De-escalation of the cumulative central radiation dose according to the tumor response can reduce rectal toxicity without compromising the treatment outcome in patients with uterine cervical cancer

Objective To assess the treatment outcome and toxicity of a low cumulative central dose using a midline block (MLB) during external beam radiotherapy (EBRT). Methods Between January 1988 and December 2010, 1559 patients with FIGO stage IB-IIB uterine cervical cancer that underwent EBRT and high-dose-rate intracavitary brachytherapy (HDR-ICBT) were retrospectively analyzed. During EBRT, MLB was performed (n = 1195, MLB group) when a sufficient response was achieved to insert the tandem through the cervical canal and place ovoids in the vaginal cavity. MLB was not applied for patients with a slow tumor response (n = 364, non-MLB group). The doses were estimated according to the International Commission on Radiation Units and Measurements (ICRU) points. The biologically equivalent dose in 2-Gy fractions (EQD2) was calculated to estimate the cumulative dose from EBRT and ICBT. Results EQD2_pointA, EQD2_rectum, and EQD2_bladder were all significantly lower in the MLB group (all P < 0.05). The 10-year grade ≥ 2 late rectal toxicity rate was significantly lower in the MLB group (P = 0.012), while there was no significant difference in late genitourinary and small bowel toxicity. ICRU rectal and bladder doses showed significant predictability on late rectal and bladder toxicities. After propensity score matching, all patient and tumor characteristics were well matched and the survival and recurrence rates between the two groups were similar (all P > 0.05), despite the lower EQD2_pointA in the MLB group (P < 0.001). Conclusions Applying MLB according to tumor response during EBRT lowered the cumulative central dose and reduced late rectal toxicity without compromising treatment outcome.