Depth dependence determination of the wedge transmission factor for 4--10 MV photon beams

Journal Article · Fri Jul 01 00:00:00 EDT 1988 · Med. Phys.; (United States)

DOI:https://doi.org/10.1118/1.596216· OSTI ID:6988797

McCullough, E C; Gortney, J; Blackwell, C R

The depth dependence (up to 25 cm) of the in-phantom wedge transmission factor (WTF) has been determined for three medical linear accelerator x-ray beams with energies of 4, 6, and 10 MV containing 15/sup 0/--60/sup 0/ (nominal) brass wedges. All measurements were made with a cylindrical ionization chamber in water, for a field size of 10 x 10 cm/sup 2/ with a source--skin distance of 80 or 100 cm. We conclude that, for the accelerators studied, the WTF factor at depth is less than 2% different from that determined at d/sub max/ (for the nominal wedge angles and photon energies studied) unless the depth of interest is greater than 10 cm. Up to the maximum depth studied (25 cm) the relative wedge factor: that is, wedge factor at depth compared to that determined at d/sub max/ : was about equal to or less than 1.02 for the 15/sup 0/ and 30/sup 0/ wedges and any of the photon beam energies studied. For the seldom utilized combination of a nominal wedge angle in excess of 45/sup 0/ with a depth greater than 10 cm, the WTF at depth can differ from the WTF determined at d/sub max/, by up to 5%. Since the wedge transmission factor is reflective of relative percent dose data, our results also indicate that it is in error to use open field percent depth doses for certain combinations of wedge angle, photon energy, and depth.

• Research Organization: Division of Radiation Oncology, Mayo Clinic/Foundation, Rochester, Minnesota 55905
• OSTI ID: 6988797
• Journal Information: Med. Phys.; (United States), Vol. 15:4
• Country of Publication: United States
• Language: English

Related Subjects

61 RADIATION PROTECTION AND DOSIMETRY
X-RAY DOSIMETRY
DEPTH DOSE DISTRIBUTIONS
LINEAR ACCELERATORS
PHANTOMS
PHOTON BEAMS
RADIATION SOURCES
RADIOTHERAPY
WATER
ACCELERATORS
BEAMS
DOSIMETRY
HYDROGEN COMPOUNDS
MEDICINE
MOCKUP
NUCLEAR MEDICINE
OXYGEN COMPOUNDS
RADIATION DOSE DISTRIBUTIONS
RADIOLOGY
SPATIAL DOSE DISTRIBUTIONS
STRUCTURAL MODELS
THERAPY
655003* - Medical Physics- Dosimetry