Room: Exhibit Hall | Forum 4
Purpose: It has been shown in animal experiments that ultra-high dose rate radiotherapy (FLASH) can spare normal tissue while still providing tumor control. Currently, there is no end-to-end solution for creating and validating proton FLASH treatment plans. This study demonstrates the ability to generate treatment plans and perform dosimetry for FLASH animal irradiations using a clinical ProBeamâ„¢ system.
Methods: FLASH deliverable treatment plans were generated using both Eclipseâ„¢ and a custom Python script. All plans were generated at a single energy with the goal of creating a uniform field in the plateau region of the proton Bragg peak. Measurements were performed at 244 and 250 MeV using a custom, non-clinical machine configuration in service mode. Next, both a PTW 8 cm diameter transmission ion chamber and a Faraday cup were irradiated with a single spot at different beam currents, and the correlation between the measurements was analyzed. In order to establish the absolute dose per field, the large ion chamber was cross-calibrated with a PTW Advanced Markus Chamber at conventional dose rates. Finally, the relationship between dose rate and maximum field size was explored.
Results: The PTW large ion chamber was found to agree well with the Faraday cup with an RÂ² value > .99 up to 360 nA of nozzle current. The maximum field size that could be delivered at an average rate of 100 Gy/s in the plateau region was 27x25 mm.
Conclusion: We have demonstrated a method for planning and validating FLASH treatments for animal irradiations. This approach can be used for future experiments to further explore the benefits of FLASH.
Funding Support, Disclosures, and Conflict of Interest: Many of the authors are employees of Varian Medical Systems.