Correlation Between Detector Array Measurements and a Computer Algorithm for Enhanced Dynamic Wedge Profiles

Abstract 

Verification of dosimetric data computed by a treatment planning system is necessary in the commissioning process for any clinical software, just as it is necessary for any annual quality assurance testing. Direct verification of the dosimetric data is achievable when calculating the enhanced dynamic wedge (EDW) off-axis ratio at each point of interest. As mathematical models for hand-calculating such factors are still evolving, measurement of these external beam arrangements has proven significantly more accurate. This research presents a correlation for measured and planned data, specific for 6- and 18-MV photon beams on a Varian 21EX linear accelerator, using the EDW mode. Field generation was created using the Varian Eclipse treatment planning system. On treatment field delivery, the Sun Nuclear MapCHECK diode array was used to plot each beam profile in 2 dimensions. Wedge angles of 10°, 15°, 20°, 25°, 30°, 45° and 60° were studied here, under isocentric geometry, at a fixed water equivalent depth of 15 cm. Field size dependence was considered with each wedge and energy combination, where symmetric apertures of 5 × 5 cm², 10 × 10 cm², 15 × 15 cm² and 20 × 20 cm² were used. Accurate dosimetric results were found to be achievable when using this treatment planning system to within 2.8% maximum deviation, and to within 1% deviation averaged over all. The diode array also proved to be simple and ideally suited for EDW measurements.

Key Words: Diode, Eclipse, EDW, MapCHECK