Use Of Tomotherapy For Stereotactic Irradiation Of Brain Lesions: Comparison With The Leksell Gamma Knife

Keywords: gamma knife, physics, tomotherapy, dose delivery, radiosurgery

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     The Leksell Gamma Knife is considered the reference technique in brain radiosurgery.
     We investigated the feasibility of using a Tomotherapy device for the treatment of small brain lesions with a radiosurgical approach.
       12 patients were studied.
     We first evaluated the « theoretical » possibilities of Tomotherapy by re-planning 12 patients treated with the Gamma Knife. The quality indices (coverage, conformity, homogeneity and dose gradient) were then compared and discussed. The second part of the study consisted of measurements with Gafchromic EBT films to assess the ability of the device to deliver the planned dose for very small targets. In the last part we discussed the important aspect of positioning by reviewing several studies assessing the spatial accuracy of both Gamma Knife and Tomotherapy.
     The main restricting aspect is the dose gradient that is much sharper in Gamma Knife treatments; if one desires to treat a brain lesion with hypofractionated tomotherapy, it has to be taken care of the low-dose spillage to the normal tissue. However the conformity of the prescription isodose and the sparing of the organs-at-risk could be kept at a level equivalent to that of Gamma Knife. The dosimetric measurements showed a good correlation for both the dose profile comparison and the gamma distributions (with threshold 1 %/1 mm), suggesting that the system is not limited by the size of the target. Finally, the results on the positioning in Tomotherapy suggest that despite the additional sources of errors, a high accuracy can be achieved through the MVCT-based corrections, allowing to reach submillimetric accuracy.
     This is a retrospective study.
     Although it remains to evaluate the clinical benefit of such a method, radiosurgical tomotherapy seems technically feasible.
     Radiosurgical tomotherapy allows for time saving and multi-purpose use of the device. However Tomotherapy could not produce dose gradients as high as the ones obtained with the Gamma Knife.


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