Vim Targeting In Gamma Knife Radiosurgery For Intractable Tremor: Influence Of The Shot Topology On Efficacy And Safety

Kyo Jung Lee1, Adyl Melhaoui2, Tatiana Witjas3, Michael C. Park2, Jean Regis4

1Asan Medical Center 2 Department of Stereotactic and Functional Neurosurgery 3Department of Neurology, Movement Disorders, Timone University Hospital, Marseille, France 4

Keywords: tremor, thalamotomy, gamma knife, outcome, dose planning

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     Although DBS remains the gold standard in surgical treatment for movement disorders, the Vim GKR is becoming an attractive method for tremor with predominant upper limb involvement. 
     This study evaluated the relationship between targeting method and patient outcome.
     Between April 2004 and October 2009, 35consecutive cases (26 males, 9 females, mean age 71) of intractable tremor were treated in Timone University Hospital. Patients underwent imaging, including CISS MR ventriculography for targeting and recently DTI for capsula interna sparing. 
     Vim was targeted (single 4-mm isocenter, maximum dose of 130Gy) using Guiot method and adjusted using DTI to calculate the final dosimetry. For improved safety, the shot was frequently shielded and adjusted anteriorly, superiorly and mesially. Follow up included serial MRIs and clinical evaluations (Whiget tremor scale, functional scale) at 3, 6 months, 1 and 2 years.
     Among 35 patients, 24 had essential tremor (1 post DBS) and 11 had Parkinsonian tremors left target in 27 cases (77%), right in 8 cases (23%). Follow-up was greater than 6 months for 21 patients (range 6-36). Outcome was excellent (>75% improvement) in 12 patients (57.1%), good (50-75% improvement) in 6 (28.6%), and failed (less than 50% improvement) in 3 (14.3%), thus 85.7% (18/21) of patients showed improvement. Follow-up MRI showed T2-hyperintense signal changes and mild gadolinium enhancement at 3 months and variable marked residual cavity after 1 year. One patient developed transient hemiparesis, who showed extensive hyperintense signal changes on the follow-up MRI. Analysis of the targeting coordinates revealed that the failed cases were trending more anterior and superior to the Guiot target.
     This is a retrospective study.
     Target location within the Guiot Vim area was a good predictor of positive clinical outcome in Vim GKR. 
     The failure may be due to the tendency to adjust the target anteriorly and superiorly to avoid the capsula interna, which was later minimized using DTI. Risk of failure or toxicity may also depend on the pathophysiology of the tremor and/or genetic individual factors. Vim GKR could be an efficient and safe procedure for intractable tremor of predominant unilateral tremor patients.


Project Roles:

K. Lee (), A. Melhaoui (), T. Witjas (), M. Park (), J. Regis ()