Angular dependence investigation of the MatriXX detector array for dosimetric verification of treatment plans with intensity modulation

The angular sensitivity of the MatriXX ionizing chambers array (IBA Dosimetry) was investigated in order to make corrections to the measured dose distribution with the aim of the accuracy improvement of intensity modulated plans verification. MatriXX in combination with the phantom was irradiated using medical linear accelerator at various gantry positions. The measured dose distribution for each irradiated angle was processed in Python3 and compared with the reference calculated one. The reference dose distribution for the corresponding geometry was obtained using the calculation in the planning system Monaco 5.10 (Elekta). Sets of correction coefficients for the angular sensitivity of the MatriXX detector array as a function of the accelerator gantry angle have been created. The angular dependence of MatriXX was analyzed statistically, after which it was decided to use a single correction factor for each row of detectors, except for angles in the ranges $90^\circ{-}95^\circ$ and~$265^\circ{-}270^\circ$, where a unique factor was applied for each detector. The use of the developed correction factors that take into account the angular sensitivity of the detectors made it possible to increase the measurement accuracy and thereby obtain better dosimetric verification results, in comparison with the measurements where the angular sensitivity was not taken into account.