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

Authors


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 (BEDPoint A), rectal point (BEDRP), and maximal rectal point (BEDMP), 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, BEDPoint A, BEDRP, and BEDMP.

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, BEDPoint A, BEDRP, and BEDMP were correlated with LRC ≥ Grade 2 (P < 0.05). Multivariate analysis showed that, of all clinical and dosimetric parameters evaluated, only BEDRP 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 BEDRP < 125 Gy3 and 36.1% in patients with a BEDRP ≥ 125 Gy3 (P < 0.001).

CONCLUSIONS

BEDRP 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. Cancer 2005. © 2005 American Cancer Society.

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