title: Dosimetric comparison between three dimensional treatment planning system, Monte Carlo simulation and gel dosimetry in nasopharynx phantom for high dose rate brachytherapy.
abstract: OBJECTIVE
  For the treatment of nasopharnx carcinoma (NPC) using brachytherapy methods and high-energy photon sources are common techniques. In the common three dimensional (3D) treatments planning, all of the computed tomography images are assumed homogeneous. This study presents the results of Monte Carlo calculations for non-homogeneous nasopharynx phantom, MAGICA normoxic gel dosimetry and 3D treatment planning system (TPS).
  
  
  METHODS
  The head phantom was designed with Plexiglas cylinder, head bone, and nasopharynx brachytherapy silicon applicator. For the simulations, version 5 of the Monte Carlo N-particle transport code (MCNP5) was used. 3D treatment planning was performed in Flexiplan software. A normoxic radiosensitive polymer gel was fabricated under normal atmospheric conditions and poured into test tubes (for calibration curve) and the head phantom. In addition, the head phantom was irradiated with Flexitron afterloader brachytherapy machine with (192)Ir source. To obtain calibration curves, 11 dosimeters were irradiated with dose range of 0-2000 cGy. Evaluations of dosimeters were performed on 1.5T scanner.
  
  
  RESULTS
  Two-dimensional iso-dose in coronal plan at distances of z = +0.3, -0.3 cm was calculated. There was a good accordance between 3D TPS and MCNP5 simulation and differences in various distances were between 2.4% and 6.1%. There was a predictable accordance between MAGICA gel dosimetry and MCNP5 simulation and differences in various distances were between 5.7% and 7.4%. Moreover, there was an acceptable accordance between MAGICA gel dosimetry and MCNP5 data and differences in various distances were between 5.2% and 9.4%.
  
  
  CONCLUSIONS
  The sources of differences in this comparison are divided to calculations variation and practical errors that was added in experimental dosimetry. The result of quality assurance of nasopharynx high dose rate brachytherapy is consistent with international standards.
authors.affiliation: Agricultural, Medical and Industrial Research School, Nuclear Science and Technology Research Institute, Karaj, Iran.
authors.forename: Zeynab
authors.initials: Z
authors.lastname: Fazli
authors.forename: Mahdi
authors.initials: M
authors.lastname: Sadeghi
authors.forename: M H
authors.initials: MH
authors.lastname: Zahmatkesh
authors.forename: Seied Rabei
authors.initials: SR
authors.lastname: Mahdavi
authors.forename: Claudio
authors.initials: C
authors.lastname: Tenreiro
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods* / Q000592:standards*; D002277:Carcinoma; D003198:Computer Simulation; D006801:Humans; D008279:Magnetic Resonance Imaging; D009010:Monte Carlo Method; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D019047:Phantoms, Imaging; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted