309. Dosimetric evaluation of urethral toxicity in postoperative adaptive intracavitary High-Dose-Rate brachytherapy for endometrial carcinoma

Published on Dec 1, 2018in Physica Medica2.485
· DOI :10.1016/J.EJMP.2018.04.318
L. Milan (University of Milan), C. Bianchi10
Estimated H-index: 10
+ 2 AuthorsRaffaele Novario15
Estimated H-index: 15
(University of Insubria)
Purpose To evaluate the urethral tolerance in postoperative adaptive endocavitary High-Dose-Rate brachytherapy (HDR-BT) in endometrial adenocarcinoma (EADK), correlating local toxicity with urethral dose and HDR-BT parameters. Methods Between 2012 and 2017, 29 post-hysterectomy EADK patients were consecutively treated with endocavitary HDR-BT. The median total dose was 35.0 (21.0–41.5) Gy delivered in 6 (3–6) fraction of median 6.5 (5.5–7.0) Gy. Urethra was contoured on CT-images acquired before any BT fraction. Median urethral volume was 3.5 (1.7–6.4) cc. Measured median dose/fraction to 0.1 cc and 1 cc of urethra were 7.8 (1.5–11.8) Gy [EQD2 = 17.0 (1.3–34.9) Gy] and 5.7 (0.9–8.1) Gy [EQD2 = 9.8 (0.7–18.1) Gy], respectively. HDR-BT parameters evaluated were: dose/fraction, total dose, dose to 0.1 cc and 1 cc of urethra, relative and absolute urethral volume covered by 50% and 100% of prescribed dose. Results 5 patients (17%) developed acute transient urethral toxicity (4-G1; 1-G2). No late sequelae were diagnosed with a median follow-up of 34 (8–64) months. In order to evaluate the possible correlation between HDR-BT parameters and observed urethritis, we analyzed the subgroup of patients with manifested toxicity. They showed equivalent urethral volume (p = 0.80) and EQD2 to 0.1 cc (p = 0.41) respect to asymptomatic patients. Table 1 reports comparing data: no significant differences emerged between this subgroup and controls. We stressed that, even if the p-value for urethra volume covered by 50% of prescribed dose is low, this parameter cannot be used as discriminating value (Fig. 1). Conclusions This study is the first to retrospectively investigate urethral toxicity in postoperative endocavitary HDR-BT. 5 out of 29 patients developed acute transient urethritis without any sequelae. There was no evident correlation between this complication and HDR-BT dosimetric parameters. Urethral toxicity seems only patient-related.
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