An isodose shift technique for obliquely incident electron beams

Journal Article · Wed Nov 01 04:00:00 EST 1989 · Medical Physics; (USA)

DOI:https://doi.org/10.1118/1.596316· OSTI ID:5352759

Ulin, K; Sternick, E S ^[1]

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1. Medical Physics Division, Department of Radiation Oncology, Tufts-New England Medical Center, Boston, Massachusetts 02111 (US)

It is well known that when an electron beam is incident obliquely on the surface of a phantom, the depth dose curve measured normal to the surface is shifted toward the surface. Based on geometrical arguments alone, the depth of the {ital n}th isodose line for an electron beam incident at an angle {theta} should be equal to the product of cos {theta} and the depth of the {ital n}th isodose line at normal incidence. This method, however, ignores the effects of scatter and can lead to significant errors in isodose placement for beams at large angles of incidence. A semi-empirical functional relationship and a table of isodose shift factors have been developed with which one may easily calculate the depth of any isodose line for beams at incident angles of 0{degree} to 60{degree}. The isodose shift factors are tabulated in terms of beam energy (6--22 MeV) and isodose line (10%--90%) and are shown to be relatively independent of beam size and incident angle for angles {lt}60{degree}. Extensive measurements have been made on a Varian Clinac 2500 linear accelerator with a parallel-plate chamber and polystyrene phantom. The dependence of the chamber response on beam angulation has been checked, and the scaling factor of the polystyrene phantom has been determined to be equal to 1.00.

• OSTI ID: 5352759
• Journal Information: Medical Physics; (USA), Journal Name: Medical Physics; (USA) Vol. 16:6; ISSN 0094-2405; ISSN MPHYA
• Country of Publication: United States
• Language: English

Related Subjects

61 RADIATION PROTECTION AND DOSIMETRY
655003* -- Medical Physics-- Dosimetry
BEAMS
DEPTH DOSE DISTRIBUTIONS
DOSIMETRY
ELECTRON BEAMS
ELECTRON DOSIMETRY
ELECTRONS
ELEMENTARY PARTICLES
ENERGY RANGE
FERMIONS
INCIDENCE ANGLE
ISODOSE CURVES
LEPTON BEAMS
LEPTONS
MATERIALS
MEDICINE
MEV RANGE
MEV RANGE 01-10
MEV RANGE 10-100
MOCKUP
NUCLEAR MEDICINE
ORGANIC COMPOUNDS
ORGANIC POLYMERS
PARTICLE BEAMS
PETROCHEMICALS
PETROLEUM PRODUCTS
PHANTOMS
PLASTICS
POLYMERS
POLYOLEFINS
POLYSTYRENE
POLYVINYLS
RADIATION DOSE DISTRIBUTIONS
RADIOLOGY
RADIOTHERAPY
SPATIAL DOSE DISTRIBUTIONS
STRUCTURAL MODELS
SYNTHETIC MATERIALS
THERAPY