TU‐C‐BRD‐04: Development and Application of a Pre‐Clinical Stereotactic Irradiator

With the advent of advanced image‐guidance technologies, stereotactic body radiation therapy (SBRT), the application of an ablative dose of radiation given in one or few fractions and delivered with high accuracy, has emerged as a promising modality in the treatment of cancer. Despite this success, there is remains room in optimizing delivery and understanding response. In this regard, pre‐clinical studies can be very beneficial in systematically evaluating response and predicting and validating clinical protocols. We describe the development and application of a small animal irradiator, which provides high accuracy in target localization and radiation delivery in a manner that mimics clinical SBRT delivery. The essential characteristics of the irradiator include: a high dose rate (⩾ 10 Gy/min), allowing high dose delivery in a clinically‐relevant time frame; precise target localization (⩽ 1 mm) to optimize irradiation to a tumor with respect to normal tissue sparing; and small radiation fields (1 to 10 mm) needed to implement the technology in small animals. The irradiator is based on a commercial X‐ray device (XRAD 320, Precision X‐ray, Inc.). The system can be operated at low energies (20–30 kVp) for high contrast imaging (essential for precise localization), and at high energies (⩾ 250 kVp) for therapeutic delivery. Radiation beam parameters, including energy specification (characterized by the half‐value layer — HVL), depth dose characteristics, and off‐axis profiles, have been determined through direct measurement. We describe the application of the device in a number of subcutaneous tumor, orthotopic tumor, and normal tissue models developed at our institution. Finally, the development of a next‐generation irradiator is also discussed.