Analysis of correlation between rectal complications and rectal dose following high dose rate intracavitary radiotherapy in patients with uterine cervix cancer: in vivo dosimetric analysis.

Purpose: To investigate the correlation between late rectal complications and rectal dose in uterine cervix cancer patients treated with high dose rate intracavitary radiotherapy (HDR ICR) and to analyze dose factors reducing complications. Methods: A retrospective analysis was done of 74 patients treated with external beam RT and HDR ICR between 1995 and 1997. Radiotherapy (RT) consisted of a median 50.4 Gy external beam plus six fractions of HDR ICR given two times per week, concurrent with the last three weeks of external beam therapy, to a total dose of median 24 Gy to point A or the reference point. Rectal doses were calculated at rectal reference points using barium contrast criteria. In vivo measurement of rectal dose was performed with thermoluminescent dosimeters (TLD) immediately prior to the first fraction of HDR ICR. Results: Eight patients developed rectal complications (11%). There was a significant difference between measured rectal doses for patients with rectal complications and those without (p <0.05), and the doses were higher in complicated patients. A significant increase in the probability of development of complications was found for patients receiving measured rectal doses of ICR fractional dose 320 cGy or more, ICR total dose 2000 cGy or more, and ICR % to point A 80% or more. Conclusions: This study showed that in vivo dosimetry using TLD during HDR ICR could have a useful role as a predictor of late rectal complications. Dose limitation to the rectum could possibly be achieved by thorough vaginal packing or use of an applicator with proper shielding while maintaining a high dose to the tumor.