There are radiobiological rationales supporting hypofractionated radiotherapy for prostate cancer. The recent advancements in treatment planning and delivery allow sophisticated radiation treatments to take advantage of the differences in radiobiology of prostate cancer and the surrounding normal tissues. The preliminary results from clinical studies indicate that abbreviated fractionation programs can result in successful treatment of localized prostate cancer without escalation of late toxicity. 1. Introduction Prostate cancer is the most common cancer diagnosed in American men after non-melanomatous skin cancer. According to the American Cancer Society estimate, there will be more than 241,000 new cases of prostate cancer in the United States in 2012. Approximately 28,000 men in the USA will die of prostate cancer, making it the second leading cause of cancer death in this country [1]. In most cases the prostate cancer is organ-confined at the time of initial diagnosis [2]. Radical prostatectomy and radiotherapy, either given as a seed implant or external beam radiation therapy, are the accepted standard options for treating the primary tumor itself, and androgen deprivation may be added selectively for certain cases with an intermediate or high risk of dissemination based on clinical and pathologic features evident at the time of diagnosis. Regarding the specific option of external beam radiotherapy, the current widely accepted standard regimen for organ-confined prostate cancer in the USA involves approximately eight weeks of fractionated treatments with a daily dose of 1.8–2.0？Gy to a total dose in the range of 70–80？Gy. At some centers the treatments, also called fractions, are given over 9-10 weeks [3]. Although many patients have been successfully treated with radiotherapy regimens of this nature, the optimal radiation schedule for the curative treatment of prostate cancer remains an unsettled question. For patients with clinical features suggesting at least an intermediate level of aggressiveness, a moderate dose escalation has been demonstrated to improve biochemical control with acceptable toxicity using contemporary radiotherapy techniques [4, 5]. Unfortunately, dose escalation using a conventionally fractionated treatment schedule requires a lengthened treatment course that is less convenient for patients and more costly for government and private insurance carriers. Emerging evidence accumulating from multiple recent studies indicates that more convenient and efficient shortened courses of radiotherapy for prostate cancer yield outcomes
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