• Constantin Tuleasca, Ian Paddick, John W Hopewell, Bleddyn Jones, William T Millar, Hussein Hamdi, Denis Porcheron, Marc Levivier, and Jean Régis.
• Neurosurgery Service and Gamma Knife Centre, Central University Hospital, Lausanne, Switzerland; Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland; Signal Processing Laboratory, Swiss Federal Institute of Technology, Lausanne, Switzerland; Faculté de Médecine, Sorbonne Université, Paris, France; Assistance Publique- Hôpitaux de Paris, Hôpitaux Universitaires Paris Sud, Centre Hospitalier Universitaire de Bicêtre, Paris, France.
• World Neurosurg. 2020 Feb 1; 134: e204-e213.

ObjectiveHow variations of treatment time affect the safety and efficacy of Gamma Knife (GK) radiosurgery is a matter of considerable debate. With the relative simplicity of treatment planning for trigeminal neuralgia (TN), this question has been addressed in a group of these patients. Using the concept of the biologically effective dose (BED), the effect of the two key variables, dose and treatment time, were considered.MethodsA retrospective analysis was performed of 408 TN cases treated from 1997 to 2010. Treatment involved the use of a single 4 mm isocenter. If conditions allowed, the isocenter was placed at a median distance of 7.5 mm from the emergence of the trigeminal nerve from the brain stem. The effects were assessed in terms of the incidence of the complication, hypoesthesia, and in terms of efficacy using the incidence of pain free after 30 days and 1 and 2 years. These responses were evaluated with respect to both the physical dose and the BED, the latter using a bi-exponential repair model.ResultsRE-evaluation showed that the prescription doses, at the 100% isodose, varied from 75 to 97.9 Gy, delivered in 25-135 minutes. The relationship between the physical dose and the incidence of hypoesthesia was not significant; the overall incidence was ∼20%. However, a clear relationship was found between the BED and the incidence of hypoesthesia, with the incidence increasing from <5% after a BED of ∼1800 Gy2.47 to 42% after ∼2600 Gy2.47. Efficacy, in terms of freedom from pain, was ∼90%, irrespective of the BED (1550-2600 Gy2.47) at 1 and 2 years. The data suggested that "pain free" status developed more slowly at lower BED values.ConclusionsThese results strongly suggest that safety and efficacy might be better achieved by prescribing a specific BED instead of a physical dose. A dose and time to BED conversion table has been prepared to enable iso-BED prescriptions. This finding could dramatically change dose-planning strategies in the future. However, this concept requires validation for other indications for which more complex dose planning is required.Copyright © 2019 Elsevier Inc. All rights reserved.

15 keywords...

hide…