Proton 3-D-Conformal "Radiosurgery" of Cerebral Arteriovenous Malformations: 3-D Computer Planning, Radiation Methods, the First Results

E.I. Luchin, Yu.G. Budyashov, S.A. Vasilyev, V.N. Gaevsky, I.A. Gulidov, A.V. Iglin, G.V. Mitsyn, A.G. Molokanov, M.A. Tseitlina, E.P. Cherevatenko, S.V. Shidky

United Institute of Nuclear Investigations, Laboratory of Nuclear Problems, Dubna, Russia
Medical Radiologic Research Center, Obninsk, Russia
Sklifosovsky Research Institute of Neurosurgery Department of Emergency Care, Moscow, Russia

 

During the last two-three decades stereotactic radiosurgery, based on use of different apparatus and radiation types (narrow photon beams - a gamma-knife, linear accelerators, proton beams),occupied an important place among methods of treatment of inoperable cerebral arteriovenous malformations (AVM). Proton emission, as compared to photon emission, has some advantages in spatial distribution of a dose.

Modern technology of pre-radiation diagnosis, 3-D computer planning and 3-D realization and verification of a plan of proton irradiation were developed in the United Institute of Nuclear Investigations (UINI) in 200-2001.

Technologic stages of pre-radiation preparation and proton "radiosurgery" were as follows:

The international protocol was used for treatment of patients with AVM, according to which an irradiation target was included into 70-80% of isodose. Applied doses made 25 Gy-equivalents in the isocenter point (1 Gy-equivalent = 1 physical Gy, multiplied by relative biological efficacy of protons, equal to 1.1). A value of doses in the area of target margins was 18-20 Gy-equivalents. There were 2 irradiation sessions, carried out during two consecutive days. There were 2-7 incoming fields, dependent on AVM localization and shape. One irradiation session lasted for an hour.

During the last 3 years proton "radiosurgery" was used in 16 patients with cerebral AVM of different localization. A target volume varied from 1.5 up to 66 cm3. All the patients were considered to be inoperable, i.e. they could not be treated with the help of open or endovascular operations.

It is well-known, that obliteration of AVM vessels in radiosurgical interventions occurs gradually within 6-24 months after treatment. The patients were followed up during more than 24 months (2 cases), 6-12 months (5 cases), up to 6 months (7 cases). Control examinations (MRI and MR-angiography) demonstrated complete obliteration in all 4 patients with the follow-up of more than 24 months. Partial obliteration was watched in 2 out of 5 cases with the follow-up of 6-12 months. The rest patients with shorter catamnesis were not subject to control examination.

A late response to radiation was observed in 1 female in 18 months. It was represented by development of edema in a cerebral hemisphere. Several courses of treatment with dexazon led to edema resolution.

Developed methods of proton "radiosurgery" allow to carry out conformal irradiation of AVM of any size and localization. Complete estimation of efficacy demands further accumulation of data and longer follow-up. It is planned to use a combination of methods (open surgical intervention, endovascular embolization and proton "radiosurgery") for increasing efficacy of AVM treatment.