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No description available.

The ArcCHECK dosimeter is a novel dosimetry tool that uses a helical array of silicon diode detectors to measure dose in a cylindrical plane. 3DVH is an associated software that can use ArcCHECK diode measurements along with treatment planning system (TPS) data to guide a full 3D dose reconstruction. The ArcCHECK phantom, along with 3DVH software was evaluated as a volumetric modulated arc therapy (VMAT) pretreatment verification tool. The comprehensive evaluation of the ArcCHECK and 3DVH system involved a comparison of measured dose to both ECLIPSE and Monte Carlo calculated dose for open fields and intensity modulated radiation therapy (IMRT) plans. System based confidence limits for gamma-pass rate and dose difference metrics were established through the measurement of prostate and head and neck VMAT plans. Using the system based confidence limits and clinically accepted tolerances, the sensitivity of the ArcCHECK and 3DVH system to VMAT errors was determined. Dose measured by the ArcCHECK and reconstructed in 3DVH agreed very well with dose calculated in ECLIPSE and Monte Carlo for both open fields and IMRT plans. The only results that fell outside of clinically accepted tolerances were a set of head and neck IMRT plans, however it was determined that a major factor in this result was suboptimal modelling of MLC effects in the TPS, in combination with changes in linac performance since commissioning of the TPS model. VMAT measured by the ArcCHECK and 3DVH system were in excellent agreement with ECLIPSE results and system based confidence limits were determined to be tighter than commonly used limits. ArcCHECK and 3DVH were sensitive to clinically relevant VMAT errors and insensitive to errors with little dosimetric impact, although diode measurements alone required tighter tolerances than are typically used. The ArcCHECK phantom and 3DVH software when used together have been shown to provide useful dosimetric information when used for VMAT pretreatment verification. / Graduate / 0756