Build-up and surface dose measurements on phantoms using micro-MOSFET in 6 and 10 MV x-ray beams and comparisons with Monte Carlo calculations

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

Research output: Contribution to journalArticle

Abstract

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 10 MV 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 0°-80° onto the flat solid water phantom with micro-MOSFET placed at depths of 2 cm, 1 cm, and 2 mm below the surface. Measurements were compared to Monte Carlo calculations under these settings. Finally, measurements were performed with micro-MOSFET embedded in the first 1 mm 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 2 mm thin layer that extends from the surface to a depth of 2 mm. 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 0.87 mm for 6 MV beam and 0.99 mm for 10 MV beam from the flat side, and a WET of 0.72 mm for 6 MV beam and 0.76 mm for 10 MV 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 2 cm, 1 cm, and 2 mm, 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 1.0 mm 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 10 MV beams with an estimated accuracy of ±6%.

Original languageEnglish (US)
Pages (from-to)1266-1273
Number of pages8
JournalMedical Physics
Volume34
Issue number4
DOIs
StatePublished - Jan 1 2007
Externally publishedYes

Keywords

  • Breast cancer radiotherapy
  • Head and neck IMRT
  • Micro-MOSFET
  • Monte Carlo simulation
  • Skin dose
  • Surface dose

ASJC Scopus subject areas

  • Biophysics

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  • Cite this

    Xiang, H. F., Song, J. S., Chin, D. W. H., Cormack, R. A., Tishler, R. B., Makrigiorgos, G. M., Court, L. E., & Chin, L. M. (2007). Build-up and surface dose measurements on phantoms using micro-MOSFET in 6 and 10 MV x-ray beams and comparisons with Monte Carlo calculations. Medical Physics, 34(4), 1266-1273. https://doi.org/10.1118/1.2710951