Dosimetry for Intensity Modulated Radiotherapy (IMRT) Technique Using Ion Chamber Matrix (MatriXX-FFF) with Back Projection Method (Usual 6MV and 10MV)

Dose verification needs to be carried out on pre-treatment to get dose characteristics when using Intensity Modulated Radiotherapy (IMRT) technique. One of the dosimetry tools is 2D-array of the ionization chamber detectors which gives the measurement result in real-time, and does not require periodic calibration. However, this dosimetry tool has limited spatial resolution, it depends on the size and shape of the detector, and its result is affected by secondary electron transport from the detector wall to detector volume. These factors may lead to low verification result (gamma parameter). One technique to overcome these problems is using back-projection method. In this study, the kernel function was obtained from a square field of 4 cm by deconvolution from the comparison of MatriXX-FFF and TPS. The obtained kernel was then applied using convolution with variations of a square field, no-Build-Up and Build-Up condition, and IMRT parameter. The analysis of the gamma parameter was used to analyse the effectiveness of this method. The analysis results showed the increasing of passing grade value for all fields (0 % - 15.9 %, μ = 4.84%, σ = 4.81 %), with the highest was on some square fields, such as 4 cm and 5 cm. This indicated the dependence of kernel function to the size of the field. Moreover, the result of applying IMRT to certain case led to the increase of passing grade values.