Abstracts

RATIONALE: Stereotactic radiosurgery (SRS) is used for the treatment of cryptogenic mesial temporal lobe epilepsy (MTLE) as an alternative to conventional anterior temporal lobectomy (cATL). Nonetheless, optimal dose and volume irradiated remain undetermined. We hypothesized that (1) optimal radiation dosing of SRS for MTLE may be less than current reports; (2) magnetic resonance spectroscopy (MRS) may demonstrate changes associated with seizure remission; and (3) MTLE treated with low dose SRS would have better neuropsychological (NP) outcomes compared to cATL. The objective of the participant is to assess low dose SRS for treatment of MTLE.
METHODS: Inclusion criteria: (1) VideoEEG: unilateral MTLE ictal onset; (2) Neuroimaging: ipsilateral (IL) asymmetry of hippocampal volumes with reduced MRS NAA/Cr+Cho ratio; (3) NP testing: no disconcordant findings; and (4) WADA: adequate isolated contralateral hemispheric memory. Both patients received 15 Gy at the 70% isodose level via a 6 mV LINAC SRS device. The volumes irradiated corresponded to the area proposed for cATL for each patient (11 cc and 7.5 cc for Patient 1 and 2, respectively).
POPULATION: Two patients demonstrated left MTL seizure foci on videoEEG with concordant ipsilateral hippocampal atrophy, decreased NAA/Cr+Cho ratios, and NP profiles. Patient 1 and Patient 2 are 25 and 13 months post-SRS, respectively. OUTCOME: Prior to SRS, Patient 1 had complex partial seizures 2-4 times per week and one secondary generalized seizure per month and Patient 2 had monthly seizure clusters of up to 8 seizures. Post-SRS, seizure frequency gradually declined with a dramatic improvement in control following radiation-induced changes on MRI. Patient 1 has remained seizure-free for the past 8 months except for 2 seizures both associated with a precipitous PHT level decline (8 mcg/ml) from her baseline (18 mcg/ml). Patient 2 had the same seizure frequency until 4 months post-SRS with a gradual decline thereafter, and has remained seizure free for the past 4 months. NEUROIMAGING: Serial MRI demonstrated radiation-induced changes at 14 and 4 months in Patient 1 and Patient 2, respectively, with improvement on subsequent images. Patient 1 demonstrated a further reduction in the NAA/Cr+Cho ratio (0.276) at 2 years post-SRS (baseline=0.44) in the left hippocampus and no change on the right (baseline=0.63; post-SRS=0.648). NP TESTING: Patient 1 has had mild (not statistically significant) overall improvement compared to pre-op testing. No NP changes have been noted for Patient 2. ADVERSE EFFECTS: No unexpected post-op adverse effects except for the development of an outer right superior quadrantanopsia at 1 year post-SRS in Patient 2.
CONCLUSIONS: Preliminary results suggests that: (1) 15 Gy SRS to the MTL corresponding to proposed cATL is adequate to produce seizure remission without significant adverse effects on cognitive function; (2) radiation-induced changes noted on MRI may herald seizure remission following SRS (3) and further reduction of MRS NAA/Cr+Cho ratio may be a marker seizure remission.
(Disclosure: Salary - None, Grant - None, Equity - None, Consulting - None, Ownership - None, Materials - None, Stock - None, Royalties - None, Honoraria - None, Other - Drs. William Friedman and Frank Bova have patent in relation to LINAC stereotactic radiosurgery.)