supporting its use for prostate cancer, thus providing oncologists and primary care physicians with an understanding of the continually evolving field of prostate radiation therapy. Studies of SBRT provide encouraging results of biochemical control and late toxicity. However, they are limited by a number of factors, including short follow–up, exclusion of intermediate– and high–risk patients, and relatively small number of patients treated. Currently, SBRT regimens should only be used in the context of clinical trials.

Nicholas G. Zaorsky, MD (12/11/2012) comments:

Prostate cancer is the second most prevalent solid tumor diagnosed in men in the United States and Western Europe. Besides radical prostatectomy (RP) and brachytherapy (BT), a treatment option for localized prostate cancer includes external beam radiation therapy (EBRT). Stereotactic body radiation therapy (SBRT) is touted as a superior type of EBRT. SBRT has been theorized to be advantageous compared to other RT techniques because it has a treatment course shorter than that of conventionally fractionated EBRT (a single one-hour fraction per day, five days per week, for about two weeks vs. eight weeks), is non-invasive, is more effective at killing tumor cells, and is less likely to damage normal tissue. We reviewed the outcomes and toxicities of current trials of SBRT for prostate cancer.
Freedom from biochemical failure rates for low-, intermediate-, and high-risk patients have generally been ?90% at up to five years. This is an encouraging result that is on par with outcomes from RP, BT, and conventional EBRT approaches. Moreover, less than 4% of patients treated with SBRT had severe (i.e. RTOG Grade 3-4) late toxicity, a result that appears better when compared to conventionally fractionated EBRT studies.
However, these encouraging results have caveats. First, the follow-up times of SBRT studies (mean, 3.1 years) are significantly shorter than those of studies of RP or BT (both, > 5 years). Second, there have been many more patients treated with RP and BT (together, >28,000) than SBRT (<1,000). Third, most of the patients treated in the reported SBRT trials have low-risk disease. Fourth, the almost exclusive use of the RTOG scale to evaluate toxicity precludes the evaluation of significant symptoms, including those of the gastrointestinal tract (e.g. urgency of defecation and fecal incontinence) and sexual dysfunction. Moreover, studies have shown that late toxicity rates tend to increase with follow-up time, so it will be necessary to re-evaluate the SBRT toxicity rates when the data is more mature. Therefore, a number of limitations are still present among all of the trials that preclude recommending SBRT monotherapy for prostate cancer outside the setting of a clinical trial. SBRT should be considered experimental at present.

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