ASCO guidelines recommend that brachytherapy boost, either with LDR or HDR, should be offered to eligible patients with intermediate and high risk prostate cancer. This is based on results of three randomized clinical trials, all showing improved cancer control rates with the addition of brachytherapy. The Canadian multicenter ASCENDE-RT clinical trial randomized men with unfavourable risk localized prostate cancer to either 32 Gy external beam radiotherapy or an iodine-125 implant of 115 Gy, following pelvic radiotherapy to a dose of 46 Gy. All received a total of 12 months androgen deprivation therapy. Brachytherapy boost was associated with a 54% reduction in risk of biochemical failure, an absolute difference of over 20% at 9 years (17% vs. 38%). There was more toxicity in the brachytherapy arm with a cumulative incidence of grade 3 urinary toxicity of 19% vs. 5%, and 5-year prevalence of 9% vs. 2%. It is likely that the high urethral stricture rate was partly related to implant technique and can be reduced by limiting dose to membranous urethra or by use of HDR. Unanswered questions include the optimal duration of androgen deprivation therapy, role of pelvic radiotherapy, and need for other systemic options.
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