Precision Radiation Treatment for Epilepsy (PRECISION)

Inclusion Criteria:

1. Age ≥ 18 years

2. Before patient registration/randomization, written informed consent must be givenaccording to ICH/GCP, and national/local regulations

3. Willingness to use contraception by a method that is deemed effective by theInvestigator during the SRT treatment and for at least 30 days following the SRTtherapy

4. The patient or caretaker is able to keep an epilepsy diary

5. The patient has a diagnosis of epilepsy established by a dedicated neurologist

6. The patient had at least 3 focal-onset seizures over a 3-month period despite two ormore antiepileptic medication trials (according ILAE Task Force on therapeuticstrategies)

7. Video electroencephalography and work-up in the epilepsy surgery working group todetermine a well-circumscribed seizure focus is available

8. Evidence (e.g. 3T-MRI or a clear SEEG delineation) of the anatomic region to betargeted with SRT, correlating with the EZ hypothesis;

9. A functional MRI to lateralize language or localize visual, motor and/or sensoryeloquent cortex has been performed in selected patients (if the lesion is expectedto be located, based on anatomy, in the language areas).

10. The patient has completed a standard battery of neuropsychological testing

11. The patient been deemed an appropriate candidate for stereotactic radiosurgery by adedicated Radiation Oncologist and Neurosurgeon/Epileptologist and referred for thestudy by one of the Dutch regional multidisciplinary epilepsy surgery working groups

12. Patients that were rejected for surgery in an earlier stage can participate in thetrial if the last change of the NVS/DBS settings were more than 1 year ago orNVS/DBS was not (yet) tried.

Exclusion Criteria:

1. Pregnancy

2. If a radiation treatment plan without exceeding the constraints for the organs atrisk is not feasible.

3. Prior cranial radiotherapy

4. If radiotherapy treatment is not possible for diverse reasons.

5. If the subject has clinically significant and uncontrolled major other medicalcondition(s) including but not limited to:

ii. psychiatric illness/social situation that would limit compliance with study requirements iii. any medical condition, with the opinion of the study investigator, places the subject at an unacceptably high risk for toxicities iv. Progressive co-morbidity which limits overall survival.