Design of an Anthropomorphic Intensity Modulated Radiation Therapy Quality Assurance Phantom

The dynamic nature of IMRT delivery poses unique problems relating to the accurate and reproducible quality assurance of dose delivery. The usefulness of point detectors is limited to static fields and regions within low dose-gradients for treatment verification. However, dose distributions generated in intensity modulated radiation therapy (IMRT) often have complex shapes with high dose gradient regions surrounding critical patient structures. Currently, there is no standardized tool for evaluating IMRT treatment delivery. As part of its commitment to the Advanced Technology Consortium, the Radiation Physics Center (RPC) is developing an anthropomorphic quality assurance phantom for the purpose of reviewing IMRT treatment modalities at institutions participating in future NCI cooperative clinical trials. The phantom will verify the ability of institutions to meet the criteria for field localization and three-dimensional dose delivery for IMRT treatments. Specifically, the design of the phantom will allow the measurement of target dose homogeneity to within 5%, field localization for high dose-gradient regions to within 2mm, and absolute dose to isocenter to within 5%. In this poster we present the development of a quality assurance tool for use in the verification of IMRT delivery modalities used in dose-escalated conformal therapy of the prostate. These treatment modalities include the MIMiC arc delivery system, dynamic MLC, and compensators.