Constantin Tuleasca1, Ian Paddick2, John W Hopewell3, Bleddyn Jones4, William T Millar5, Hussein Hamdi6, Denis Porcheron7, Marc Levivier8, Jean Régis7. 1. 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. 2. Gamma Knife Centre, National Hospital for Neurology and Neurosurgery, London, United Kingdom. 3. Green Templeton College, University of Oxford, Oxford, United Kingdom. Electronic address: john.hopewell@gtc.ox.ac.uk. 4. Green Templeton College, University of Oxford, Oxford, United Kingdom; Gray Laboratory, CRUK/MRC Oxford Institute for Radiation Oncology, University of Oxford, Oxford, United Kingdom. 5. Beatson Oncology Centre, Gartnavel Hospital, Glasgow, United Kingdom. 6. Functional and Stereotaxic Neurosurgery Service and Gamma Knife Unit, Centre Hospitalier Universitaire "La Timone," Marseille, France; Neurosurgery Department, Tanta University Hospitals, Tanta, Egypt. 7. Functional and Stereotaxic Neurosurgery Service and Gamma Knife Unit, Centre Hospitalier Universitaire "La Timone," Marseille, France. 8. Neurosurgery Service and Gamma Knife Centre, Central University Hospital, Lausanne, Switzerland; Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland.
Abstract
OBJECTIVE: How 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. METHODS: A 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. RESULTS: RE-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. CONCLUSIONS: These 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.
OBJECTIVE: How 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. METHODS: A 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. RESULTS:RE-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. CONCLUSIONS: These 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.
Authors: Lina R Barzaghi; Luigi Albano; Claudia Scudieri; Carmen R Gigliotti; Antonella Del Vecchio; Pietro Mortini Journal: Neurosurg Rev Date: 2021-01-12 Impact factor: 3.042
Authors: Thomas Klinge; Marc Modat; Jamie R McClelland; Alexis Dimitriadis; Ian Paddick; John W Hopewell; Lee Walton; Jeremy Rowe; Neil Kitchen; Sébastien Ourselin Journal: J Radiosurg SBRT Date: 2021