Abstract
One of the applications of MatriXX (IBA Dosimetry) is experimental verification of dose for IMRT, VMAT, and tomotherapy. For cumulative plan verification, dose is delivered for all the treatment gantry angles to a stationary detector. Experimental calibration of MatriXX detector recommended by the manufacturer involves only AP calibration fields and does not address angular dependency of MatriXX. Angular dependency may introduce dose bias in cumulative plan verification if not corrected. For this reason, we characterized angular dependency of MatriXX and developed a method for its calibration. We found relatively large discrepancies in responses to posterior vs. anterior fields for four MatriXX (Evolution series) detectors (up to 11%), and relatively large variability of responses as a function of gantry angle in the gantry angle ranges of 91°–110° and 269°–260°. With our calibration method, the bias due to angular dependency is effectively removed in experimental verification of IMRT and VMAT plans.PACS number: 87.56Fc
Highlights
MatriXX (IBA Dosimetry, Bartlett, TN) is a 2D detector developed for megavoltage dosimetry.[1,2,3,4] One of its potential applications is experimental verification of patient specific IMRT plans
The user has to experimentally determine kuser factor, which converts the charge collected by the internal electrometer of MatriXX to the dose deposited in the detector plane at a given calibration depth and field size
Asymmetry of the profiles observed for MatriXX with respect to 180° gantry angle may be due to difference of the inherent structure and due to setup, which is more sensitive to misalignment than for A12
Summary
MatriXX (IBA Dosimetry, Bartlett, TN) is a 2D detector developed for megavoltage dosimetry.[1,2,3,4] One of its potential applications is experimental verification of patient specific IMRT (and more recently VMAT) plans. Patient specific dose verification can be carried out with MatriXX either mounted on the rotating gantry or positioned on the treatment couch. In the latter case, cumulative plan dose in a single plane can be measured. Calibration of MatriXX includes correction of gain of individual ionization chambers (kgain factor) and absolute calibration of the detector response (kuser factor). The user has to experimentally determine kuser factor, which converts the charge collected by the internal electrometer of MatriXX to the dose deposited in the detector plane at a given calibration depth and field size (selected by the user). As a result of kuser calibration, the dose measured by MatriXX is absolute
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