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31-08-2018 | Prostate cancer | News

Moderately hypofractionated radiotherapy regimen promising for localized prostate cancer

medwireNews: Intensity-modulated radiation therapy (IMRT) using a moderately hypofractionated, dose-escalated regimen may control localized prostate cancer better than a conventional regimen while shortening treatment duration, a phase III trial suggests.

Among 206 men with organ-confined prostate cancer, those who were randomly assigned to receive the hypofractionated (H)IMRT regimen were significantly less likely to experience the primary endpoint of treatment failure than those receiving conventionally fractionated (C)IMRT during a median follow up of 8.5 years.

Treatment failure, defined as biochemical failure (prostate specific antigen [PSA] nadir plus 2 ng/mL) or the initiation of salvage therapy, occurred in 10 of the 104 men receiving HIMRT versus 21 of the 102 men receiving CIMRT. The cumulative incidence of failure at 8 years was 10.7% with HIMRT versus 15.4% with CIMRT. Overall survival did not differ in the two groups.

The HIMRT regimen delivered 72.0 Gy in 2.4 Gy fractions over 6 weeks while the CIMRT regimen delivered 75.6 Gy in 1.8 Gy fractions delivered over 8.4 weeks.

The researchers point out that although HIMRT resulted in a “higher biologically effective treatment dose,” the regimen did not increase the incidence of late urinary toxicity, with grade 2 or 3 events occurring in a respective 15.1% and 16.4% of patients in the HIMRT and CIMRT groups over 8 years.

The incidence of late grade 2 and 3 gastrointestinal toxicity (mostly rectal bleeding) was higher with the dose-escalated hypofractionated regimen than with CIMRT, at 12.6% versus 5.0%, but this difference was not statistically significant.

Furthermore, all cases of rectal bleeding resolved with treatment, say the study authors who also note that the 8-year rate of gastrointestinal side effects was just 8.6% when a radiation dose of 65 Gy or more was delivered to no more than 15% of the rectal volume, thereby providing a means of reducing the bleeding risk.

Of note, there were no grade 4 genitourinary or gastrointestinal adverse events in either treatment arm, Karen Hoffman (University of Texas MD Anderson Cancer Center, Houston, USA) and colleagues report in the Journal of Clinical Oncology.

They continue: “It should be noted that this trial was conducted in the early days of IMRT and image-guided radiation therapy. Delivery of contemporary radiotherapy that uses smaller [planning target volume] expansions has the ability to reduce [the] dose delivered to the rectum and bladder and may produce better toxicity outcomes.”

By Anita Chakraverty

medwireNews is an independent medical news service provided by Springer Healthcare. © 2018 Springer Healthcare part of the Springer Nature group

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