Although many published studies describe SBRT, several limitations in the available literature raise concerns about the widespread use of SBRT. To date, no published comparative studies (either randomized or nonrandomized prospective studies) have addressed the relative effectiveness and safety of SBRT versus other forms of external-beam radiation therapy. Also, SBRT seems to be widely disseminated for treatment of various cancer types, although most of the studies (n = 68) were for SBRT for tumors located in the lung or thorax. We found fewer than 10 studies each of tumors of the pancreas, liver, colon, uterus, pelvis, sacrum, kidney, and prostate. A Medicare Evidence Development and Coverage Advisory Committee proceeding from April 2010 considered the evidence for radiation therapy for localized prostate cancer (117). The panel of 15 experts was asked to state its level of confidence in the evidence for improvement of mortality (survival and death rates), functional outcomes (erectile dysfunction, urinary incontinence, and fecal incontinence), and adverse events (rectal fistula, radiation burns, and infection) with SBRT compared with classical fractionated external-beam radiation therapy for localized prostate cancer. On a scale of 1 (low confidence) to 5 (high confidence), the average score was 1.07 for mortality, 1.13 for functional outcomes, and 1.33 for adverse events (117).