Measurement and properties of the dose–area product ratio in external small-beam radiotherapy

In small-beam radiation therapy (RT) the measurement of the beam quality parameter, i.e. the tissue–phantom ratio or TPR 20,10 , using a conventional point detector is a challenge. To obtain reliable results, one has to consider potential sources of error, including volume averaging and adjustment of the point detector into the narrow beam. To overcome these challenges, a different type of beam quality parameter in small beams was studied, namely the dose–area product ratio, or DAPR 20,10 . With this method, the measurement of a dose–area product (DAP) using a large-area plane-parallel chamber (LAC) eliminates the uncertainties in detector positioning and volume averaging that are present when using a point detector. In this study, the properties of the DAPR 20,10 of a cone-collimated 6 MV photon beam were investigated using Monte Carlo (MC) calculations and the obtained values were compared to measurements obtained using two LAC detectors, PTW Type 3...

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