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Electron contamination due to Lucite in a 45-MV photon beam

Journal Article · · Med. Phys.; (United States)
DOI:https://doi.org/10.1118/1.595523· OSTI ID:5930105
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The presence of the Lucite blocking tray in a 45-MV betatron beam leads to a considerable loss in the skin-sparing properties of this unit. Measurements conducted with a parallel-plate chamber show that the surface dose is approximately doubled (up to 58% of the maximum absorbed dose) and the depth of maximum dose is reduced by as much as 1.5 cm by the Lucite. These results suggest that separate dosimetry data should be kept for blocked and unblocked fields. The penetration of the electron contamination to the open field depth of maximum dose can lead to erroneous results if attenuation measurements are made at that depth. Studies of the effect of the lead sheet and leaded acrylic on the surface dose showed that under normal circumstances the presence of high-Z materials increases the surface dose, hence these materials cannot in general be used as electron filters on very high energy x-ray units. A Luciteless blocking tray with universal triangular corner blocks has been designed for use in special cases requiring a reduced surface dose.

Research Organization:
Tufts-New England Medical Center, Boston, MA
OSTI ID:
5930105
Journal Information:
Med. Phys.; (United States), Journal Name: Med. Phys.; (United States) Vol. 11:4; ISSN MPHYA
Country of Publication:
United States
Language:
English

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Related Subjects

550603 -- Medicine-- External Radiation in Therapy-- (1980-)
560151* -- Radiation Effects on Animals-- Man
62 RADIOLOGY AND NUCLEAR MEDICINE
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
ATTENUATION
BEAMS
BIOLOGICAL SHIELDING
BODY
DEPTH DOSE DISTRIBUTIONS
DOSES
DOSIMETRY
ELECTRONS
ELEMENTARY PARTICLES
ENERGY LOSSES
ESTERS
FERMIONS
LEPTONS
LOSSES
LUCITE
MATERIALS
MEDICINE
NUCLEAR MEDICINE
ORGANIC COMPOUNDS
ORGANIC POLYMERS
ORGANS
PETROCHEMICALS
PETROLEUM PRODUCTS
PHOTON BEAMS
PLASTICS
POLYACRYLATES
POLYMERS
POLYVINYLS
RADIATION DOSE DISTRIBUTIONS
RADIATION DOSES
RADIOLOGY
RADIOTHERAPY
SHIELDING
SKIN
SPATIAL DOSE DISTRIBUTIONS
SYNTHETIC MATERIALS
THERAPY