title: Pencil beam scanning dosimetry for large animal irradiation.
abstract: The space radiation environment imposes increased dangers of exposure to ionizing radiation, particularly during a solar particle event. These events consist primarily of low-energy protons that produce a highly inhomogeneous depth-dose distribution. Here we describe a novel technique that uses pencil beam scanning at extended source-to-surface distances and range shifter (RS) to provide robust but easily modifiable delivery of simulated solar particle event radiation to large animals. Thorough characterization of spot profiles as a function of energy, distance and RS position is critical to accurate treatment planning. At 105 MeV, the spot sigma is 234 mm at 4800 mm from the isocentre when the RS is installed at the nozzle. With the energy increased to 220 MeV, the spot sigma is 66 mm. At a distance of 1200 mm from the isocentre, the Gaussian sigma is 68 mm and 23 mm at 105 MeV and 220 MeV, respectively, when the RS is located on the nozzle. At lower energies, the spot sigma exhibits large differences as a function of distance and RS position. Scan areas of 1400 mm (superior-inferior) by 940 mm (anterior-posterior) and 580 mm by 320 mm are achieved at the extended distances of 4800 mm and 1200 mm, respectively, with dose inhomogeneity <2%. To treat large animals with a more sophisticated dose distribution, spot size can be reduced by placing the RS closer than 70 mm to the surface of the animals, producing spot sigmas below 6 mm.
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, 3400 Civic Center Blvd, 2326 TRC, PCAM, Philadelphia, PA 19104, USA linl@uphs.upenn.edu.
authors.forename: Liyong
authors.initials: L
authors.lastname: Lin
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, 3400 Civic Center Blvd, 2326 TRC, PCAM, Philadelphia, PA 19104, USA.
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Solberg
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, 3400 Civic Center Blvd, 2326 TRC, PCAM, Philadelphia, PA 19104, USA.
authors.forename: Alexandro
authors.initials: A
authors.lastname: Carabe
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, 3400 Civic Center Blvd, 2326 TRC, PCAM, Philadelphia, PA 19104, USA.
authors.forename: James E
authors.initials: JE
authors.lastname: Mcdonough
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, 3400 Civic Center Blvd, 2326 TRC, PCAM, Philadelphia, PA 19104, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Diffenderfer
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, 3400 Civic Center Blvd, 2326 TRC, PCAM, Philadelphia, PA 19104, USA.
authors.forename: Jenine K
authors.initials: JK
authors.lastname: Sanzari
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, 3400 Civic Center Blvd, 2326 TRC, PCAM, Philadelphia, PA 19104, USA.
authors.forename: Ann R
authors.initials: AR
authors.lastname: Kennedy
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, 3400 Civic Center Blvd, 2326 TRC, PCAM, Philadelphia, PA 19104, USA.
authors.forename: Keith
authors.initials: K
authors.lastname: Cengel
mesh_terms: D003359:Cosmic Radiation; D004583:Electrons; D004867:Equipment Design; D019544:Equipment Failure Analysis; D011522:Protons; D011829:Radiation Dosage; D011874:Radiometry / Q000295:instrumentation / Q000662:veterinary; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D012993:Solar Energy; D014916:Whole-Body Irradiation / Q000295:instrumentation / Q000662:veterinary; D013556:Swine, Miniature; D000818:Animals
chemical_list: D011522:Protons
keywords: large animal; pencil beam scanning; proton therapy; solar particle event; total body irradiation