Rajagopalan Malolan S, Kannan Neeta, Kim Hayeon, Houser Christopher J, Beriwal Sushil
Department of Radiation Oncology, University of Pittsburgh Cancer Institute, Pittsburgh, PA15232, USA.
Brachytherapy. 2013 May-Jun;12(3):248-53. doi: 10.1016/j.brachy.2012.10.005. Epub 2013 Mar 1.
The tolerance and complication rates of the urethra are unknown for the interstitial high-dose-rate brachytherapy (HDR-BT) for vaginal cancer.
Patients with vaginal cancer near/involving the urethra who were treated with HDR-BT between 2008 and 2011 were included. Patients received mean external beam dose of 48.0Gy followed by mean HDR-BT dose of 4.5Gy/fraction for five fractions. With CT-based planning, the urethra was contoured from the bladder neck to the meatus. Doses were converted to the biologically equivalent dose in 2Gy/fraction (EQD2).
A total of 16 patients were included, and the EQD2D90 was 74.9Gy. The urethral volume was 1.31cm(3), and the EQD2 to 0.1 and 1cm(3) were 76.2 and 48.9Gy, respectively. Two of the 6 patients with urethral involvement developed urethral necrosis. The D90 for these 2 patients was 76.8Gy, and the urethral doses to 0.1 and 1cm(3) were 95.1 and 45.8, respectively. Those who developed severe urethral toxicity had a trend to urethral EQD2 (95.1Gy vs. 73.4Gy, p=0.1) and significantly higher dose per fraction of HDR-BT to 0.1cm(3) of the urethra (5.7Gy vs. 3.7Gy, p=0.02) when compared with those who did not develop severe urethral toxicity.
This study is among the first to assess urethral dosimetry for patients treated with HDR-BT for vaginal cancer. Patients who received five fractions of higher than 5Gy/fraction to 0.1cm(3) of urethra (estimated EQD2 of 85Gy) are at increased risk of severe urethral toxicity.
阴道癌间质高剂量率近距离放射治疗（HDR - BT）的尿道耐受性和并发症发生率尚不清楚。
纳入2008年至2011年间接受HDR - BT治疗的阴道癌靠近/累及尿道的患者。患者平均外照射剂量为48.0Gy，随后平均HDR - BT剂量为4.5Gy/分次，共5次。采用基于CT的计划，从膀胱颈到尿道口勾勒出尿道轮廓。剂量转换为2Gy/分次的生物等效剂量（EQD2）。
共纳入16例患者，EQD2D90为74.9Gy。尿道体积为1.31cm³，0.1cm³和1cm³的EQD2分别为76.2Gy和48.9Gy。6例尿道受累患者中有2例发生尿道坏死。这2例患者的D90为76.8Gy，0.1cm³和1cm³的尿道剂量分别为95.1Gy和45.8Gy。与未发生严重尿道毒性的患者相比，发生严重尿道毒性的患者尿道EQD2有升高趋势（95.1Gy对73.4Gy，p = 0.1），且尿道0.1cm³的HDR - BT每次剂量显著更高（5.7Gy对3.7Gy，p = 0.02）。
本研究是首批评估接受HDR - BT治疗的阴道癌患者尿道剂量学的研究之一。接受5次高于5Gy/分次剂量照射至尿道0.1cm³（估计EQD2为85Gy）的患者发生严重尿道毒性的风险增加。
