Radiological properties of a wax-gypsum compensator material.
In this paper the radiological properties of a compensator material consisting of wax and gypsum is presented. Effective attenuation coefficients (EACs) have been determined from transmission measurements with an ion chamber in a Perspex phantom. Measurements were made at 80 and 100 cm source-to-skin distance (SSD) for beam energies of 6, 8, and 15 MV, for field sizes ranging from narrow beam geometries up to 40 x 40 cm2, and at measurement depths of maximum dose build-up, 5 and 10 cm. A parametrization equation could be constructed to predict the EAC values within 4% uncertainty as a function of field size and depth of measurement. The EAC dependence on off-axis position was also quantified at each beam energy and SSD. It was found that the compensator material reduced the required thickness for compensation by 26% at 8 MV when compared to pure paraffin wax for a 10 x 10 cm2 field. Relative surface ionization (RSI) measurements have been made to quantify the effect of scattered electrons from the wax-gypsum compensator. Results indicated that for 80 cm SSD the RSI would exceed 50% for fields larger than 15 x 15 cm2. At 100 cm SSD the RSI values were below 50% for all field sizes used.
Medical Physics Department, Faculty of Health Sciences, University of the Free State, PO. Box 339, Bloemfontein, 9300 South Africa. Freek.duplessis@fccc.edu
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D002133:Calcium Sulfate / Q000737:chemistry* / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D018499:Linear Energy Transfer; D008422:Materials Testing / Q000379:methods; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D011878:Radiotherapy / Q000295:instrumentation* / Q000379:methods*; D012542:Scattering, Radiation; D014885:Waxes / Q000737:chemistry* / Q000528:radiation effects*
D014885:Waxes; D002133:Calcium Sulfate