Room: Exhibit Hall
Purpose: To investigate the timeline and degree of damage created in the mouse brain via irradiation with an X-Rad 320 cabinet irradiator and compare the results to prior work performed with a Gamma Knife.
Methods: PXi Precision X-Rayâ€™s X-Rad 320 unit is used to conduct mice irradiations with a filter having a ~1.0 mm of Cu HVL. Mice are anaesthetized, and critical structures are shielded with 1/4 inches of lead prior to irradiations. Doses from 50 Gy to 100 Gy are delivered to a sub-hemispheric portion of the brain, with the development of necrosis tracked out as long as 26 weeks. Mice are periodically imaged with a 7T Bruker MRI using T2 and post-contrast T1 imaging, and histology is obtained after final imaging is performed.
Results: The irradiation setup reduces the radiation dose to shielded structures by a factor of ~93%. Focal irradiations of 50 Gy failed to produce necrosis in a 26-week span. Doses from 60 to 100 Gy produce necrosis in a timeframe ranging from 16 weeks to 2 weeks. Necrosis imaged with MRI is more T2 sensitive, and histology of mouse brains post-imaging confirms that regions on MRI with abnormal signal correspond to pathology development on histology.
Conclusion: 50 Gy from the X-Rad 320 does not produce radiation injury with the same timeline as 50 Gy planned to the 50% isodose from the Gamma Knife, with the latter producing radiation necrosis starting at 4 weeks. The timeline of necrosis starting and developing in the Gamma Knife model is more similar to a combination of doses between 60 and 100 Gy with the X-Rad 320. This is most likely due to the unique dosimetry of the Gamma Knife radiation planning where the mouse brain receives a dose between 50 and 100 Gy as implied by the 50% isodose.