Dose buildup for obliquely incident photon beams

Journal Article · Fri May 01 04:00:00 EDT 1987 · Med. Phys.; (United States)

DOI:https://doi.org/10.1118/1.596055· OSTI ID:6780163

Gerbi, B J; Meigooni, A S; Khan, F M

For obliquely incident photon beams, the buildup of dose with depth is markedly different from normally incident beams. However, relatively little data on this topic exists for high-energy photon beams of energy greater than 6 MV. Measurements of dose in the buildup region were made using a plane-parallel ionization chamber in a polystyrene phantom with obliquely incident 6-, 10-, 18-, and 24-MV x-ray beams angled 0/sup 0/ to 84/sup 0/. Buildup curves at these angles were plotted and from these an obliquity factor, defined as the ratio of ionization charge collected at a point for a particular angle of incidence to that collected at the same point at normal incidence, was determined. For each energy, the obliquity factor as a function of depth, field size, and source--chamber distance was studied. Results indicate that the obliquity factor is highly dependent on the beam energy, angle of incidence, the collimator opening, and the source--skin distance. A mathematical expression has been developed to predict the dose in the buildup region of high-energy photon beams for various angles of beam incidence, field size, and chamber distance.

• Research Organization: Department of Therapeutic Radiology, University of Minnesota Hospital and Clinic, Minneapolis, Minnesota 55455
• OSTI ID: 6780163
• Journal Information: Med. Phys.; (United States), Journal Name: Med. Phys.; (United States) Vol. 14:3; ISSN MPHYA
• Country of Publication: United States
• Language: English

Related Subjects

61 RADIATION PROTECTION AND DOSIMETRY
655003* -- Medical Physics-- Dosimetry
BEAMS
BUILDUP
DEPTH DOSE DISTRIBUTIONS
DOSIMETRY
MATERIALS
MEDICINE
MOCKUP
NUCLEAR MEDICINE
ORGANIC COMPOUNDS
ORGANIC POLYMERS
PETROCHEMICALS
PETROLEUM PRODUCTS
PHANTOMS
PHOTON BEAMS
PLASTICS
POLYMERS
POLYOLEFINS
POLYSTYRENE
POLYVINYLS
RADIATION DOSE DISTRIBUTIONS
RADIOLOGY
RADIOTHERAPY
SPATIAL DOSE DISTRIBUTIONS
STRUCTURAL MODELS
SYNTHETIC MATERIALS
THERAPY
X-RAY DOSIMETRY