Gamma System for Refractory Epilepsy
Between May 1999 and May 2001, 26 patients with refractory epilepsy (RFE) were treated in our center using GKS and 12 of 26 patients had been followed up for at least 6 months. All data of these patients went as follows.
Materials and methods
1. Patient population
Between May 1999 and May 2001, 26 patients with RFE were treated in our center using GKS. The patient population consisted of 15 males and 11 females. The mean age was 26.5 years (range from 8years to 56years). The mean duration of history was 10.6 years (range from 4years to 28years). All patients had undergone systematic antiepilepsy medication for at least 2 years but epilepsy was still intractable.
The possible etiopathogenesises went as follows: encephalitis (2 cases), dystocia anoxemia (5 cases), head trauma (3 cases), and idiopathia (16 cases).
3. Diagnostic tests
All patients underwent many diagnostic tests repeatedly as follows: EEG (electroencephalograph), BEAM (brain electric activity mapping-echoencephalography) MRI, and PET. Both EEG and MEAM showed at least middle abnormality in all patients. Only 7 patients had abnormality on MRI, including temporal atrophy (2 cases), hippocampus atrophy (1 case), hippocampus sclerosis (1 case), focal encephalomalacia (2 cases), and cortex dislocation (1 case). 19 patients had normal images. When patients had fit attack, PET showed there were single or multiple lower blood perfusion focuses, which indicated epileptic lesion. 9 patients had multiple focuses and 17patients had single lesion.
4. Treatment methods
Under local anesthesia, patients were installed the stereotactic head frame. High-resolution 1.5TMRI were obtained. 3 millimeters thick, gadoliniumenhanced axial and coronal MR slices of the brain were obtained with the Spoiled Gradient Recalled Acquisition in Steady State sequence. The imaging data were transferred to the gamma system computer work station via a local net, integrating data of PET including location and size. According to different categories of seizure, targets were classified as follows: 1) simple seizure: location targeted by PET, peripheral dose 10-15Gy; 2) complex major seizure: location targeted by PET plus isolateral amygdala and hippocampus, peripheral dose for amygdala and hippocampus 25-30Gy; 2) general seizure: location targeted by PET plus isolateral amygdala and hippocampus plus anterior 2/3 of callus, peripheral dose 50Gy; 4) absence seizure: location targeted by PET plus anterior 2/3 of callus. Prescription dose was planed on computer and be printed. We used MASEP gamma system (China). All patients were discharged the next day after GKS.
12 patients were followed for at least 6 months. The mean period of follow-up was 13.2 months (range 6-22 months). 11 patients began to have seizure relief 1 month later after GKS and have medication decrease and have medication decrease 6 months later after GKS. 4 patients had seizure free (33.3%). 2 patients had seizure decrease >50% (16.7%). One patient had no seizure relief at all (8.3%). Excellent rate, total efficacy, and poor efficacy were 75.0%, 91.7%, and 8.3%, respectively. All patients in this study had no complications and were still survival.
Epilepsy is a medical refractory dilemma in the world, however in recent ten years; surgery has refreshed the treatment for it. The concept of GKS for refractory epilepsy was inspired from the treatment of AVM using gamma system1.3. With the advances in the orientation of epilepsy lesions, especially in incorporation of PET, the efficacy of GK for epilepsy has been greatly increased. So integrating the type of seizure, the precise orientation of epilepsy lesions is the pivot of GSK. Comparing the results between our study and Zhen Ligao et al4 , we thought that difference (efficacy rate in our study and Zhen抯 was 91.7% and 86.5%, respectively) was mainly involved with all targets located incorporation of PET. Then we will focus on two important topic of GK for epilepsy as follows:
1. The orientation of target for epilepsy in GKS
1.1 Location targeted by PET is viable for simple partial seizure (PET and MRI locations are concordant) and seizure induced by brain encephalomalacia alone.
1.2 Locations targeted by PET plus isolateral amygdala and hippocampus: viable for complex temporal seizure.
1.3 Locations targeted by PET plus isolateral amygdala and hippocampus plus anterior 2/3 of callus: viable for complex major seizure
1.4 Location targeted by PET plus anterior 2/3 of callus: viable for absence temporal major seizure
2. Irradiation dose
2.1 Location targeted by PET: lesion targeted by PET usually is normal on MRI image. In our study, only 7 patients showed epileptic lesion on MRI. It is generally accepted that an epileptically abnormal neuron is more susceptible to irradiation than normal one, so only if gamma system delivers a lower dose of energy to an epileptic neuron, its abnormal activity will be suppressed so as to control abnormal over excess discharge in lesions and of course seizure stops. At present, 10-15Gy peripheral dose is accepted. It depends on lesion volume. 13-15GY peripheral dose4 is for lesion diameter<2cm while 10-12Gy peripheral dose is for lesion diameter>2cm.
2.2 Amygdala and hippocampus: in order to destroy them, irradiation dose is large and peripheral dose is 25-30GY7.
2.3 Anterior 2/3 of callus: in order to interdict unilateral epilepsy discharge to other side., anterior 2/4 of callus is excised, which is supported by conventional surgery in early time. However, now we can us GK to get the same effectiveness as conventional surgery. Detail methods are as follows: we use 4 mm collimator, 50% isodose line encompasses the anterior 2/4 of callus, peripheral dose is 50Gy, and central dose is 100Gy4.5.
In conclusion, gamma system is a noninvasive, safe, and effective method to manage refractory epilepsy. In clinic, target for gamma system surgery should be based on the type of seizure integrating many diagnostic tests including PET, EEG, and MRI etc, of which PET is the most important. Combination of multiple targets treatment modality is very important to increase the efficacy. The short-term outcome of gamma system for epilepsy is pleasing; however, its long-term efficacy deserves further demonstration and observation.
1. Steriner L,Lindquist C.Adler J,et al.clinical outcome of rodiosurgery for cerebra1 AVM.J Neurosurg,1992;77:5
2. Rossi GF,Scerrati M,Roselli R.EPileptogeniccerbral low-grade tumors: Effect of interstital atereotactic irridation on seizures.Appl neurophsiol,1985;16:130
3. Inoue HK.ohye C,Ta kahashi A,et al.Gamma knife surgery for lesional epilepsy.The Proceeding of 8th International meeting of the leksell Gamma Knife Society. Marseille,France,1993,141
4. Zhen Ligao, Xu, Desheng, Zhang Zhiyuan, et al. Gamma knife surgical therapy for refractory, j. stereotactic and functional neurosurgery, 1999 :1(2):23
5. Zhen Ligao, Chenpeng, Yang Naiming et al. gamma knife for refractory (affiliated 2 case reports), j. stereotactic and functional neurosurgery, 1995;8(3):29
6. Barcia-salorio JL,Vanc1o cha,V,Cerda M,et a1.Response of perimental epileptic focus to focalionizing radiation. Appl neurophysiol, 1987;50:360
7. Regis J Reragut J C,Rey M,et al.First selective amygda1ohippocampal radiosurgery for攎esial Tamporal Lobe Epilepsy/. Stereo Funct neurosurg, 1995:64(suppl):197