Determination of correction factors for a 2D diode array device in MV photon beams
Abstract
The purpose of this study is to evaluate the dosimetric characteristics of a 2D diode array device (MAPCHECK) and provide correction factors for clinically relevant conditions. Measurements were performed for various collimator settings (5 x 5-40 x 40 cm2), SSDs (80-110 cm), and depths (5-20 cm) for 6 and 15 MV photon beams. The correction factor was determined as the ratio of dose measured by an ionization chamber in a large full scatter water phantom to the dose measured by the MAPCHECK with 30 x 30 cm2 solid water phantom. The total correction factor was separated into three components. The phantom scatter factor was evaluated by taking the ratio of dose measured by MAPCHECK with backscatter material and 30 x 30 cm2 phantom to that by the ionization chamber in an infinite large water phantom renormalized to the reference field size (10 x 10 cm2). This was also compared to the theoretical calculation using ratios of phantom scatter factor between an infinitely large water phantom and 30 x 30 cm2 solid water phantoms. The backscatter effect was determined by taking the ratio of the MAPCHECK measurements with and without 10 cm thick solid water backscatter material also normalized to the reference field size at the depth of measurement. The extra correction factor is defined as the ratio of dose measured by the MAPCHECK (without backscatter) to that measured by the ionization chamber in a large water phantom at depth d for the reference field size (10 x 10 cm2) normalized to…
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