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

Abstract 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 Gy 3 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. Cancer 2005. © 2005 American Cancer Society.