Usami and colleagues4 from the University of Tokyo provide data on 7 patients who underwent Gamma Knife surgery (GKS) for mesial temporal lobe epilepsy (MTLE) between 1996 and 1999. Five of the 7 patients received a maximum radiosurgery dose of 50 Gy, which led to significant reduction in seizures in all 4 patients who underwent follow-up. However, 2 had signs of adverse radiation effects, and resection was later performed 5 and 10 years later. The authors caution, “...the risk of [symptomatic radiation necrosis] should be considered when the clinical significance of this treatment is evaluated.” Currently, there is interest in epilepsy radiosurgery as an alternative to microsurgical resection for MTLE. A multicenter randomized trial, in which I am a participating investigator, comparing radiosurgery with resection is being performed under the leadership of Drs. Nicholas Barbaro and Mark Quigg. First, it is interesting that these cases were even performed by Usami and colleagues in the way in which they were. Epilepsy radiosurgery was still being performed in animal models in the 1990s and even into the early part of the past decade.2,3 Results on the biology of these radiosurgical effects were still coming out prior to the first National Institutes of Health–sponsored trial in the US, which was completed just a few years ago.1 As the authors describe, radiation injury is related to numerous factors, of which dose and volume (in addition to location and other patient characteristics) are paramount. To summarize, the patients underwent early generation dose planning using the Kula system for which image integration was not possible and had rather excessive target volumes, and large collimators (18 mm) were used. Dose planning without image integration (the isodose lines were not directly shown on a brain image) was performed in Cases 1–4 and with image integration in Cases 5–7. It is important to note that in the National Institutes of Health–sponsored trial,1 all centers had to create a target volume between 5.5 and 7.5 cm3. The target volumes in this experience in Cases 3, 4, and 5 were 12, 7.8, and 8.3 ml, respectively. Within the protocol of the ongoing Radiosurgery or Open Surgery for Epilepsy (ROSE) trial, dose planning is challenging even with sophisticated software. Multiple isocenters are necessary, customized beam blocking is used to minimize the dose to the optic tract and brainstem, and the target volume must be within defined limits. Radiation effects, when they occur, can appear as heterogeneous entities. The figure shown for Case 4 notes a “cavernous malformation,” although it is not clear why this diagnosis was made. There are certainly imaging-defined changes, and the eventual pathology, as noted in the report itself, did not disclose a cavernous malformation. The authors conclude, “Currently, the indications for consideration of GKS as an alternative to surgery are limited to a few cases that may be inoperable.” Given the fact that such procedures were performed more than 10 years ago using fairly crude techniques, I do not think that this conclusion is appropriate in 2012. After these patients were treated, controlled multicenter trials were conducted on epilepsy radiosurgery that led to funding of a large multicenter and multinational randomized trial to compare radiosurgery with resection for MTLE. The scope of this study is unprecedented and will be very important. Using current techniques, the results of radiosurgery and resection appear similar, and we encourage all those involved in the management of these patients to contribute patients to the ROSE trial. (http://thejns.org/doi/abs/10.3171/2011.12.JNS112119)