ZAP-X: A Novel Radiosurgical Device for the Treatment of Trigeminal Neuralgia.

Introduction The treatment of trigeminal neuralgia (TN) is one of the most demanding of all radiosurgery procedures, requiring accurate delivery and sharp dose fall off. ZAP-X®, a new, innovative frameless radiosurgical device, maybe an attractive platform for the treatment of TN and other functional brain disorders. Here, we compared the dosimetry of ZAP-X plans for a single patient to that generated by a well-established dedicated radiosurgery device, the CyberKnife. Methods Radiosurgery plans that delineated the cranial nerve from a single patient's fused computed tomography and magnetic resonance imaging (CT-MR) data set were planned on both the ZAP-X and CyberKnife, with the latter serving as a validated benchmark. The same target and treatment planning constraints were applied. Plans were evaluated by a physician with experience treating TN and a medical physicist. The ZAP-X treatment plan used two isocenters delivered through 4-mm collimators based on a non-isocentric plan that delivered 29,441 MU through 81 beams. The CyberKnife plans used a 5-mm collimator for a non-isocentric plan that delivered 17,880 MU through 88 beams. Results Based on visual inspection, the isodose volumes covered by ZAP-X and CyberKnife were similar at the prescription isodose (70% and 80%, respectively, with a maximum dose (Dmax) of 7500 cGy. The conformality index was better for the CyberKnife as compared to ZAP-X. However, the irradiated volumes were smaller at the 50%, 20%, and 10% isodoses for ZAP-X (0.12 cc, 0.57 cc, and 1.69 for ZAP-X; 0.18 cc, 0.91 cc, and 3.41 cc for CyberKnife). In particular, the 20% and 10% isodose volumes were much smaller for ZAP-X, especially on the axial and sagittal planes. Conclusions ZAP-X treatment planning for TN compares favorably with equivalent planning on CyberKnife. The brain volumes containing the 20% and 10% isodoses are smaller using ZAP-X, thus relatively sparing critical structures close to the target, including the Gasserian ganglion and brainstem. This feature could be of clinical relevance by potentially reducing treatment-related complications.