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SU‐E‐T‐719: Surface Dose Evaluation of the Equivalent Quality Flattening Filter‐Free Photon Beams
Author(s) -
Meshram M,
Pramanik S,
Ranjith C P,
Meshram M
Publication year - 2015
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4925083
Subject(s) - flattening , imaging phantom , beam (structure) , optics , field size , linear particle accelerator , dosimetry , percentage depth dose curve , photon , physics , materials science , nuclear medicine , ionization chamber , medicine , ion , quantum mechanics , ionization , astronomy
Purpose: To provide data on the relative surface dose of photon beams of Versa HD linear accelerator designed to delivered the Flattening Filter Free (FFF) beam having beam quality equivalent to the corresponding Flattened beam.This study involves the comparative evaluation of the entrance dose of FFF and Flattened photon beams in the buildup region. Methods: Surface dose was measured using Markus parallel plate chamber with the thin flat entrance window thickness of 0.025mm of water equivalent material in solid water phantom. Data were collected for square fields of 2×2cm 2 , 3×3cm 2 ,4×4cm 2 ,5×5cm 2 ,7×7cm 2 ,10×10cm 2 and 20×20cm 2 created in Monaco Treatment Planning System.The surface dose was define for this study as the relative dose at depth of 0.5mm with respect to the dose at dmax.The same Markus chamber was used to investigate the dose in the buildup region for all the square fields.The buildup depths for 6MV flattened and FFF beams were 0 to 18mm and for 10MV Flattened and FFF beams were 0 to 24mm. All values were determined in relation to the depth at dose maximum dmax. Results: The relation of surface dose for both Flattened and FFF beams with field sizes were linear. The surface dose for smaller field size upto 10×10cm 2 for both FFF beams were higher than Flattened beams but the variation was marginal. The difference was 0.3 percentage at 6MV and 1.9 percentage at 10MV for a 10×10cm 2 field but for the larger field the relative surface dose was lower for FFF beam with difference of 3.6 percentage at 6MV and 4.3 percentage at 10MV for a 20×20cm 2 field. Conclusion: The equivalent quality FFF Photons produce higher surface dose for smaller field sizes upto 10×10cm 2 but lower surface dose for large field sizes than the conventional flattened beam. The percentage variation was marginal for smaller field sizes and may not be clinically significant.