The validity of the density scaling method in primary electron transport for photon and electron beams

Journal Article · Thu Mar 01 00:00:00 EST 1990 · Medical Physics; (USA)

DOI:https://doi.org/10.1118/1.596497· OSTI ID:6826973

Woo, M K; Cunningham, J R ^[1]

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1. Department of Medical Biophysics, University of Toronto, Toronto, Canada M4X 1K9 (CA)

In the convolution/superposition method of photon beam dose calculations, inhomogeneities are usually handled by using some form of scaling involving the relative electron densities of the inhomogeneities. In this paper the accuracy of density scaling as applied to primary electrons generated in photon interactions is examined. Monte Carlo calculations are compared with density scaling calculations for air and cork slab inhomogeneities. For individual primary photon kernels as well as for photon interactions restricted to a thin layer, the results can differ significantly, by up to 50%, between the two calculations. However, for realistic photon beams where interactions occur throughout the whole irradiated volume, the discrepancies are much less severe. The discrepancies for the kernel calculation are attributed to the scattering characteristics of the electrons and the consequent oversimplified modeling used in the density scaling method. A technique called the kernel integration technique is developed to analyze the general effects of air and cork inhomogeneities. It is shown that the discrepancies become significant only under rather extreme conditions, such as immediately beyond the surface after a large air gap. In electron beams all the primary electrons originate from the surface of the phantom and the errors caused by simple density scaling can be much more significant. Various aspects relating to the accuracy of density scaling for air and cork slab inhomogeneities are discussed.

• OSTI ID: 6826973
• Journal Information: Medical Physics; (USA), Vol. 17:2; ISSN 0094-2405
• Country of Publication: United States
• Language: English

Related Subjects

61 RADIATION PROTECTION AND DOSIMETRY
ELECTRON DOSIMETRY
RADIATION TRANSPORT
PHANTOMS
RADIATION DOSE DISTRIBUTIONS
X-RAY DOSIMETRY
AIR
CORK
ELECTRON BEAMS
KERNELS
PHOTON BEAMS
SCALING
BEAMS
DOSIMETRY
FLUIDS
GASES
LEPTON BEAMS
MOCKUP
PARTICLE BEAMS
STRUCTURAL MODELS
655003* - Medical Physics- Dosimetry