Uterosacral space involvement in locally advanced carcinoma of the uterine cervix

Abstract

Radiation therapy is the standard management for locally advanced cervical cancer, but it has not yielded fully satisfactory results; a relatively high incidence of local failure remains. Standard radiation therapy techniques combine external beam radiation and brachytherapy generating a homogeneously composite dose distribution covering the lateral parametria but may not be adequate in the uterosacral and perirectal areas due to the spatial arrangement of intracavitary system and the constraints of rectal tolerance. We hypothesize that these dosimetric characteristics might lead to a higher incidence of central/marginal failures when the uterosacral space is involved by locally advanced carcinoma of uterine cervix. Between January 1970 and December 1989, 343 patients with clinical Stage IIIB cervical cancer were treated at the Mallinckrodt Institute of Radiology with radiation therapy alone. We identified 83 patients with clinical evidence of tumor in the uterosacral region; the remaining 260 patients either did not have uterosacral involvement or were unspecified. The dose of external beam irradiation ranged from 18.02 to 33.20 Gy to the central pelvis and 48.22 to 59.40 Gy to the lateral parametrium. The average total dose, including brachytherapy contribution, to point A and the lateral pelvis was 80.30 to 86.46 Gy and 60.50 to 73.40 Gy, respectively. External beam dose to the lateral parametria was, on average, 10 Gy higher in patients with uterosacral involvement. We categorized the patterns of pelvic failure into central/marginal (including medial parametrium) and lateral parametria. The cumulative incidence of central/marginal failure at 5 years was significantly higher in the group of patients with uterosacral involvement (36% compared with 21% for patients without uterosacral involvement or unspecified) (p = 0.002). Lateral parametrial failure was similar for patients with and without uterosacral involvement (39% and 38% at 5 years, respectively) (p = 0.42). The actuarial incidence of distant metastasis was identical in the two groups: 46% at 5 years. Multivariate analysis confirmed that uterosacral space involvement increased the risk of pelvic recurrence (p = 0.044) and was the most significant factor that influenced the central/marginal pelvic failure (p = 0.002). Uterosacral involvement by locally advanced carcinoma of the uterine cervix significantly increased overall pelvic failure and was the most significant prognosticator of central/marginal pelvic failure. This is the result of the spatial constraints of the standard intracavitary geometry that deliver inadequate dose posteriorly to encompass the uterosacral space. Plausible ways to compensate the underdose in the uterosacral space include increasing whole pelvis dose without compromising the intracavitary brachytherapy dose, using a supplemental interstitial implant or adding a posterior oblique external beam boost.