Postoperative endometrial carcinoma treated with external beam irradiation plus vaginal-cuff brachytherapy. Is there a dose relationship with G2 vaginal complications?

Abstract

To analyse the possible relationship between the EQD2(α/β=3Gy) at 2cm3 of the vagina and late toxicity in vaginal-cuff-brachytherapy (VBT) after external-beam-irradiation (EBRT) for postoperative endometrial carcinoma (EC). From 2014 to 2016, 62 postoperative EC patients were treated with EBRT+VBT. The median EBRT dose was 45Gy (44Gy-50.4Gy). VBT involved a single 7Gy dose. Toxicity was prospectively evaluated using the RTOG score for the rectum and bladder and the objective LENT-SOMA criteria for the vagina. EQD2(α/β=3Gy) at 2cm3 of the most exposed part of the vagina was calculated by the sum of the EBRT+VBT dose. Statistics: Boxplot, Student's t and Chi-square tests and ROC curves. Mean follow-up: 39.2 months (15-68). Late toxicity: bladder:0 patient; rectum:2 patients-G1; Vagina: 26 patients-17G1, 9G2; median EQD2(α/β=3Gy) at 2cm3 in G0-G1 patients was 70.4Gy(SD2.36), being 72.5Gy(SD2.94) for G2p. The boxplot suggested a cut-point identifying the absence of G2: 100 % of G2p received >68Gy, ROC curves showed an area under the curve of 0.72 (sensitivity of 1 and specificity of 0.15). Doses >68Gy EQD2(α/β=3Gy) at 2cm3 to the most exposed area of the vagina were associated with late G2 vaginal toxicity in postoperative EC patients treated with EBRT+VBT suggesting a very good dose limit to eliminate the risk of G2 late toxicity. The specificity obtained indicates the need for prospective analyses.