Evaluation of inverse treatment planning for Gamma Knife radiosurgery using fMRI brain activation maps as organs at risk

Stereotactic radiosurgery (SRS) can be an effective primary or adjuvant treatment option for intracranial tumors. However, it carries risks of various radiation toxicities, including radionecrosis and functional deficits. Current SRS inverse planning algorithms allow efficient inclusion of organs at risk (OARs) in the treatment planning process, which will be spared by setting a maximum radiation dose. In this work we propose using activation maps from functional MRI to map the eloquent regions of the brain and define functional OARs. We evaluate the effects of these functional OARs for Elekta Leksell Gamma Knife SRS inverse treatment planning on open data MRI from 5 subjects. Our results show that fMRI-derived functional OARs can effectively be used to reduce the radiation dose incident on the eloquent brain regions, while maintaining acceptable treatment planning metrics on the tumor targets.