Brain Low-risk Aneurysm Stereotactic Radiosurgical Trial

"All treatments will be performed using the Gamma Knife Perfexion or Icon system (Elekta). The following treatment parameters will be used:~* The head will be immobilized using a stereotactic Leksell Model G frame, installed using local protocols~* Targeting will be performed by using a stereotactic CTA. No MRI will be performed.~* Only one aneurysm will be treated per patient~* The aneurysm, including its neck, will be contoured and targeted using a combination of 4mm isocenters as deemed appropriate by the treating team~* A prescription dose of 25 Gy at the margin of the target will be used~* The maximal dose on optic pathways will be kept below 10 Gy~* The brainstem 12-Gy volume will be kept below 1cc"