Low dose-rate (LDR) brachytherapy has emerged as a preferred treatment option for many men with low and intermediate risk prostate cancer. High dose-rate (HDR) brachytherapy has potential advantages including less short-term toxicity and more consistent dosimetry. Mature data using 3, 4 or 6 fractions reports equally good long-term cancer control rates with little toxicity. Delivering multiple fractions, however, is logistically challenging, inconvenient for patients, costly, and resource intensive. In recent years there has been interest in exploring more hypofractioned HDR monotherapy regimens involving two or single fractions, taking advantage of prostate cancer’s low alpha/beta ratio. We have completed a randomized clinical trial of HDR monotherapy delivered as either a single fraction of 19 Gy, or as two fractions of 13.5 Gy delivered one week apart. We have found both regimens to be very well tolerated, with less urinary and sexual toxicity in the single fraction arm during the first 12 months. It remains uncertain if single 19 Gy provides sufficiently high cancer control rates, and current direction is to further escalate the single fraction dose using intra-prostatic boosting. An ongoing Canadian randomized trial is comparing single fraction HDR with a standard iodine-125 LDR implant.
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