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Po‐Poster ‐ 12: Evaluation of MOSFETS for Gamma Knife® helmet factor measurements
Author(s) -
Kurjewicz L,
Berndt A
Publication year - 2005
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 - 10.1118/1.2030991
Subject(s) - dosimeter , thermoluminescent dosimeter , dosimetry , calibration , collimator , reproducibility , mosfet , nuclear medicine , materials science , medical physics , physics , optics , medicine , transistor , mathematics , statistics , quantum mechanics , voltage
The Gamma Knife ® is calibrated annually using the 18 mm collimator helmet; the dose rates for the other helmets are determined by measuring the radiation output relative to the 18 mm helmet. These relative measurements yield a helmet factor for each collimator helmet, which is incorporated into the treatment planning software, and is validated during annual quality assurance testing. Traditionally, helmet factors have been measured using 1×1×1 mm 3 thermoluminescent dosimeters (TLDs). Determining helmet factors using this technique is a challenging process since the TLDs are small and fragile, and their preparation, calibration and readout is very time consuming. They also have a large uncertainty of 2 to 5%. The goal of this research is to investigate the use of metal oxide semiconductor field effect transistor dosimeters (MOSFETs) for Gamma Knife® helmet factor measurements. The MOSFET linearity and reproducibility was first characterized using a60 Co teletherapy unit; the linearity and reproducibility were both found to be within 2%. The helmet factors were then measured using TLDs, and again using MOSFETs. The TLD results gave helmet factors within 2.5% of the manufacturer's values; the MOSFETs provided helmet factors within 1.3% of the manufacturer's values, in a fraction of the time it took to generate the TLD results. This investigation confirms that MOSFETs can be used to measure Gamma Knife® helmet factors more quickly and accurately than TLDs.