When Does Brain Motion Interfere with the Accuracy of Stereotactic Radiosurgery? Investigation of Brain Motion in the Presence of Stereotactic Frame.

Dee H. Wu¹, Jesse Hatfield¹, Jignesh Modi¹, Genu Mathew¹

The aim of stereotactic radiosurgery is to provide accurate placement of radiation localized to targeted diseased tissues while minimizing placement of large doses of radiation into sensitive normal tissues (such as motor strip, brain stem, internal capsule, optic nerve, and other major nerve bundles). It is well known that the brain moves during the cardiac cycle in which the action of pulsatile blood flow produces brain expansion and contraction. Such movement provides a potential conflict with the objective of providing millimeter to submillimeter localization accuracy of radiation treatment. This has led to recommendations for the use of electronic gating of radiosurgery placement. While brain motion was extensively studied in the early 1990s(1, 2), and has been a source of debate for more recent studies for the degree of head fixation required for patients for presurgical planning with fMRI (3). Such brain motion has been cited to be on the order of 0.5 mm for controlled studies over a short period of time (minutes), to 1-3 millimeters over the course of an fMRI experiment when standard to minimal head fixation is used (4). None of these studies were performed with such stringent fixation as that provided during radiotherapy. The frames such that include head fixation with the insertion of metal pins attached to the patient skull with metallic frames.