Dosimetric parameters that predict late rectal complications after curative radiotherapy in patients with uterine cervical carcinoma

BACKGROUND. Late rectal complication (LRC) was a major late complication in patients with uterine cervical carcinoma who were treated with a combination of external beam radiotherapy (EBRT) and high-dose-rate intracavitary irradiation (HDR-ICR). For the current study, the authors retrospectively evaluated dosimetric parameters that were correlated with LRC ≥ Grade 2 in patients with uterine cervical carcinoma who were treated with curative radiotherapy, and they analyzed the appropriate dose estimates to the rectum that were predictive for LRC ≥ Grade 2. METHODS. Between July, 1994 and September, 2002, 157 patients who were diagnosed with Stage IB-IIIB cervical carcinoma and were treated with definitive radiotherapy were included. EBRT (41.4-66 grays [Gy] in 23-33 fractions) to the whole pelvis was delivered to all patients, with midline shielding performed after a 36-50.4 Gy external dose. HDR-ICR (21-39 Gy in 6-13 fractions to Point A) was administered at a rate of 2 fractions weekly after midline shielding of EBRT. LRC was scored using Radiation Therapy Oncology Group criteria. The total biologically effective dose (BED) at specific points, such as Point A (BED_{Point A}), rectal point (BED_RP), and maximal rectal point (BED_MP), was determined by a summation of the EBRT and HDR-ICR components, in which the α/β ratio was set to 3. Analyzed parameters included patient age, tumor size, stage, concurrent chemotherapy, ICR fraction size, RP ratio (dose at the rectal point according to the Point A dose), MP ratio (dose at the maximal rectal point according to the Point A dose), EBRT dose, BED_{Point A}, BED_RP, and BED_MP. RESULTS. The 5-year actuarial overall rate of LRC ≥ Grade 2 in all patients was 18.4%. Univariate analysis showed that the RP ratio, MP ratio, EBRT dose, BED_{point A}, BED_RP, and BED_MP were correlated with LRC ≥ Grade 2 (P < 0.05). Multivariate analysis showed that, of all clinical and dosimetric parameters evaluated, only BED_RP was correlated with LRC ≥ Grade 2(P = 0.009). The 5-year actuarial rate of LRC ≥ Grade 2 was 5.4% in patients with a BED_RP < 125 Gy ₃ and 36.1% in patients with a BED_RP ≥ 125 Gy ₃ (P < 0.001). CONCLUSIONS. BED_RP was a useful dosimetric parameter for predicting the risk of LRC ≥ Grade 2 and should be limited to < 125 Gy₃ whenever possible to minimize the risk of LRC ≥ Grade 2 in patients with uterine cervical carcinoma who are treated with a combination of EBRT and HDR-ICR.