Dosimetric factors predicting severe radiation-induced bowel complications in patients with cervical cancer: combined effect of external parametrial dose and cumulative rectal dose

Objective. The purpose of this study was to analyze dosimetric factors of radiation-induced severe bowel complications among patients with cervical cancer. Methods. We reviewed 297 patients of stage IB-IVA cervical cancer managed by curative-intent radiotherapy from May 1993 through December 1997. Whole-pelvic irradiation of external beam radiation therapy (EBRT) (34.2-48.6 Gy/19-27 fractions) was delivered to all patients. Two hundred and three patients received additional bilateral parametrial boost (3.6-18 Gy/2-10 fractions). High dose-rate (HDR) intracavitary brachytherapy (ICBT), 16-24 Gy/5 fractions to Point A, was given after external irradiation. Cumulative rectal biologically effective dose (CRBED) at rectal reference point was determined by summation of EBRT and ICBT component. Results. The 5-year incidences of Grade 3-4 enterocolitis and proctitis were 10% and 7%, respectively. Both complications were associated with external parametrial dose (PMD) and CRBED. Interaction of CRBED and PMD was noted in multivariate analysis of enterocolitis (P<0.001) and proctitis (P<0.001). In CRBED 100 Gy(3) group, PMD was an independent factor in enterocolitis (P=0.010) and proctitis (P=0.039). In PMD :greater than or equal to54 Gy group, CRBED was an independent factor in enterocolitis (P=0.003) and proctitis (P=0.036). Patients with both PMD greater than or equal to54 Gy and CRBED greater than or equal to100 Gy(3) had higher incidence of 5-year enterocolitis (26%) (P<0.001) and proctitis (17%) (P<0.001) than other dose groups. Conclusion. Radiation-induced severe bowel complications are association on both high PMD and high CRBED. We do not suggest both external PMD greater than or equal to54 Gy and CRBED greater than or equal to100 Gy(3) for treatment of cervical cancer due to unacceptably high incidence of severe bowel complications. (C) 2004 Elsevier Inc. All rights reserved.