Özet:

OBJECTIVES To examine the effect of thermoplastic masks used for immobilization on surface dose at Co-60 and 6MV photon energies. METHODS Three pieces of Aquaplast masks were used. One of these masks was used intact as a standard. The hole diameters of the other masks were stretched 1.25 and 2-fold. The masks were numbered as 1, 2, 3. Doses were measured with Markus parallel-plate (pp) ionization chamber, EBT2 film and MOSFET dosimetry. RESULTS The 1, 2 and 3 numbered masks were increased the surface dose from 24.2% to %73.3, 55.6% and %40.6, respectively, for 10x10 cm2 at Co-60. For 6MV, the surface dose of 14.4% increased to 50.1%, 34.7% and 23.7%, respectively. Markus pp results were compatible with the EBT2 film results. MOSFET measured higher surface doses. CONCLUSION The surface dose increases in the presence of mask. Mask material thickness and hole diameter significantly affects the surface dose. The diameter of the holes should be enlarged or cut the relevant region.

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