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Poster — Thur Eve — 15: Surface Dosimetric Performance of Superposition‐Convolution Algorithms in Tangential Photon Beams: A Monte Carlo Evaluation
Author(s) -
Chow J,
Jiang R
Publication year - 2010
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 - 10.1118/1.3476120
Subject(s) - imaging phantom , monte carlo method , dosimetry , physics , photon , linear particle accelerator , optics , beam (structure) , superposition principle , convolution (computer science) , isocenter , radiation treatment planning , nuclear medicine , mathematics , radiation therapy , computer science , medicine , statistics , quantum mechanics , machine learning , artificial neural network
Surface dosimetry predicted by the analytical anisotropic algorithm (AAA) and collapsed cone convolution (CCC) algorithm was evaluated using oblique (5° and 45°) tangential photon beams (6 and 15 MV) with different field sizes (4 × 4, 7 × 7 and 10 × 10 cm 2 ), produced by a Varian 21EX linac. Surface dose or phantom skin profiles, at a distance of 2 mm from the solid water phantom lateral surface to mimic skin doses, were calculated by the AAA, CCC and Monte Carlo simulation (EGSnrc‐based code) used as a benchmark for comparison. It was found that doses in the phantom skin profiles were underestimated with small fields for the 6 and 15 MV photon beams, when the gantry angle was set to 5° clockwise. The mean dose differences for the 6 MV (4 × 4 cm 2 ) photon beams were −15.1% (SD = 3.6%) and −3.7% (SD = 1.5%) for the AAA and CCC, while those for the 15 MV (7 × 7 cm 2 ) beams were −12% (SD = 3.5%) and −7.6% (SD = 2%) when compared to Monte Carlo simulations. For larger gantry angle of 45°, the AAA and CCC were found overestimating doses in the phantom skin profiles with different field sizes and beam energies. As surface dose with oblique tangential photon beam is important in radiation treatment sites such as breast, chest wall and sarcoma, the dosimetry data in this study are worthwhile to be considered, when carrying out quality assurance and commissioning for treatment planning systems.