Abstract
Introduction A new formalism has been recently proposed for the dosimetry of small and non-standard fields. In terms of output factor (OF) measurements, a correction factor k(Q(clin),Q(msr)) (f(clin),f(msr)) is introduced, that accounts for differences in the detectors response in a given clinical field, f(clin), with regard to the machine-specific reference field, f(msr). Purpose To derive these correction factors for the 4 mm and 8 mm collimators of Perfexion Leksell gamma knife (LGK) system for the new Razor diode detector providing by IBA for small filed dosimetry. Materials and methods In Perfexion system, f(msr) is defined by the 16 mm collimator. OF measurements were performed for the 4 mm and 8 mm collimators (f(clin)), using the solid water, 16 cm in diameter LGK dosimetry phantom, along with a custom made insert facilitating accurate detector positioning. The k(Q(clin),Q(msr)) (f(clin),f(msr)) factor of the Razor diode detector was determined, by comparing the ratio of detector readings in f(clin) (4 mm and 8 mm collimators) and f(msr) (16 mm collimator) to corresponding MC reference OF data. Results Razor diode was found to slightly overestimate both f(clin) OFs with overestimation being greater for the smaller 4 mm collimator reaching up to 4% and almost negligible ( Conclusion IBA Razor diode can be safely used for OF measurements in gamma knife perfexion system. However, a correction of the order of 4% must be used for accurate determination of the smallest 4 mm collimator.
Published Version
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