Combined treatment with intensity-modulated radiation therapy (IMRT) and brachytherapy provides better oncologic outcomes than high-dose IMRT alone in patients with intermediate-risk prostate cancer (PCa), researchers concluded in an online report in BJU International.

Acute genitourinary (GU) toxicities occurred more frequently with the combination treatment, but the incidence of late GU and gastrointestinal (GI) toxicities with both approaches was similar.

Michael J. Zelefsky, MD, and colleagues at Memorial Sloan-Kettering Cancer Center in New York studied 870 patients with intermediate-risk PCa treated with either 86.4 Gy of IMRT alone (470 patients) or 50.4 Gy of IMRT plus brachytherapy (combo-RT, 400 patients). The median follow-up for the entire cohort was 5.3 years.

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The seven-year actuarial PSA relapse-free survival (PSA-RFS) and distant metastases-free survival (DMFS) rates were 81.4% and 93.0%, respectively, for IMRT-only recipients compared with 92.0% and 97.2%, respectively, for the combo-RT group, Dr. Zelefsky’s group reported. The differences in the survival rates between the groups were statistically significant. On multivariate analysis, combo-RT was associated with a 60% and 59% decreased likelihood of PSA relapse and metastatic disease, respectively.

Acute GU grade 2 and grade 3 toxicities developed in 35.8% and 2.3%, respectively, of the combo-RT group compared with 18.9% and 0.4%, respectively, of the IMRT-only group. The differences between the groups were statistically significantly.

The seven-year actuarial late toxicity rates in the IMRT-only and combo-RT groups were 4.6% and 4.1% for grade 2 GI toxicity, respectively, 0.4% and 1.4% for grade GI toxicity, 19.4% and 21.2% for grade 2 GU toxicity, and 3.1% and 1.4% for grade 2 GU toxicity. None of the between-group differences in these rates was statistically significant.

“The present study is the first to show superior PSA-RFS and DMFS outcomes for patients with intermediate-risk prostate cancer treated with a combined brachytherapy and IMRT regimen compared with those treated with high-dose IMRT,” the authors wrote.

The researchers pointed out that previous randomized trials comparing a brachytherapy-based boost regimen with external beam radiotherapy (EBRT) alone have been limited by the inclusion of patients treated with lower doses of EBRT, which could have resulted in a greater percentage of failures. The present study compared a combined brachytherapy regimen with dose-escalated IMRT, and still demonstrated improved outcomes with the combined regimen.

The authors indicate that these improved outcomes may be related to the intense dose escalation associated with brachytherapy-based regimens, which was likely associated with better control of intra-prostatic disease.