Can The Quality Of A Treatment Plan Predict Complications In Gks For Acoustic Neuroma?

Ian Paddick1, Andras Kemeny2, Neil Kitchen3, Christer Lindquist3, Bodo Lippitz3, Matthias Radatz4

1Medical Physics Ltd 2S Yorks, United Kingdom 3Cromwell Hospital 4 Thornbury Radiosurgery Centre

Keywords: vestibular schwannoma, dose planning, gamma knife, outcome, complications

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     In the treatment of acoustic neuroma with Gamma Knife Surgery (GKS), much attention is placed on scrutinizing the quality of the treatment plan. Whilst refining the treatment plan in terms of conformity and reduction of dose to critical structures should not do any harm, it can often add a great deal of time to the treatment procedure and increase extracranial doses due to increased beam on times.  While the sophistication of treatment delivery has enabled the dramatic increase in conformity of treatments in the last 10 years, complications have not noticeably decreased. This poses the question: Does the quality of the treatment plan really matter?  Several studies have been published exploring the relationship between conformity or gradient on complications. While in studies looking at conformity have lead to contradictory conclusions (Nakamura et al, Korytko et al), the gradient outside an acoustic neuroma treatment plan had a statistically significant effect on resulting complications (Liscak et al).
     A flaw with the conformity or gradient index is that irradiation of different structures is ignored, so irradiation of say, CSF is given the same given the same weight as say, brain stem. Because of this, radiosurgeons consistently point out that a visual inspection of the dose plan is essential for its evaluation.
     Five treatment plans were obtained from patients that had developed complications from GKS for their acoustic neuroma.
     Each treatment plan was then mixed with four randomly selected treatment plans with similar features (tumour volume, shape, surgical history), but whose treatment had not resulted in complications. The five groups of five treatment plans were then shown to four very experienced radiosurgeons, who were asked to select the plan from each group which had resulted in complications. They were shown the isodose plan, conformity indices (Shaw and Paddick), Gradient Index, target volume, prescription dose, isodose and a brief clinical history. In the process, 25 plans were each examined by the four radiosurgeons, resulting in 100 plan inspections.
     Results obtained will be presented.
     This is a retrospective study.
      The simple test results allowed easy statistical testing of the hypothesis that the quality of the treatment plan has a significant impact on the development of complications.
     This test was performed on the entire data, but also on individual radiosurgeons results, as each clinician has different ideas as to what constitutes a safe dose plan.


Project Roles:

I. Paddick (), A. Kemeny (), N. Kitchen (), C. Lindquist (), B. Lippitz (), M. Radatz ()