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Effect of Surface Dose and Depth of Maximum Dose with Physical Wedge Filters for 6MV Flattened and 7MV Unflattened Photon Beams

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S Ashokkumar

S Ashokkumar*, S.N.Sinha, Girigesh Yadav, Kothanda Raman, Rajesh Thiyagarajan, Rajiv Gandhi Cancer Institute & Research Centre, New Delhi, India N Arunai Nambiraj,SAS , VIT University , Vellore , India

SU-E-T-151 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: To evaluate impact on surface dose, Depth of dose maximum (dmax) and depth dose distribution due to physical wedge filters for different wedge angle were studied for 6MV flattened (6MV FB) and 7MV unflattened (7MV UFB) photon beams.

Methods: The flattening filter and primary collimator are the major sources of producing the scattered radiation and these parameters affect the surface dose, dmax and dose distribution. In this study, open fields surface dose, dmax and depth dose distribution values were compared with physical wedge filter for 6MV FB and 7MV UFB .The measurement carried out in Siemens - ARTISTE linear accelerator with diode detector along the central axis of the beam at 100 cm source to surface distance using IBA blue water phantom for 6MV FB and 7MV UFB x-ray beams.

Results: The surface dose increased as the field size increased for open and physical wedge fields for 6MV FB and 7MV UFB beams. For open fields, Surface doses relative to the dose at dmax ranged from 0.443 to 0.569 and 0.463 to 0.668 for field sizes of 5 x 5 to 20x20 cm² for the 7MV UFB and 6MV FB beam respectively. The measured surface dose for 150, 300,450 and 600 wedge field values are 0.396 to 0.504, 0.366 to 0.484, 0.342 to 0.464 and 0.347 to 0.47 respectively for 7MV UFB and 0.424 to 0.566, 0.398 to 0.555, 0.3860 to 0.5430 and 0.389 to 0.55 respectively for 6MV FB.

Conclusions: We found that dmax of wedged beams were higher than those open beams for field size up to 10 x 10 cm², Surface doses of wedged beams were lower than those of open beams for 7MV UFB and 6MV FB. Surface dose of the 7MV UFB were lower than the 6MV FB for open and wedged beams.

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