How variations of treatment time affect the safety/efficacy of Gamma Knife (GK) radiosurgery is a matter of considerable debate. Due to the relative simplicity of treatment planning for trigeminal neuralgia (TN) this question has been addressed in a group of these patients. Using the concept of biologically effective dose (BED) the effect of the two key variables, dose and treatment time have been taken into account.METHODS A retrospective analysis was carried out on 408 TN cases, treated between 1997 and 2010. Treatment involved the use of a single 4 mm iso-center. If conditions allowed, the iso-center was placed at a median distance of 7.5 mm from the emergence of the trigeminal nerve from the brain stem. Effects were assessed in terms of the incidence of the complication, hypoesthesia, or in terms of efficacy, the incidence of 'pain free' after 30 days and at 1 and 2 years. These responses were evaluated with respect to both the physical dose and the biological effective dose (BED), the latter using a bi-exponential repair model. RESULTSRe-evaluation showed that the prescription doses, at the 100% iso-dose, varied between 75 and 97.9 Gy, delivered over 25 -135 min. The relationship between physical dose and the incidence of hypoesthesia was not significant; the overall incidence being approximately 20%. However, there was a clear relationship between BED and the incidence of hypoesthesia, the incidence increasing from < 5% after a BED of ~1800 Gy 2.47 to 42% after ~2600 Gy 2.47 . Efficacy, in terms of freedom from pain, was approximately 90%, irrespective of the BED (1550-2600 Gy 2.47 ) at 1 and 2 years. There was a suggestion from the data that 'pain free' status developed more slowly at lower BED values.CONCLUSION These results strongly suggest that safety/efficacy may be better achieved by prescribing a specific BED instead of a physical dose. A dose/time to BED conversion table has been prepared to enable iso-BED prescriptions. This finding may dramatically change dose-planning strategies in the future. This concept needs to be validated in other indications where more complex dose-planning is required.

<b><i>Background:</i></b> Radiosurgery is performed with a diversity of instruments relying usually either on a stereotactic frame or a mask for patient head fixation. Comfort and safety efficacy of the 2 systems have never been rigorously evaluated and compared. <b><i>Material and Method:</i></b> Between February 2016 and January 2017, 58 patients presenting with nonsmall cell lung cancer brain metastases have been treated by Gamma Knife radiosurgery (GKS) with random use of a frame or a mask for fixation were included patients older than 18, with &#x3c;5 brain metastases (at the exclusion of brainstem and optic pathway’s locations) and no earlier history of radiotherapy. The primary outcome measure was the pain scale assessment (PSA) at the beginning of the GKS procedure. <b><i>Results:</i></b> The PSA at the beginning of the GKS procedure was not different between the 2 groups. The PSA at the day before GKS, before magnetic resonance imaging, just after frame application, and the day after radiosurgery (departure) has shown no difference between the 2 groups. At the end of the radiosurgery itself (just after frame or mask removal) and 1 h after, the mean pain scale was higher in patients treated with the frame (<i>p</i> &#x3c; 0.05 and <i>p</i> &#x3c; 0.001, respectively) but 2 patients were not able to tolerate the mask discomfort and had to be treated with frame. Tumor control and morbidity probability were demonstrated to be no difference between the 2 groups in this population of patients with BM not in highly functional area. The median of the extra dose to the body due to the cone-beam computed tomography was 7.5 mGy with a maximum of 35 mGy in patients treated with a mask fixation (null in the others treated with frame). Mask fixation was associated to longer treatment time although the beam on time was not different between the 2 groups. <b><i>Conclusion:</i></b> In selected patients, with brain oligo-metastases out of critical location, single-dose mask-based GKS can be done with a comfort and a safety efficacy comparable to frame-based GKS. There seems to be no clear patient data that confirm the value of the mask system with regards to comfort.

Objective Epileptic patients with hypothalamic hamartoma (HH) frequently present cognitive impairments. Surgical techniques aiming at HH can be very efficient for epilepsy relief and cognitive improvement but are also demonstrated to carry a significant risk of additional reduction in memory function in these already disabled patients. Gamma knife radiosurgery (GKS) offers an efficient minimally invasive procedure. We evaluated the effect of stereotactic radiosurgery on cognitive outcome. Methods We designed a prospective single‐center case series study. Thirty‐nine epileptic patients (median age = 17 years, range = 4–50) with HH underwent preoperative and postoperative testing of intelligence quotient (IQ; all patients), including a working memory component, and other memory function testing (for patients ≥16 years old). All patients were prospectively evaluated and underwent complete presurgical and postsurgical clinical, electrophysiological, endocrinal, and visual assessments. In all patients, the postoperative assessment was performed at least 3 years after radiosurgery. We explored what variables correlate with cognitive outcome. Literature review was done for other surgical techniques and their risks for cognitive complications after surgery. Results No decline was observed in intellectual ability (including working memory) after GKS, and no memory decline was seen in adults. We observed significant improvement (>1 SD in z‐score) in working memory index (46%) and processing speed index (35%), as well as improvement in full‐scale IQ (24%), verbal comprehension index (11%), perceptual organization index (21%), verbal learning (20%), and visual learning (33%). Before GKS, the probability of seizure cessation was higher in patients with higher cognitive performance. After GKS, the cognitive improvement was significantly higher in the seizure‐free patients compared to the non‐seizure‐free patients. Significance We found clear cognitive improvement in a high percentage of patients but importantly no significant decline in intellectual ability (including working memory) and no decline in memory in adult patients 3 years after GKS. GKS compares favorably to the other surgical techniques in terms of cognitive outcome, with similar seizure freedom.