title: High-dose-rate brachytherapy of rhabdomyosarcoma limited to the external auditory canal.
abstract: To report on the single-catheter high-dose-rate brachytherapy treatment of a 21-month-old girl child with an embryonal, botryoid-type, rhabdomyosarcoma limited to the external auditory canal (EAC).
  
  
  
  A 2.4-mm diameter catheter was inserted into the right EAC and placed against the tympanic membrane. A computed tomography simulation scan was acquired. A brachytherapy treatment plan, in which 21 Gy in seven fractions was prescribed to a 1-mm depth along the distal 2 cm of the catheter, was generated. Treatments were delivered under anesthesia without complication. A dosimetric comparison between this plan and an intensity-modulated radiation therapy (IMRT) plan was then conducted. A clinical target volume (CTV), which encompassed a 1-mm margin along the distal 2 cm of the catheter, was delineated for both plans. Given positioning uncertainty under image guidance, a planning target volume (PTV = CTV + 3-mm margin) was defined for the IMRT plan. The IMRT plan was optimized for maximal CTV coverage but subsequently normalized to the same CTV volume receiving 100% of the prescription dose (V100) of the brachytherapy plan.
  
  
  
  The IMRT plan was normalized to the brachytherapy CTV V100of 82.0%. The PTV V100of this plan was 34.1%. The PTV exhibited dosimetric undercoverage within the middle ear and toward the external ear. Mean cochlea doses for the IMRT and brachytherapy plans were 26.7% and 10.5% of prescription, respectively.
  
  
  
  For rhabdomyosarcomas limited to the EAC, a standard brachytherapy catheter can deliver a highly conformal radiation plan that can spare the nearby cochlea from excess radiation.
authors.affiliation: Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY.
authors.forename: Martin T
authors.initials: MT
authors.lastname: King
authors.affiliation: Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY.
authors.forename: Laszlo
authors.initials: L
authors.lastname: Voros
authors.affiliation: Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY.
authors.forename: Gil'ad N
authors.initials: GN
authors.lastname: Cohen
authors.affiliation: Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY.
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Lanning
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Memorial Sloan-Kettering Cancer Center, New York, NY.
authors.forename: Ian
authors.initials: I
authors.lastname: Ganly
authors.affiliation: Department of Pediatrics, West Virginia University School of Medicine, Charleston, WV.
authors.forename: Chibuzo C
authors.initials: CC
authors.lastname: O'Suoji
authors.affiliation: Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY. Electronic address: woldens@mskcc.org.
authors.forename: Suzanne L
authors.initials: SL
authors.lastname: Wolden
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D003051:Cochlea / Q000000981:diagnostic imaging; D004424:Ear Canal; D004428:Ear Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D007223:Infant; D058958:Organs at Risk / Q000000981:diagnostic imaging; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D018233:Rhabdomyosarcoma, Embryonal / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D014057:Tomography, X-Ray Computed
keywords: External auditory canal; High-dose rate; Pediatrics; Rhabdomyosarcoma