Surface Dose Measurements on an Indigenously Made Inhomogeneous Female Pelvic Phantom Using Metal-Oxide-Semiconductor-Field-Effect-Transistor Based Dosimetric System

Introduction: Megavoltage X-ray beams are used to treat cervix cancer due to their skin-sparing effect. Preferably, the radiation surface doses should be negligible; however, it increases due to electron contamination produced by various field parameters. Therefore, it is essential to provide proper knowledge about the effect of different field parameters on radiation doses. This study sought to find out the effect of various physical parameters on the surface doses. Materials and Methods: The effects of field size, source-to-surface distance, and open or acrylic block tray fields on surface doses were determined.  Metal-Oxide-Semiconductor-Field-Effect-Transistor based dosimetric system was used for dose measurements for 6 MV photon beam. The directly measured radiation surface doses on pelvic phantom were compared to surface dose values computed by treatment planning system in the similar field parameters. Results: The measured results for the percentage depth dose (PDD0) in field size of 10x10 cm2  were 13.32%, 12.95% and 13.87% for open field and 36.87%, 36.31% and 35.88%  for acrylic block tray field. In addition, the computed doses were 7.83%, 7.73% and 7.65% for open field and 16.33%, 16.12% and 15.88% for acrylic block tray field at 80 cm, 100 cm, and 120 cm SSDs, respectively. Conclusion: The surface dose increases along with the size of the field and decreases with increasing SSD. The surface doses in acrylic block tray fields were significantly higher than the open ones. The treatment planning system computed a lesser radiation doses in same field parameters. 

Keywords:

Surface Dose , Phantoms , MOSFET Dosimetry , Treatment Planning System