Room: Exhibit Hall
Purpose: To evaluate the urethral dosimetry for patients treated with high-dose-rate (HDR) tandem and ovoid brachytherapy as an adjuvant therapy to external beam radiation therapy (EBRT) for cervical cancer.
Methods: Twenty patients were retrospectively identified that received HDR T&O brachytherapy as an adjuvant therapy to whole pelvis EBRT. Patients were treated to an EBRT dose of 45Gy/25 fractions delivered to the whole pelvis followed by 30Gy/5 fractions of HDR T&O brachytherapy. All of the patients received concurrent weekly cisplatin-based chemotherapy and underwent CT-image based brachytherapy treatment planning for each insertion. Planning and dose-volume thresholds for target and organs-at-risk were according to published guidelines for cervix brachytherapy. The urethra was identified via the Foley catheter which was contoured with a 2 mm margin to account for its epithelial lining. Mean and maximal doses (0.1 cc) to the urethra were recorded. Cumulative EBRT and brachytherapy doses were then converted to EQD2Gy.
Results: The median urethral volume was 1.8 cc, with a range of 1.2 cc to 2.1 cc. Total brachytherapy dose was 30 Gy in 5 fractions (EQD2Gy 54 Gy in 5 fractions). This resulted in a median combined EQD2Gy for external beam and HDR treatment to 0.1cc and 1.0 cc of urethra of 59.4 Gy (range, 50.4 â€“ 81.0 Gy) and 49.0 Gy (range, 44.5 â€“ 57.9 Gy) respectively.
Conclusion: This study is among the first to assess urethral dosimetry for patients treated with HDR tandem and ovoid brachytherapy for cervical cancer. Despite limited data guiding urethral dose constraints, studies have suggested an increased risk of urethral toxicity in patients with a combined urethral EQD2Gy of >85 Gy. Our median EQD2Gy was below this level but with a wide range, indicating variation in patient anatomy and plan optimization.