Andrew Gerry (United States of America)
University of Maryland Medical Center Radiation OncologyAuthor Of 1 Presentation
DOSIMETRIC EVALUATION OF A NOVEL COLLIMATOR DESIGN FOR CONCURRENT MURINE HEMITHORAX IRRADIATIONS USING PROTON FLASH-RT
Abstract
Background and Aims
Protons can be delivered at FLASH-RT dose rates, but the Gaussian-shaped scanning spot (σ≈3.74mm) is incapable of sparing other organs in mice irradiations due to the ~20mm size of mice. In this study, we develop and validate a novel collimator for high-throughput hemithoracic irradiations of mice using 250MeV protons delivered at FLASH-RT dose-rates.
Methods
We designed a brass collimator of 7.62cm width (~44cm water-equivalent-thickness) for 250MeV FLASH-RT protons (~38cm range in water). Six 13mm apertures were precision-machined to allow concurrent ipsilateral-lung irradiation of six-mice while sparing contralateral-lung, head-and-neck, and abdominal organs. EBT-XD Gafchromic film was used to measure dose profiles at various depths of solid-water below the apertures to assess radiation penumbra and field size. The RayStation treatment planning system was used to calculate dose volume histograms of the organs.
Results
At 20mm depth, the radiation field showed a sharp profile edge (~0.4mm penumbra) nearly identical to the 320kVp beam historically used to perform hemithorax irradiations. Compared to the standard technique, the collimator allows sparing of the other organs. For 10Gy prescribed dose to the ipsilateral-lung, the collimator lowers the mean dose to the contralateral-lung from 6.3 to 2.7Gy, to the heart from 8.4 to 5.8Gy, to the liver from 8.5 to 6.5Gy, and to the stomach from 3.8 to 1.8Gy.
Conclusions
We designed and constructed a collimator able to perform concurrent hemi-thoracic proton irradiations while sparing other organs. This technique replicates the historical kV x-ray technique and is a vast improvement over using the standard scanning proton beam technique without further collimation.