OCD
As already mentioned, the radiosurgical concept, as stereotactic neurosurgery in general in the beginning, was developed for functional procedures.
Today, only approximately 2% of the Gamma Knife treatments are for functional disorders. The use of the radiosurgical technique for these indications, with the exception of trigeminal neuralgia, thalamotomy for Parkinson’s disease and soon obsessive-compulsive disorder (OCD), has to be regarded as experimental.
The smallest collimator size, 4 mm, is used when creating small volumes of necrosis in central areas of the brain. A dose of 150-180 Gy prescribed to 100% (=the maximum) will create necrosis in gray and white matter. With this dosimetry, the risk is low of inducing a delayed reaction in the brain tissue adjacent to the target area.
When inducing this small volume of necrosis, the anatomical definition of the target has to be extremely accurate since physiological definition (recording, stimulation) is not available. The lesions produced by radiofrequency electrodes usually cover a larger volume and, consequently, are less specific.
Psychiatric disorders
Bilateral anterior capsulotomy, to block the orbitofrontal-dorsomedial thalamic interconnection with radiofrequency (RF) thermolesioning for severe refractory obsessive-compulsive disorder (OCD), was initiated by Talairach and Leksell in the 1950s and was subsequently used in more than 400 reported cases.
Satisfactory improvement of the patients’ condition on follow-up was found in 50-72% in different series over the years. The same target has also been used in some 50 OCD patients undergoing gammacapsulotomy.
In a prospective study of seven OCD patients, treated in the 1970s with the prototype Gamma Knife, five of the patients had MRI-documented lesions and long-term (>7 years) statistically significant improvement based on elaborate psychiatric ratings by two independent investigators.
In a later study, 5 of 5 OCD but only 2 of 6 non-OCD patients showed statistically significant reduction of the symptoms. In this series, three superimposed isocenters (“shots”) with the 4 mm collimators were used to create a lesion similar in shape and volume to those achieved by RF capsulotomy. The maximum dose was 160 Gy in two patients (one 8 mm collimator shot on each side in one of these patients) and 200 Gy in the other nine.
There was, in these latter cases, a high incidence of reaction (edema) developing in the brain tissue surrounding the target volume. This occurred around 13 of the 18 targets, usually reaching a peak between 6 and 12 months but in two instances as late as 28 months after the treatment. Clinically, this was paralleled by increased incidence of fatigue, apathy, and disinhibition, indicating involvement of the frontal lobes.
The patient treated with 160 Gy and 4 mm collimator lesions had no reaction in the adjacent brain tissue and the clinical result was rated as very favorable.
Anterior capsulotomy and cingulotomy, the preferred psychiatric procedure in the US, are established treatment modalities for some psychiatric disorders, in particular OCD.
As our own recently presented study demonstrates, the results of gammacapsulotomy for OCD are very encouraging with significant improvement in approximately 65% of these very sick, sometimes suicidal, patients.
New England Gamma Knife Center psychosurgery policy:
Experimental, clinical study completed. Expected to soon become established clinical practice. Selected OCD patients are offered bilateral anterior gammacapsulotomy based on the decision of the psychiatric team in this study/protocol.
