title: Urethral dosimetry and toxicity with high-dose-rate interstitial brachytherapy for vaginal cancer.
abstract: OBJECTIVE
  The tolerance and complication rates of the urethra are unknown for the interstitial high-dose-rate brachytherapy (HDR-BT) for vaginal cancer.
  
  
  METHODS
  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).
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors: Department of Radiation Oncology, University of Pittsburgh Cancer Institute, Pittsburgh, PA15232, USA.
authors: Malolan S
authors: MS
authors: Rajagopalan
authors: Neeta
authors: N
authors: Kannan
authors: Hayeon
authors: H
authors: Kim
authors: Christopher J
authors: CJ
authors: Houser
authors: Sushil
authors: S
authors: Beriwal
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001918:Brachytherapy / Q000009:adverse effects* / Q000379:methods; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D010414:Pennsylvania / Q000453:epidemiology; D011832:Radiation Injuries / Q000175:diagnosis* / Q000453:epidemiology; D011879:Radiotherapy Dosage; D012189:Retrospective Studies; D014521:Urethra / Q000528:radiation effects*; D014625:Vaginal Neoplasms / Q000532:radiotherapy*