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Build‐up and surface dose measurements on phantoms using micro‐MOSFET in 6 and x‐ray beams and comparisons with Monte Carlo calculations

2007; Wiley; Volume: 34; Issue: 4 Linguagem: Inglês

10.1118/1.2710951

2473-4209

Hong Xiang, Jun S. Song, A. Taracchini, Robert A. Cormack, Roy B. Tishler, G. Mike Makrigiorgos, Laurence E. Court, Lee M. Chin,

Radiation Therapy and Dosimetry

This work is intended to investigate the application and accuracy of micro‐MOSFET for superficial dose measurement under clinically used MV x‐ray beams. Dose response of micro‐MOSFET in the build‐up region and on surface under MV x‐ray beams were measured and compared to Monte Carlo calculations. First, percentage‐depth‐doses were measured with micro‐MOSFET under 6 and beams of normal incidence onto a flat solid water phantom. Micro‐MOSFET data were compared with the measurements from a parallel plate ionization chamber and Monte Carlo dose calculation in the build‐up region. Then, percentage‐depth‐doses were measured for oblique beams at onto the flat solid water phantom with micro‐MOSFET placed at depths of , , and below the surface. Measurements were compared to Monte Carlo calculations under these settings. Finally, measurements were performed with micro‐MOSFET embedded in the first layer of bolus placed on a flat phantom and a curved phantom of semi‐cylindrical shape. Results were compared to superficial dose calculated from Monte Carlo for a thin layer that extends from the surface to a depth of . Results were (1) Comparison of measurements with MC calculation in the build‐up region showed that micro‐MOSFET has a water‐equivalence thickness (WET) of for beam and for beam from the flat side, and a WET of for beam and for beam from the epoxy side. (2) For normal beam incidences, percentage depth dose agree within 3%–5% among micro‐MOSFET measurements, parallel‐plate ionization chamber measurements, and MC calculations. (3) For oblique incidence on the flat phantom with micro‐MOSFET placed at depths of , , and , measurements were consistent with MC calculations within a typical uncertainty of 3%–5%. (4) For oblique incidence on the flat phantom and a curved‐surface phantom, measurements with micro‐MOSFET placed at agrees with the MC calculation within 6%, including uncertainties of micro‐MOSFET measurements of 2%–3% (1 standard deviation), MOSFET angular dependence of 3.0%–3.5%, and 1%–2% systematical error due to phantom setup geometry asymmetry. Micro‐MOSFET can be used for skin dose measurements in 6 and beams with an estimated accuracy of .