title: The relevance of dosimetry in animal models of cochlear irradiation.
abstract: OBJECTIVE
  To compare dose measurements of three different irradiation setups for an animal model of unilateral cochlear irradiation using radiochromic films positioned at the cochlear plane. A method of dosimetry is proposed.
  
  
  METHODS
  Radiation field simulation was performed to locate the cochlear plane for irradiation experiments using CT scan images. Fifteen film pieces were irradiated at the cochlear plane with 3 different irradiation field sizes. A 12-mm diameter field (n = 5), 5.7 mm diameter field (n = 5), and a 6.5 × 7.2 mm field (n = 5). After obtaining an ideal irradiation field size, 15 film pieces were used to compare dosimetry between tissue substitute materials (PVC n = 5 and PVC + Teflon, 5 each) and real tissue (frozen animal, n = 5). Auditory brainstem responses at 3 frequencies (8, 16, 20, and 25 kHz) were performed on 7 guinea pigs after a cycle of fractionated unilateral irradiation.
  
  
  RESULTS
  Dosimetry in real tissue demonstrated an asymmetric dose distribution at the cochlear plane and ultimately a lower dose deposition (30%) when compared with tissue substitute materials. Auditory brainstem responses of ears subjected to radiotherapy demonstrated progressive hearing loss in long-term assessment.
  
  
  CONCLUSIONS
  Asymmetric dose deposition at the cochlear plane highlights the need of comprehensive real tissue dosimetry in animal studies of cochlear irradiation. To avoid misleading discrepancies in dose-deposition between different studies using the same animal model, appropriate planning and confirmatory dosimetry systems are highly desirable.
authors.affiliation: *McGill Auditory Sciences Laboratory; †Medical Physics Unit, McGill University; ‡Department of Radiation Oncology, Jewish General Hospital; and §Department of Otolaryngology, The Montreal Children's Hospital, Montréal, QC, Canada.
authors.forename: Mario A
authors.initials: MA
authors.lastname: Mujica-Mota
authors.forename: Slobodan
authors.initials: S
authors.lastname: Devic
authors.forename: Sam J
authors.initials: SJ
authors.lastname: Daniel
mesh_terms: D000818:Animals; D001309:Auditory Threshold / Q000528:radiation effects; D003051:Cochlea / Q000528:radiation effects*; D016057:Evoked Potentials, Auditory, Brain Stem / Q000528:radiation effects; D005260:Female; D007839:Functional Laterality; D006168:Guinea Pigs; D008954:Models, Biological; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D014057:Tomography, X-Ray Computed