Contribution Of Technological Progress And Influence Of Inter-operator Difference In Gamma Knife Radiosurgery For Arteriovenous Malformation

Tomoyuki Koga1, Masahiro Shin1, Nobuhito Saito1

1Univ. of Tokyo Hospital, Tokyo, Japan

Keywords: gamma knife, vascular malformation, arteriovenous malformation, technique, radiosurgery

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     In microsurgical resection of cerebral arteriovenous malformations (AVM), success of the surgery largely depends on the skill and experience of the operator. 
     On the other hand, in gamma knife surgery (GKS), there has been no study which legitimately evaluate those factors and it is still unknown whether the inter-operator difference influences in the treatment outcome or how much the experience of the operator or the technological progress is reflected on the outcomes.
     Since 1990, we have treated 621 AVM with GKS.
     Until now, each 5 neurosurgeons is in charge of it during a certain period (3 to 6 years) one after another. In our department, the next neurosurgeon in charge received GKS internship from his predecessor for more than 6 months and then became a chief of GKS unit. The applied radiographic images were angiography alone (AG, 1990-1992) at first, then AG+CT (1992-2006), and AG+MRI (2003-) progressively. The dose planning was initially made with KULA, and then the computer software, GammaPlan(1998-). Since 2006, we introduced robotized automatic positioning system on irradiation. The influence of the factors related characteristics of AVM (patient’s age, sex, nidus volume, location, history of hemorrhage, type of venous drainage, maximum diameter) and the applied marginal dose are statistically corrected and the influence of 1) inter-operator difference, 2) the operator’s experience, and 3) the progress of radiographic or radiosurgical technologies was assessed in obliteration rates (OR) and the risk of radiation induced neuropathy (RRIN).
     OR was correlated with neither the operators’ factors nor technological progress. RRIN didn’t change among the operators but decreased in use of CT or MRI at dose planning. Especially in AVM with maximum diameter >3 cm, RRIN decreased in use of Gamma plan (p = 0.0243) and CT or MRI (p = 0.0342). Also, it reduced with the experience of the operator (p = 0.0178).
     This is a retrospective study.
     In OR of AVM after GKS, there was no difference among the operator and depending on the experience.
     The technological progress in dose planning contributed to reducing RRIN associated with GKS, and especially in AVM with larger diameters, this progress and the experience of operator in GKS can contribute to decreasing RRIN. We believe that further technological advancement will improve the outcome of GKS for AVM.


Project Roles:

T. Koga (), M. Shin (), N. Saito ()