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Calculation of k Q clin , Q msr f clin , f msr for several small detectors and for two linear accelerators using Monte Carlo simulations
Author(s) -
Francescon P.,
Cora S.,
Satariano N.
Publication year - 2011
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 - 10.1118/1.3660770
Subject(s) - monte carlo method , physics , detector , linear particle accelerator , imaging phantom , computational physics , beam (structure) , field (mathematics) , optics , photon , range (aeronautics) , dosimetry , laser beam quality , nuclear medicine , statistics , mathematics , materials science , medicine , pure mathematics , composite material , laser , laser beams
Purpose: The scope of this study was to determine a complete set of correction factors for several detectors in static small photon fields for two linear accelerators (linacs) and for several detectors. Methods: Measurements for Monte Carlo (MC) commissioning were performed for two linacs, Siemens Primus and Elekta Synergy. After having determined the source parameters that best fit the measurements of field specific output factors, profiles, and tissue‐phantom ratio, the generalized version of the classical beam quality correction factor for static small fields,kQ clin , Q msrf clin , f msr, were determined for several types of detectors by using the egs _ chamber Monte Carlo user code which can accurately reproduce the geometry and the material composition of the detector. The influence of many parameters (energy and radial FWHM of the electron beam source, field dimensions, type of accelerator) on the value ofkQ clin , Q msrf clin , f msrwas evaluated. Moreover, a MC analysis of the parameters that influence the change ofkQ clin , Q msrf clin , f msras a function of field dimension was performed. A detailed analysis of uncertainties related to the measurements of the field specific output factor and to the Monte Carlo calculation ofkQ clin , Q msrf clin , f msrwas done. Results: The simulations demonstrated that the correction factorkQ clin , Q msrf clin , f msrcan be considered independent from the quality beam factor Q in the range 0.68 ± 0.01 for all the detectors analyzed. ThekQ clin , Q msrf clin , f msrof PTW 60012 and EDGE diodes can be assumed dependent only on the field size, for fields down to 0.5 × 0.5 cm 2 . The microLion, and the microchambers, instead, must be used with some caution because they exhibit a slight dependence on the radial FWHM of the electron source, and therefore, a correction factor only dependent on field size can be used for fields ≥0.75 × 0.75 and ≥1.0 × 1.0 cm 2 , respectively. The analysis of uncertainties gave an estimate of uncertainty for the 0.5 × 0.5 cm 2 field of about 0.7% (1σ) forkQ clin , Q msrf clin , f msrfactor and of about 1.0% (1σ) for the field output factor,ΩQ clin , Q msrf clin , f msr, of diodes, microchambers, and microLion. Conclusions: Stereotactic diodes with the appropriatekQ clin , Q msrf clin , f msrare recommended for determiningΩQ clin , Q msrf clin , f msrof small photon beams.