Adjuvant high-dose intensity-modulated radiotherapy (IMRT) after radical prostatectomy for prostate cancer (PCa) is safe and associated with excellent biochemical relapse-free survival (bRFS), according to researchers at Ghent University Hospital in Belgium.

The finding emerged from a study of 104 men who underwent radical prostatectomy followed by adjuvant IMRT at doses above 70 Gy, with or without androgen deprivation. The multidisciplinary team, led by Piet Ost, MD, noted that about 25% of PCa patients who have adjuvant radiotherapy immediately after radical prostatectomy will experience biochemical failure within five years when the conventional 60-64 Gy doses are used.

They conducted the study to see if higher radiation doses can safely improve biochemical outcome.

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“With the advent of IMRT,” they related, “it became feasible to irradiate the prostate bed to a higher dose while sparing critical organs at risk, resulting in less toxicity.”

Subjects had a median follow-up of 36 months. The indications for IMRT were based on the EORTC 22911 trial and included capsule perforation, seminal vesicle invasion (SVI), and/or positive surgical margins. Androgen deprivation was initiated on the basis of SVI, a preprostatectomy PSA level higher than 20 ng/mL, a Gleason sum of 4+3 or higher, or personal preference of the referring urologist. The median prescribed radiation dose was 74 Gy.

The three- and five-year actuarial bRFS was 93%, the researchers reported in European Urology (2009;56:669-677). Seven patients (7%) experienced biochemical relapse, defined as a PSA increase greater than 0.2 ng/mL above the lowest postoperative value measure. The relapses occurred at a mean and median of 24 and 18 months, respectively.

With regard to acute toxicity (defined as an increase of radiation-induced toxicity during or within three months of the end of IMRT), no patient experienced grade 3 gastrointestinal (GI) toxicity, but grade 3 genitourinary (GU) toxicity developed in eight patients (8%), six of whom recovered within three months.

With respect to late toxicity (defined as an increase of radiation-induced toxicity starting at least six months after IMRT or as any acute toxicity lasting more than three months), no patient experienced grade 3 GI toxicity; grade 3 GU toxicity developed in four patients (4%). The investigators observed urethral stricture in six patients (6%).

The authors acknowledged that the median follow-up of 36 months in their study is too short to draw final conclusions on biochemical control.