Optimizing the Small Animal Radiation Research Platform (SARRP) for High-Dose Rate Focal Irradiation Studies

Purpose/Objective(s)The objective of the study is to enable high-dose rate focal irradiation in small animal models through modification of a commercial small animal radiation research platform (SARRP), which is widely used by investigators for preclinical research in radiation oncology. Small animal pre-clinical research is a fundamental part of clinical translation of novel treatment techniques. Currently, the SARRP system only enables dose rate of 3.5 Gy/min at the nominal isocenter. However, preclinical studies to investigate SBRT ablative models, such as those for the lung, liver, and more recently the heart, require much higher dose rates (ideally at least 10-20 Gy/min) and the current SARRP system setup requires long anesthesia time to deliver the required radiation dose to the animals. In addition, emerging applications such as lattice SBRT for larger tumors (which requires the delivery of a large grid of focal irradiation spots in a short time), is currently impossible with the current SARRP system. Here, we present our work to optimize the SARRP system using a modified beam collimation system to allow high-dose rate focal irradiation studies in vivo, while enabling a highly flexible set of collimator sizes and shapes to be used.Materials/MethodsA commercial SARRP system with nominal source-to-axis distance (SAD) of 35 cm was studied in this work. In order to be able to perform experiments at a higher dose rate, a dedicated beam collimation apparatus was designed to provide a short source-to-surface distance (SSD) of 14 cm. Measurements were performed using an ionization chamber and radiochromic film dosimeter to measure the dose rate using the original beam collimation assembly at the isocenter (35 cm SSD), and using our dedicated beam collimation assembly at 14 cm SSD. Measurements were at the surface and at 2 cm depth in phantom with and without the x-ray filter in place.ResultsThe SARRP system with standard collimation assembly provides a dose rate of 3.5 Gy/min at 2 cm depth in phantom at 35 cm SAD. The dose rate measured using our apparatus increased by a factor of 4.9, reaching 17 Gy/min, at 14 cm SSD and 2 cm depth in phantom. Removing the x-ray filter would additionally increase the dose rate by another factor of 6 at the surface and 1.7 at 2 cm depth in phantom.ConclusionThe SARRP system with our modified collimation system would allow in vivo experiments with dose rates of 17-29 Gy/min at 14 cm SSD.