CAJ | 학술논문

Background and Objective: The planning dose distribution of intensity-modulated radiation therapy (IMRT) has to be verified before clinical implementation. The commonly used verification method is to measure the beam fluency at 0 degree (0°) gantry angle with a 2-dimensional (2D) detector array, but not the composite dose distribution of the real delivery in the planned gantry angles. This study was to investigate the angular dependence of a 2D diode array (2D array) and the feasibility of using it to verify the composite dose distribution of IMRT. Methods: Angular response of the central detector in the 2D array was measured for 6 MV X-ray, 10 cm × 10 cm field and 100 cm source axis distance (SAD) in different depths. With the beam incidence angle of 0°-60°, at intervals of 10°, and inherent buildup of the 2D array (2 g/cm2), the array was Irradiated and the readings of the central diode were compared with the measurement of thimble ionization chamber. Using a combined 30cm×30cm×30cm phantom which consisted of solid water slabs on top and underlying the 2D array, with the diode detectors placed at 8 g/cm2 depth, measurements were taken for beam angles of 0°-180° at intervals of 10° and compared with the calculation of treatment planning system (TPS) that pre-verified with ion chamber measuring. Results: Differences between the array detector and thimble chamber measurements were greater than 1% and 3.5% when the beam angle was larger than 30° and 60°, respectively. The measurements in the combined phantom were different from the calculation as high as 20% for 90° beam angle, 2% at 90°± 5° and less than 1% for all the other beam angles. Conclusions: The 2D diode array is capable of being used in composite dose verification of IMRT when the beam angles of 90°±5° and 270°± 5° are avoided.