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SU‐FF‐T‐259: The Impact of Photon Beam Spectra On OneDose MOSFET Dosimeter Response
Author(s) -
Pursley J,
Rand T,
Singerline C,
Ray M
Publication year - 2009
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 - 10.1118/1.3181736
Subject(s) - dosimeter , linear particle accelerator , dosimetry , ionization chamber , imaging phantom , irradiation , photon , physics , beam (structure) , dose profile , optics , nuclear medicine , radiation , materials science , medical physics , ion , nuclear physics , medicine , quantum mechanics , ionization
Purpose: Relate the spectral differences of several dissimilar linear accelerator photon beams to the response of OneDose™ MOSFET dosimeters. Method and Materials: A Virtual Water™ phantom was constructed that mimics recommended usage of the OneDose dosimeter, with simultaneous irradiation of a calibrated ion chamber. The phantom was used for irradiations on Elekta, Siemens and Varian linacs, at photon energies of 4, 6, 10, 15 and 18MV. Field parameters were identical, except that dosimeters and effective point of measurement of the ion chamber were adjusted to d max . Measurements were taken to accurately calculate dose following the TG‐51 protocol. At minimum, 20 dosimeters were irradiated per beam to increase statistical validity of results. Dosimeters were read per manufacturer instructions. Readings were adjusted to 100 cGy dose and normalized to the average of 6MV readings for comparison. Readings from exposure to60 Co were compared to linac results. Response dependence to field size and SSD was also studied at 6MV. Results: Dosimeter responses at like nominal energies are consistent at the 95% confidence level across all linear accelerators in the study. Response decreases linearly by ∼4% from60 Co to 10MV, then becomes nearly independent of energy to 18MV. Response shows no appreciable dependence on SSD from 80–100cm SSD at 6MV, but increases ∼5% with field size from 5cm 2 to 20cm 2 . Conclusion: Similarity of response across different linear accelerators suggests that nominal beam energy is an adequate qualifier for determining OneDose dosimeter energy correction factors. Differences in contamination particles produced in linac head components are not significantly altering response. This conclusion is strengthened by the insensitivity of response to SSD. The increasing response with field size can be attributed to a lower average energy from increased scatter radiation. Conflict of Interest: The authors are employees of Sicel Technologies, Inc.