Late rectal complication following high dose rate intracavitary brachytherapy in cancer of the cervix.

PURPOSE: To examine the incidence of radiation-induced late rectal complications using a rectal reference point in patients with cancer of the uterine cervix. METHODS AND MATERIALS: The subjects were 253 patients with cancer of the cervix who underwent high dose rate intracavitary brachytherapy (HDR-ICR). The rectal point (RP) was defined according to the criteria recommended in the ICRU Report 38. The time-dose factor (TDF) and the biologically effective dose (BED) were calculated as components of the cumulative reference rectal dose using the rectal reference point dose in intracavitary brachytherapy combined with the external whole pelvis dose. RESULTS: Statistical comparison of factors affecting the incidence of late rectal complication was conducted using data for 161 patients. The incidence of late rectal complications in the 161 patients was 9 patients (5.6%) for grade 1, 51 patients (31.7%) for grade 2, 11 patients (6.8%) for grade 3, and 13 patients (8.1%) for grade 4. The TDF and BED values were significantly correlated with the incidence of late rectal complication, and also showed strong correlation (r = 0.976) with each other. Grade 4 rectal complication was not observed in any patients with TDF below 130 or BED below 147. The calculated incidence of complications ranged from 5 to 10% at TDF values from 104 to 124 and at BED values from 119 to 146. CONCLUSION: These data regarding the incidence of rectal complication may be useful in reducing the incidence of late rectal complications arising after HDR-ICR treatment of cervical uterine cancer by adjusting the dose per fraction and number of fractions of HDR-ICR in individual patients and by improving the technique of inserting the intracavitary radiation apparatus.