Hypofractionated IMRT does not increase sexual side effects

LOS ANGELES—Compared with conventional intensity-modulated radiation therapy for prostate cancer, hypofractionated IMRT is not associated with any increase in sexual adverse effects, finds a randomized trial.

“Hypofractionation exploits the hypothesized late-responding nature of prostate cancer,” Mark K. Buyyounouski, MD, said at ASTRO 2007 (abstract 13). “Preliminary results of hypofractionation suggest that IMRT may limit GI and GU toxicity. IMRT may also limit the development of sexual dysfunction if the erectile tissues are sufficiently spared.”

Dr. Buyyounouski and his colleagues at Fox Chase Cancer Center assigned men with intermediate- to high-risk prostate cancer to conventional IMRT (76 Gy in 38 fractions) or hypofractionated IMRT (70.2 Gy in 26 fractions, hypothesized to be equivalent to 84.4 Gy in 2-Gy fractions). Analyses presented at the meeting were restricted to men with intermediate-risk disease who did not receive androgen-deprivation therapy. Sexual function was assessed using the Expanded Prostate Cancer Index Composite (EPIC) questionnaire.

Analyses were based on 78 men in the conventional IMRT group and 79 in the hypofractionated IMRT group (median follow-up, 28 months).

At baseline, the sexual function (SF) score (the weighted average of the 13-question sexual function domain of EPIC) mean value did not differ between the groups (52 vs 52 on a scale of 0-100, with higher scores indicating better function). Overall, one-fifth of men had a SF score of 70 of higher, and one-half had a score of 38 or higher.

No difference in SF score

In both groups, mean sexual function scores decreased from baseline with follow-up, but the difference in scores between groups remained nonsignificant at 6, 12, and 24 months, he said.

In univariate analysis, the type of IMRT received was not significantly associated with the risk of having a sexual function score of less than 70 or less than 38. The findings were the same in a multivariate analysis in which only lower baseline sexual function score independently predicted a lower score with follow-up.

In further analyses, the proportion of men experiencing an erection at least some of the time when desired and the proportion experiencing erections firm enough for sexual activity did not differ between the the two groups at 6, 12, or 24 months.

The proportion of men experiencing any nocturnal tumescence did not differ at 6 and 12 months, but was significantly greater with conventional IMRT at 24 months (71% vs 46%). However, this difference was also present at baseline (74% vs 57%), Dr. Buyyounouski noted.

“In conclusion, within the limits of this analysis, sexual function was not adversely affected by hypofractionation doses calculated to be equivalent to

84.4 Gy in 2-Gy fractions when compared with 76 Gy in 38 fractions. Whether the hypofractionated regimen confers a benefit for disease control will be the subject of future planned analyses,” Dr. Buyyounouski said.

He noted that hypofractionation remains investigational at Fox Chase. “We have not yet adapted this technique to treat patients outside of the study setting,” he said.