Assessment of an image-guided neurosurgery system using a head phantom.

OBJECTIVE: To acknowledge the challenges and limitations of image-guided neurosurgery systems, we compared the application accuracy of two different image registration methods for one commercial system. (VectorVision, BrainLab, Germany). METHODS: We used an anthropomorphic head phantom for radiosurgery and a custom built add-on to simulate surgical targets inside the brain during an image-guided neurosurgery. We used two image registration methods, fiducial registration using attachable surface markers for computed tomography (CT) and surface registration using infrared laser face scanning. After simulation, we calculated the three-dimensional (3D) distance between the predicted position of a target, and its actual position using a registered pointer and an infrared camera. Deviations were measured for both superficial fiducial markers and internal surgical targets by five different users. RESULTS: Deviations from the location of fiducial markers after each registration method were 2.15 ± 0.93 mm after CT surface marker registration and 1.25 ± 0.64 mm after infrared face scanner registration. The mean target registration errors were 2.95 ± 1.4 mm using fiducial registration and 2.90 ± 1.3 mm using surface registration. The largest deviations (6.2 mm) were found for the targets in the skull base and posterior cranial fossa. Fiducial deviations and target registration errors were statistically uncorrelated. The total application accuracy was 4.87 ± 0.97 mm after CT surface marker registration and 4.14 ± 0.64 mm after infrared face scanner registration. CONCLUSIONS: Despite others have reported differences, we did not find significant variations between both registration methods for the target registration error, although application accuracy was slightly better after surface face registration. Superficial registration errors, but not the target registration error, can be routinely evaluated in the operating room. Since both errors were uncorrelated, surgeons may neglect the achievable accuracy of the procedure. The described method is recommended to assess application accuracy in the operating room.

Stereotactic radiosurgery for pediatric patients with intracranial arteriovenous malformations: variables that may affect obliteration time and probability.

INTRODUCTION: It is debatable whether pediatric patients diagnosed with arteriovenous malformations (AVMs) should be treated as adults. Several indexes to classify AVMs have been proposed in the literature, and most try to predict the outcome for each specific treatment. The indexes differ in the variables considered, but they are all based in adult populations. In this study, we analyzed the variables that influence the obliteration time and probability of occurrence in a Mexican pediatric population diagnosed with an AVM and treated with stereotactic radiosurgery (SRS). METHODS: We analyzed 45 pediatric patients (<18 years) with a minimum follow-up of 10 months and a maximum of 112 months. We used logistic regression analysis and Kaplan-Meier curves to evaluate the influence of age, AVM volume, prescribed dose, minimum dose, maximum dose, time of follow-up, sex, previous hemorrhage, venous drainage, treatment technique, previous treatment and location. We also evaluated the predictive power of the following indexes: Spetzler-Martin, RBAS, or K index dose deviation. RESULTS: We found that the radiation technique used may influence the obliteration occurrence (p=0.057). The data suggests that circular arcs are a more efficient treatment technique than dynamic arcs. However, no relationship of dose or volume with treatment technique could be found. Obliteration was also dependent on follow-up time and after three years of follow-up, the obliteration probability decreases (p=0.024). According to Kaplan-Meier analysis, the nidus obliteration time was related with the location according to the Spetzler-Martin index. If the nidus was located in a non-eloquent region, there was a tendency of a shorter obliteration time (p=0.071). CONCLUSION: None of the previously proposed indexes for adults predict obliteration in this pediatric population. Treatment technique, eloquence and follow up time were the only variables that showed influence in obliteration. Since the highest probability of obliteration occurs during the first three years, if the nidus has not been obliterated after this time then another treatment option could be considered.