Effect of high-dose-rate 192Ir source activity on late rectal bleeding after intracavitary radiation therapy for uterine cervix cancer

Purpose: This retrospective study analyzed the effect of the activity of high-dose-rate (HDR) Ir-192 source on late rectal bleeding after HDR intracavitary radiotherapy (ICRT) in patients with uterine cervix cancer. Methods and Materials: One hundred thirty-two patients who underwent HDR-ICRT and external beam radiotherapy (EBRT) were analyzed. The rectal point dose in ICRTwas calculated by inserting a lead wire into the rectal lumen and summed with the whole-pelvic EBRT dose. The rectal biologic effective dose (BED) was calculated. The relationship between averaged source activity or the BED and late rectal bleeding were analyzed. Results: Three-year actuarial rectal bleeding probabilities were 46% (>= 100 Gy(3)) and 18% (<= 100 Gy(3)) respectively (p < 0.005). When patients were divided into four groups according to rectal BED (>= or <= 100 Gy(3)) and source activity (>= or <= 2.4 cGy.m(2).h(-1)), the group with both a high BED and high activity showed significantly greater probability (58% at 3 years; p < 0.005). It was noted that 2 the probability of the group with BED of 100 Gy(3) or greater was high, but that was not the case with 2.4 cGy.m(2).h(-1) or less. Conclusion: This is the first clinical report concerning the source activity effect of HDR Ir-192 on late rectal bleeding in patients undergoing HDR-ICRT. This suggests that when source activity is higher than 2.4 cGy.m(2).h(-1), ICRT should be performed with more caution not to exceed 100 Gy(3) in total. (c) 2008 Elsevier Inc.