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Change in radiation dose distribution may reduce late rectal bleeding
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Men with shorter rectums who receive intermediate to high doses of radiation are more likely to experience rectal bleeding following radiation treatment for prostate cancer, according to study findings presented at the Annual Meeting of the American Association of Physicists in Medicine.
Thus, considering rectum length and radiation therapy dose may help predict a patient’s risk for experiencing late rectal bleeding, which occurs in approximately one in 10 men with prostate cancer who undergo radiation, according to the researchers.
“Radiation dose distribution can be designed for each individual patient, and while it covers the prostate, it often comes in contact with the rectum or the bladder too,” study researcher Joseph O. Deasy, PhD, chair of the department of medical physics at Memorial Sloan Kettering Cancer Center, said during a press conference. “By reducing the dose to the edge of the area being irradiated in men with shorter rectums, possibly using better treatment image guidance, we can significantly reduce the risk of late-stage rectal bleeding.”
The researchers identified 1,001 men who were treated with a variety of radiation therapy techniques for prostate cancer (922 had 3-D conformal radiation therapy; 211 had image-guided radiation therapy and 79 had intensity-modulated radiation therapy). The men received between 70 Gy to 86 Gy at 2 Gy per fraction between 1991 and 2007 at five participating hospitals.
The median follow-up for late rectal bleeding was 58 months (range, 4-259). Using the Mann-Whitney test, the researchers compared the rectal cross-sectional area, length and volume between patients with late rectal bleeding and those without.
Data showed patients with late rectal bleeding had significantly smaller (mean, 48 cm vs. 68 cm) and shorter (mean, 6 cm vs. 7 cm) rectums than those patients who did not experience late rectal bleeding (P < .01 for both).
Results of a univariate analysis indicated relative volumes receiving between 5 Gy and 20 Gy (Rs = 0.05-0.07), relative volume receiving between 40 Gy and 65 Gy (Rs = 0.05-0.11), the minimum dose to the hottest 20% to 55% volumes and 100% volumes (Rs = 0.06-0.09) and mean dose (Rs = 0.05) significantly predicted late rectal bleeding (P < .03).
Results of a multivariate analysis indicated length, relative volumes receiving 50 Gy, mean dose, and minimum dose to the hottest 35% volumes all significantly predicted late rectal bleeding (P ˂ .01).
“The rate of rectal bleeding was lower in those patients with intensity-modulated radiation therapy,” Deasy said. “We’re not able to understand why it’s so good yet, but ongoing research is trying to find out. Meanwhile, this formula, which has more sculpting of the resolution in the dose distribution, potentially could be put into treatment planning systems that are routinely used.” – by Anthony SanFilippo
Reference: Thor M, et al. Abstract 29613. Presented at: Annual Meeting of the American Association of Physicists in Medicine; July 12-16, 2015; Anaheim, California.
Disclosure: HemOnc Today was unable to obtain a list of relevant financial disclosures.