ZAP-X: A Novel Radiosurgical Device forthe Treatment of Trigeminal Neuralgia

Neurosurgery, Cyberknife Center, Centro Diagnostico Italiano, Milano, ITA 2. Department ofRadiation Oncology – Radiation Physics, Stanford University School of Medicine, Palo Alto, USA 3.Department of Neurosurgery, Stanford University School of Medicine, Palo Alto, USA 4. Engineering, ZapSurgical Systems, San Carlos, USA 5. Radiation Oncology, Stanford University Medical Center, Stanford,USA 6. Department of Neurosurgery, Stanford University School of Medicine, Stanford, USA

Introduction

The treatment of trigeminal neuralgia (TN) is one of the most demanding of allradiosurgery 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 TNand other functional brain disorders. Here, we compared the dosimetry of ZAP-X plans for asingle patient to that generated by a well-established dedicated radiosurgery device, theCyberKnife.

Methods

Radiosurgery plans that delineated the cranial nerve from a single patient’s fused computedtomography 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 andtreatment planning constraints were applied. Plans were evaluated by a physician withexperience treating TN and a medical physicist. The ZAP-X treatment plan used two isocentersdelivered through 4-mm collimators based on a non-isocentric plan that delivered 29,441 MUthrough 81 beams. The CyberKnife plans used a 5-mm collimator for a non-isocentric plan thatdelivered 17,880 MU through 88 beams.

Results

Based on visual inspection, the isodose volumes covered by ZAP-X and CyberKnife were similarat the prescription isodose (70% and 80%, respectively, with a maximum dose (Dmax) of 7500cGy. The conformality index was better for the CyberKnife as compared to ZAP-X. However, theirradiated 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, thusrelatively sparing critical structures close to the target, including the Gasserian ganglion andbrainstem. This feature could be of clinical relevance by potentially reducing treatment-relatedcomplications.