Abstract
The ”Device for Advanced Verification of IMRT Deliveries” — DAVID is a transparent, segmented, multi-wire ionization chamber. It attaches to the accessory holder of the gantry. Each wire is centered to the field defined by a leaf pair. The integrated signal measured in each wire is related to the dose delivered to the patient by the modulated incident beam. Thus, at this time DAVID is the only device able to measure an undisturbed signal, related only to Linac parameters. The software compares the signals measured during the radiotherapy session to a reference acquired during the pre-treatment QA process. DAVID is intended for documenting the radiation delivery constancy of conformal plans, IMRT (Step & Shoot and Sliding window) and RapidArc techniques in real time, during patient treatment. Though not originally intended, DAVID has the potential to perform a number of Linac Physics QA tests. DAVID is a new product in North America. Currently only two are in use, one in New York and the other in Abbotsford, Canada. In order to employ effectively DAVID for routine clinical use, we performed a comprehensive set of measurements. The list includes transmission factors, signal reproducibility with field size and gantry angle, daily setup error of the device, field edge position sensitivity, dose rate signal dependence, EDW constancy, dosimetric leaf gap, picket fence and preliminary work on IMRT verification. All measured data was processed by statistical methods. Our results show that the DAVID system is an effective tool for monitoring IMRT delivery consistency.
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