Buildup/surface dose and exit dose measurements for a 6-MV linear accelerator

Journal Article · Sat Mar 01 04:00:00 EST 1986 · Med. Phys.; (United States)

DOI:https://doi.org/10.1118/1.595908· OSTI ID:5924067

Purdy, J A

The central axis dose distribution in the buildup region for the Varian Clinac 6/100 6-MV x-ray beam was measured in a polystyrene phantom using a fixed volume (0.5 cm/sup 3/) parallel-plate ionization chamber (2.4-mm plate separation). Results for the surface dose measurements ranged from approximately 8% of the maximum dose for a 5 x 5 cm field, up to 36% for a 40 x 40 cm field, 100-cm source--skin distance. The effect of a 0.6-cm-thick polycarbonate blocking tray and metal filters on the surface and buildup dose is also reported. In addition, ionization measurements were made to document the dose perturbations caused by the absence of backscattering material at the exit surface of a polystyrene phantom. Exit dose measurements showed a 15% reduction in dose with essentially no scattering material beyond the measurement point. Near full scatter condition could be restored by placing 5--10 mm (depending on field size) of unit density material directly behind the ion chamber's distal surface.

• Research Organization: Washington University School of Medicine, Mallinckrodt Institute of Radiology, St. Louis, Missouri 63110
• OSTI ID: 5924067
• Journal Information: Med. Phys.; (United States), Journal Name: Med. Phys.; (United States) Vol. 13:2; ISSN MPHYA
• Country of Publication: United States
• Language: English

Related Subjects

61 RADIATION PROTECTION AND DOSIMETRY
655003* -- Medical Physics-- Dosimetry
ACCELERATORS
BUILDUP
DOSIMETRY
IONIZATION
LINEAR ACCELERATORS
MOCKUP
PHANTOMS
RADIATION DOSE DISTRIBUTIONS
STRUCTURAL MODELS
X-RAY DOSIMETRY