Monte carlo simulation of surface percent depth dose

[[abstract]]©2002 Elsevier - This work studied the surface percent depth dose of 6 and 15 MV X-rays. 10 x 10 cm(2) and 20 x 20 cm(2) fields by Monte Carlo simulation. The OMEGA/BEAM code, an EGS4 user code developed by the NRCC, was used. The linac, Siemens PRIMUS, was accurately modeled according to the ion chamber and CEA film measurement, and the phase space data generated from this linac were collected to simulate dose distribution in water. The water phantom had radius 30cm and thickness 10cm. The percent depth doses at zero depth. PDDsurfaces for 6MV X-rays were 13.85 +/- 0.11% and 23.21 +/- 0.20% for the 10 x 10cm(2) and 20 x 20cm(2) fields. respectively. For 15MV X-rays, PDDsurface values were 8.83 +/- 0.07% and 18.60 +/- 0.12% for the 10 x 10cm(2) and 20 x 20cm(2) fields, respectively.[[department]]生醫工程與環境科學