Clinical effect of multileaf collimator width on the incidence of late rectal bleeding after high-dose intensity-modulated radiotherapy for localized prostate carcinoma.

BACKGROUND: Several studies have confirmed a dosimetric advantage associated with use of a smaller leaf in intensity-modulated radiation therapy (IMRT). However, no studies have identified any clinical benefits. We investigated the effect of a smaller multileaf collimator (MLC) width on the onset of late rectal bleeding after high-dose prostate IMRT.
MATERIALS AND METHODS: Two hundred and five prostate cancer patients were treated with a total dose of 78 Gy in 39 fractions by use of a dynamic MLC technique; however, two different MLC were used: a 10-mm-wide device and a 5-mm-wide device. Gastrointestinal toxicity and several clinical factors were assessed.
RESULTS: The 5-year actuarial risk of grade 2 or higher rectal bleeding was 6.9 % for the 10-mm-wide group (n = 132) and 1.8 % for the 5-mm-wide group (n = 73) (p = 0.04). The median estimated rectal doses for the two groups were 55.1 and 50.6 Gy (p < 0.001), respectively. Univariate analysis showed that acute toxicity, rectal V30-60, median rectal dose, normal tissue complication probability (NTCP), and MLC type were significant predictive factors for late rectal toxicity. In multivariate analysis, acute toxicity and NTCP remained significant.
CONCLUSION: In our planning approach for prostate IMRT, a decrease in MLC width from 10 to 5 mm contributed to further rectal dose reduction, which was the most important predictor of late rectal toxicity.