Functional Gamma Knife Radiosurgery
Movement disorders
Parkinson's disease (PD) has been treated with ventrolateral thalamotomy at some Gamma Knife sites. The results were relatively promising with freedom from tremor reported by Young in three out of four patients followed for at least 6 months. Improvement was reported as early as 24 hours after the treatment.
Some attempts to use closed radiosurgical lesioning to duplicate the excellent results obtained by Laitinen and co-workers following open pallidotomies were less successful and were abandoned. The potential necessity of using physiological as well as anatomical targeting in thalamotomy for tremor is an ongoing controversy.
New England Gamma Knife Center movement disorder policy:
Experimental. There is a protocol for pallidotomy in PD patients. Four patients have been treated. There are currently no plans to enter further patients into this study. Thalamotomy for PD might be considered if for some reason an open stereotactic procedure (lesioning or deep brain stimulation) is not possible.
Pain
The Gamma Knife technique was used early for thalamotomies and hypophysectomies to control pain. These procedures were almost exclusively used for patients with intractable pain related to malignant disease.
Following a latency period of from hours (hypophysectomies) to several weeks, they were frequently effective in reducing the pain. As for the corresponding open procedures, there is a higher risk of recurrence of the pain with these very central targets, which usually make them less suitable for patients with chronic pain not induced by cancer.
Nevertheless, in a study by Young, 17 patients of 27 (63%) with chronic pain, followed at least 6 months after medial Gamma Knife thalamotomy, had experienced good or excellent pain relief. Bilateral cingulotomy might be considered in selected cases of intractable pain with inadequate response to thalamotomy.
New England Gamma Knife Center pain policy:
Experimental. Increasing clinical evidence from several GK centers indicate that thalamotomies and cingulotomies may vindicate a role in the clinical armamentarium when other treatment options for severe chronic pain have been unsuccessful.
Trigeminal neuralgia
As mentioned, radiosurgery was used early for trigeminal neuralgia (tic douloureux). Leksell and Håkanson used two different targets, the root just before entering Meckel’s cave and the gasserian ganglion.
These structures were not easily defined before the advent of MRI. The localization was either based on bony landmarks (the root) or cisternography (the ganglion). In this latter group, 59% (13/22) of the patients were pain free six months after the treatment but only 4 (18%) after 30 months.
Today, the trigeminal root immediately before entering the pons is the preferred target. In a multi-center study, as reported by Kondziolka, 50 patients were treated with a single 4 mm collimator shot. Maximum doses varying between 60 and 90 Gy were delivered.
Following a dose of at least 70 Gy, there was complete pain relief in 53% and at least 50% improvement in another 40% of the patients seven months after the treatment.
At 18 months, the corresponding figures were 48% and 29%, respectively. Three patients (6%) developed increased facial numbness and tingling after radiosurgery, which resolved completely in one and improved in another.
The treatment of trigeminal neuralgia with Gamma Knife radiosurgery is no longer experimental. This technique has a place in the routine armamentarium, which also includes radiofrequency and glycerol rhizotomy, and microvascular decompression, if carbamazepine (Tegretol®) medication has failed.
New England Gamma Knife Center trigeminal neuralgia policy:
Established clinical practice. Can be offered to any trigeminal neuralgia patient where medication has failed. Certain insurance companies require trial with medication and one invasive procedure before covering for Gamma Knife treatment.
