A Comparative Study and Dose Evaluation of Photon Beam for water phantom, 2D-array and Treatment Planning System in Small Field Sizes

This study assessed the clinical usefulness of the 2D-Array Seven29 by comparing the dose of Photon Beam for water phantom, 2D-array and Treatment Planning System in five Field sizes. The experimental equipment included the linear accelerator, treatment planning system (TPS), water phantom, 2D-Array, solid phantoms, and two types of ionization chambers (Semiflex and Pinpoint). The distance between the ray source and the center of the ion chamber was fixed to SSD of 100 cm during the experiment. The field size was 10 x 10 cm(2) and the radiation energies of the photon beam were 6 MV and 15 MV. The energy fields sizes involved (1x1, 2x2, 3x3, 4x4, 5x5,). The relative deviation ratio of the TPS in water phantom and TPS to 2darray in the solid phantom was calculated. The measured doses in standard phantom were lower than TPS values for small field dimensions (less than 3x3 cm(2)). The data measured by 2D-Array for fields 2x2 and 3x3cm(2) within +/- 2% indicated a good accuracy of measurement planning system for field size 1 x 1cm(2) . The measured doses in the standard phantom was lower than the TPS values for small field dimensions and the data measured by 2D-Array for 6 MV shows mild differences between the TPS and the experimental data. A slight difference appeared between the TPS and the experimental data using 2D-Array for 15 MV. The results were the same for the TPS and the measured data, at only a field dimension of 1 x 1cm(2). The measured data increased as field area enlarged from 2x2 to 5x5cm(2) by a constant value of 4%.