Room: Exhibit Hall | Forum 3
Purpose: The increasing adoption of small animal image-guided radiotherapy (SA-IGRT) systems has the potential to significantly improve the accuracy and precision of pre-clinical radiotherapy studies. However, SA-IGRT systems are typically housed in radiobiology labs, receiving limited dedicated physics support compared to clinical radiotherapy machines. Here, we develop a set of simple quality assurance (QA) tests using the in-built electronic portal imaging device (EPID) on the small animal radiation research platform (SARRP, XSTRAHL, Inc.), thereby reducing the need for specialized expertise and equipment.
Methods: A year-long characterization of the SARRP EPID was performed to quantify detector warm-up time, stability, short- and long-term reproducibility, gantry angle dependency, output factor, and linearity of response. Subsequently, empirical tests were developed to verify x-ray beam properties â€“ namely, beam energy (kVp), beam quality (HVL - half-value layer), output constancy (dose rate) and profile (flatness/symmetry). In addition, mechanical tests were developed to measure beam targeting accuracy at arbitrary combinations of gantry and couch angles.
Results: EPID response was stable (â‰¤0.3% variation over one fraction), reproducible (â‰¤1.9% variation over one year), uniform and linear with tube current at all energies. Detector response and kVp were closely related, allowing independent verification of kVp stability based solely on the EPID response. HVL values measured with the imager agreed with ion chamber measurements within 7.1%. The beam targeting test showed a beam central axis mean displacement of 0.76 Â± 0.09 mm at gantry 135Â°/couch 0Â° and 0.89 Â± 0.06 mm at gantry 0Â°/couch -135Â°.
Conclusion: We performed the first in-depth characterization of an EPID at kV energies. The EPIDâ€™s stable and reproducible response yielded acceptable results demonstrating its potential use for developing quick and robust QA tests for the SARRP. Beyond the current scope, we expect that this framework may be applied to any SA-IGRT system that incorporates an EPID.