Enhanced Head Immobilization for Gamma Knife Radiosurgery

Elekta Icon Gamma Knife is a radiotherapy treatment system that delivers very precise doses of radiation to brain tumors, arteriovenous malformations (AVMs), and other neurological conditions. To treat the patient, their head has to remain still and cannot move more than 1.5mm. Currently, high precision is achieved by using a patient-specific thermoplastic immobilization mask on a rigid frame, in conjunction with video tracking of reflective markers placed on the frame and tip of the patient's nose. Head movements that exceed 1.5mm automatically stop delivery so the patient can be repositioned. Experience over the past several years with Gamma Knife at Mary Bird Perkins Cancer Center has shown that the immobilization mask adequately limits side-to-side head motion, but head pronation is not as well controlled. In order to combat this, an add-on brace was created in CAD software and 3D printed using resin. It presses against the upper lip and teeth of the patient to restrict head pronation and thus allow for controlled and uninterrupted treatment. Following the development of the brace, head movement will be tracked with and without the brace, and eventually the performance of the brace will be evaluated during Gamma Knife treatments.