title: Proposed expansion margins for planning organ at risk volume for lenses during radiation therapy of the nasal cavity in dogs and cats.
abstract: Radiation therapy protocols for the feline or canine nasal cavity can damage epithelial cells of the posterior pole of the lens and lead to the development of cataracts. Aims of this retrospective, descriptive study were to calculate movements of the lens during radiation therapy of the nasal cavity in a sample of cats and dogs, and to propose species-specific expansion margins for planning organ at risk volume (PRV) to minimize radiation doses to the lens. All included patients were immobilized with an indexed bite block and positioned in a vacuum positioning cushion for head irradiation. On-board cone beam CT (CBCT) imaging was used for patient alignment. Both ocular lenses were contoured on the therapeutic CBCTs. Coregistration (fusion) between the planning CT and CBCTs was used to measure the movements of the lens. Two measurements were made: the differences between the centroid point of each lens as well as the displacement of the coregistrations. A total of 496 different observations were recorded from 14 cats and 52 dogs. Using the displacement results, we calculated how often the lens would be within the lens-PRV contour. We proposed that an optimal expansion margin from the lens volume of 2 mm in cats and 3 mm in dogs may be necessary in generating PRV expansion for the lens. From our results, we expect the lens would therefore be within these proposed PRV expansions in 92% of the feline measurements and 95% of the canine measurements.
authors.affiliation: Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, 4474, New Zealand.
authors.forename: Zaki
authors.initials: Z
authors.lastname: Jafry
authors.affiliation: Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, 4474, New Zealand.
authors.forename: Arnon
authors.identifier: http://orcid.org/0000-0002-6449-2812
authors.initials: A
authors.lastname: Gal
authors.affiliation: Department of Medical Physics, Grand River Regional Cancer Centre, Kitchener, ON, N2G 1G3, Canada.
authors.forename: Andre
authors.initials: A
authors.lastname: Fleck
authors.affiliation: Department of Medical Physics, Grand River Regional Cancer Centre, Kitchener, ON, N2G 1G3, Canada.
authors.forename: Johnson
authors.initials: J
authors.lastname: Darko
authors.affiliation: Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, 4474, New Zealand.|Animal Cancer Centre, Ontario Veterinary College, University of Guelph, Guelph, N1G 2W1, Ontario, Canada.
authors.forename: Valerie J
authors.initials: VJ
authors.lastname: Poirier
mesh_terms: D000818:Animals; D002371:Cat Diseases / Q000532:radiotherapy*; D002415:Cats; D054893:Cone-Beam Computed Tomography / Q000662:veterinary; D004283:Dog Diseases / Q000532:radiotherapy*; D004285:Dogs; D007908:Lens, Crystalline / Q000293:injuries* / Q000528:radiation effects; D009668:Nose Diseases / Q000532:radiotherapy / Q000662:veterinary*; D009929:Organ Size; D058958:Organs at Risk / Q000528:radiation effects*; D011832:Radiation Injuries / Q000517:prevention & control / Q000662:veterinary*; D012189:Retrospective Studies
keywords: CT scan; IGRT; IMRT; nasal tumor