Design of an anthropomorphic intensity modulated radiation therapy quality assurance phantom

The Radiation Physics Center (RPC), as part of its commitment to the Advanced Technology Consortium, is developing an anthropomorphic quality assurance phantom for the purpose of reviewing IMRT treatment modalities at institutions participating in NCI cooperative clinical trials. This study investigates the use of an inhomogeneous anthropomorphic phantom for dose verification of IMRT delivery modalities (compensators, dynamic MLC and serial tomotherapy) used in conformal therapy of the prostate. Because the phantom must be mailable, if is lightweight and water-fillable. It is heterogeneous with two interchangeable inserts. The first insert, used to acquire CT data, contains an imageable target and imageable critical structures with densities similar to human tissue densities. This insert provides realistic geometries for dose constraints used in treatment planning. The second insert, used to acquire dosimetry data, contains precisely placed TLD and radiochromic film. This insert will measure target dose homogeneity to within 5% of the treatment plan calculated doses. It will measure field localization for high gradient regions to within 2 mm of the treatment plan. The phantom will be tested for reproducibility and for ease of use at remote locations. Treatments will be planned on the phantom CT data set. Treatment plans for different IMRT treatment techniques will be comparable in both clinical requirements and dose constraints. With a focus on "common" clinical errors, tests will be devised to investigate the capability of this QA system to identify the magnitudes and origins of certain dose and field localization errors.