title: Evaluation of underdosage in the external photon beam radiotherapy of glottic carcinoma: Monte Carlo study.
abstract: OBJECTIVE
  Underdosage in the human larynx may be the true factor behind the decrease in local control rates.
  
  
  METHODS
  To evaluate underdosage with Monte Carlo a CT-based geometrical model of the patient's neck (mathematical neck) was created. Dose was calculated for a pair of 6 Me V parallel-opposed photon beams modulated with 15 degree steel wedges.
  
  
  RESULTS
  At least 5% of volume of 3.5 cm(3) hypothetical tumor near the air wall of the larynx receives less than 86% of the maximum tumor dose. The same volume received less than 91% of the maximum tumor dose when the mathematical neck had no air cavities.
  
  
  CONCLUSIONS
  We conclude the significant underdosage at the air-tissue interface in the larynx occurs in traditional radiotherapy treatments, especially in the glottic part of the larynx.
authors.affiliation: Department of Radiation Oncology, Indiana University School of Medicine, Indianapolis, IN 46202-5289, USA. sspirydo@iupui.edu
authors.forename: Siarhei
authors.initials: S
authors.lastname: Spirydovich
authors.forename: Lech
authors.initials: L
authors.lastname: Papiez
authors.forename: Vadim
authors.initials: V
authors.lastname: Moskvin
authors.forename: Paul
authors.initials: P
authors.lastname: Desrosiers
mesh_terms: D019985:Benchmarking; D002277:Carcinoma / Q000532:radiotherapy*; D003198:Computer Simulation; D005931:Glottis / Q000528:radiation effects*; D006801:Humans; D021621:Imaging, Three-Dimensional; D007822:Laryngeal Neoplasms / Q000532:radiotherapy*; D008954:Models, Biological; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000706:statistics & numerical data*; D011882:Radiotherapy, High-Energy; D014057:Tomography, X-Ray Computed