Evaluation of plastic materials for range shifting, range compensation, and solid-phantom dosimetry in carbon-ion radiotherapy

Journal Article · Mon Apr 15 00:00:00 EDT 2013 · Medical Physics

DOI:https://doi.org/10.1118/1.4795338· OSTI ID:22130587

Kanematsu, Nobuyuki; Koba, Yusuke; Ogata, Risa ^[1]

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1. Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555 (Japan)

Purpose: Beam range control is the essence of radiotherapy with heavy charged particles. In conventional broad-beam delivery, fine range adjustment is achieved by insertion of range shifting and compensating materials. In dosimetry, solid phantoms are often used for convenience. These materials should ideally be equivalent to water. In this study, the authors evaluated dosimetric water equivalence of four common plastics, high-density polyethylene (HDPE), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), and polyoxymethylene (POM). Methods: Using the Bethe formula for energy loss, the Gottschalk formula for multiple scattering, and the Sihver formula for nuclear interactions, the authors calculated the effective densities of the plastics for these interactions. The authors experimentally measured variation of the Bragg peak of carbon-ion beams by insertion of HDPE, PMMA, and POM, which were compared with analytical model calculations. Results: The theoretical calculation resulted in slightly reduced multiple scattering and severely increased nuclear interactions for HDPE, compared to water and the other plastics. The increase in attenuation of carbon ions for 20-cm range shift was experimentally measured to be 8.9% for HDPE, 2.5% for PMMA, and 0.0% for POM while PET was theoretically estimated to be in between PMMA and POM. The agreement between the measurements and the calculations was about 1% or better. Conclusions: For carbon-ion beams, POM was dosimetrically indistinguishable from water and the best of the plastics examined in this study. The poorest was HDPE, which would reduce the Bragg peak by 0.45% per cm range shift, although with marginal superiority for reduced multiple scattering. Between the two clear plastics, PET would be superior to PMMA in dosimetric water equivalence.

• OSTI ID: 22130587
• Journal Information: Medical Physics, Vol. 40, Issue 4; Other Information: (c) 2013 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-2405
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
61 RADIATION PROTECTION AND DOSIMETRY
62 RADIOLOGY AND NUCLEAR MEDICINE
36 MATERIALS SCIENCE
CARBON IONS
COMPARATIVE EVALUATIONS
CONTROL
DENSITY
DOSIMETRY
ENERGY LOSSES
HEAVY IONS
INTERACTIONS
MULTIPLE SCATTERING
PEAKS
PHANTOMS
PLASTICS
PMMA
POLYETHYLENES
RADIOACTIVE ION BEAMS
RADIOTHERAPY
SOLIDS
WATER