A Dosimetric Benchmarking Study Of Gamma Knife Perfexion And Model C For Radiosurgical Treatment Of Mesial Temporal Lobe Epilepsy

Keywords: epilepsy, technique, gamma knife, radiosurgery, dose planning

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     To investigate model-dependent dosimetric differences between the Gamma Knife (GK) 4C and Perfexion models for radiosurgical treatment of mesial temporal lobe epilepsy (MTLE).
     Patients with epilepsy.
     As part of the preliminary tests for a multicenter Phase-III clinical trial of MTLE (ROSE Trial), a treatment plan for a patient with epilepsy was created for the Gamma Knife Perfexion using the GK treatment planning system (LGP version 8.3). The target volume and critical structures were contoured on MR images by the principal investigator (NB) for the trial. The prescription dose was 24 Gy to the 50% isodose line and dose constraints included 10 Gy maximum point dose to the brainstem and 8 Gy maximum point dose to the optical structures. For comparison, a plan was then created for the same imaging studies for the GK 4C using the same contours and dose constraints. Two plugging patterns were used. The delivery time and number of shots for the GK Perfexion and GK 4C plans were compared. In addition, dosimetric parameters such as target coverage and dose to structures at risk were evaluated and compared.
     Both plans satisfied the normal tissue constraints.  The plan for the GK Perfexion required the delivery of 23 shots for a total beam-on time of 223 minutes.  By comparison, the plan for the GK 4C required 37 shots and 469 minutes beam-on time.  The reference dose rate was approximately 2.5 Gy/min for both plans.  In addition, better target coverage was achieved with the Perfexion, as 81% of the target volume received the prescription dose vs. 72% with the 4C plan. However, these are preliminary results from a single planner and other planners may achieve better results. Future plans include additional test cases with multiple planners.
     This is a retrospective study.
     Due to the flexibility and ease of sector blocking, it is possible to achieve a superior and more efficient treatment of MTLE with the Gamma Knife Perfexion.
     Additional study is required to determine optimal planning strategies that will satisfy treatment parameters and improve target coverage while reducing overall treatment times.


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