To the Editor: We thank the authors, Zengpanpan Ye, Xiaolin Ai, and Chao You, for their interest in our paper.1 We agree with Ye et al2 that there is likely some degree of overlap among the 755 patients in the Kano et al 20173 study of adverse radiation effects (ARE) after stereotactic radiosurgery (SRS) for brain arteriovenous malformations (AVM) and the 157 pediatric patients in the Kano et al 20124 study of SRS for pediatric AVM patients. Of note, whereas the recent 2017 study only included patients with at least 2 yr of follow-up, the minimum follow-up in the earlier 2012 study was 6 mo. Therefore, not all of the patients in the 2012 study of pediatric AVMs were included in the 2017 study of post-SRS ARE in AVM patients. However, according to our inclusion criteria, only the former study should have been included. Figure. View largeDownload slide Meta-analysis of the association of superficial versus deep location with the development of permanent RIC. A, The overall findings and B, individual study findings are shown. Figure. View largeDownload slide Meta-analysis of the association of superficial versus deep location with the development of permanent RIC. A, The overall findings and B, individual study findings are shown. The association between deep location and permanent radiation-induced changes (RIC) was not assessed in our meta-analysis.1 Herein, we provide the results of this meta-analysis using identical methods (Figure). Compared to Ye et al,2 we found 6 overlapping studies and 1 new study, and we excluded 1 study.3,5-11 Moreno-Jiménez et al11 was excluded from the meta-analysis, since the total number of superficial and deep AVMs could not be extracted. In this study, parietal, occipital, intraventricular, corpus callosum, and cerebellar AVMs were grouped together (n = 12). Ye et al2 appeared to have included all of these AVMs in the superficial group in their analysis. Additionally, the ‘Other location’ and ‘Deep location’ column headings in their figure appear to be reversed. As we noted in our methods, lobar and cerebellar AVMs were considered superficial, whereas corpus callosum, basal ganglia, thalamic, periventricular, and brainstem AVMs were considered deep.1 We found that deep AVM location was significantly associated with permanent RIC (odds ratio = 3.13, 95% confidence interval: 1.69-5.80; P = .0003). We believe that the discrepancies between the findings of Ye et al2 and our own1 likely relate to different classifications of AVM locations. We agree with Ye et al2 that the Hanakita et al 201512 study was misclassified as a ‘USA’ study, whereas it should have been reported as a ‘Not USA’ study. Furthermore, the authors note that 18.2% of patients in the Parkhutik et al13 2013 study underwent repeat SRS. Unfortunately, the numbers of patients who developed radiological, symptomatic, and permanent RIC after initial vs repeat SRS were not delineated. Regarding the point about single-session vs second SRS, Ye et al2 seem to be confused on terminology. Single-session SRS is delivered in 1 fraction, as compared to hypofractioned SRS, which is delivered in 2-5 fractions. This may be true, regardless of whether a patient underwent 1 or more than 1 SRS procedures at discrete periods of intervention. As with this study, the lack of granularity and the absence of individual patient data are critical limitations of systematic reviews and meta-analyses. This limitation must be weighed against the primary advantage of this type of study, which is the inclusion of a large number of patients. This lack of individual patient data encountered by systematic reviews and meta-analyses can be partially overcome by multicenter cohort studies and prospective registries.14,15 With respect to ARE after AVM SRS, a multicenter study regarding this topic is currently underway through the auspices of the International Gamma Knife Research Foundation. We hope that similar multicenter studies will be undertaken by our colleagues in China. In summary, the aforementioned changes do not substantially impact the findings of our study. After excluding the Kano et al 2012 study,4 the updated rates of radiological, symptomatic, and permanent RIC are 35.5% (1143/3222 patients), 9.9% (491/4956 patients), and 3.9% (200/5072 patients), respectively.4 Deep AVMs are significantly more likely than superficial lesions to have both symptomatic and permanent RIC. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Ilyas A, Chen C-J, Ding D et al. Radiation-induced changes after stereotactic radiosurgery for brain arteriovenous malformations: a systematic review and meta-analysis. Neurosurgery . 2017. published online ahead of print: October 13, 2017 (doi: 10.103/neuros/nyx502). 2. Zengpanpan Y, Xiaolin A, Chao Y. Letter: radiation-induced changes after stereotactic radiosurgery for brain arteriovenous malformations. Neurosurgery . 2017; 82( 3): E75- E76. 3. Kano H, Flickinger JC, Tonetti D et al. Estimating the risks of adverse radiation effects after gamma knife radiosurgery for arteriovenous malformations. Stroke . 2017; 48( 1): 84- 90. Google Scholar CrossRef Search ADS PubMed 4. Kano H, Kondziolka D, Flickinger JC et al. Stereotactic radiosurgery for arteriovenous malformations, Part 2: management of pediatric patients. J Neurosurg Pediatr . 2012; 9( 1): 1- 10. Google Scholar CrossRef Search ADS PubMed 5. Pollock BE, Link MJ, Stafford SL, Garces YI, Foote RL. Stereotactic radiosurgery for arteriovenous malformations. Neurosurgery . 2016; 78( 4): 499- 509. Google Scholar CrossRef Search ADS PubMed 6. Nagy G, Grainger A, Hodgson TJ et al. Staged-volume radiosurgery of large arteriovenous malformations improves outcome by reducing the rate of adverse radiation effects. Neurosurgery . 2017; 80( 2): 180- 192. Google Scholar PubMed 7. Matsuo T, Kamada K, Izumo T, Hayashi N, Nagata I. Linear accelerator-based radiosurgery alone for arteriovenous malformation: more than 12 years of observation. Int J Radiat Oncol Biol Phys . 2014; 89( 3): 576- 583. Google Scholar CrossRef Search ADS PubMed 8. Maity A, Shu HKG, Tan JE et al. Treatment of pediatric intracranial arteriovenous malformations with linear-accelerator-based stereotactic radiosurgery: The University of Pennsylvania experience. Pediatr Neurosurg . 2004; 40( 5): 207- 214. Google Scholar CrossRef Search ADS PubMed 9. Hanakita S, Shin M, Koga T, Igaki H, Saito N. Outcomes of volume-staged radiosurgery for cerebral arteriovenous malformations larger than 20 cm(3) with more than 3 years of follow-up. World Neurosurg . 2016; 87: 242- 249. Google Scholar CrossRef Search ADS PubMed 10. Buis DR, Meijer OWM, Van Den Berg R et al. Clinical outcome after repeated radiosurgery for brain arteriovenous malformations. Radiother Oncol . 2010; 95( 2): 250- 256. Google Scholar CrossRef Search ADS PubMed 11. Moreno-Jiménez S, Celis MA, Lárraga-Gutiérrez JM, de Jesús Suárez-Campos J, García-Garduño A, Hernández-Bojórquez M. Intracranial arteriovenous malformations treated with linear accelerator based conformal radiosurgery: clinical outcome and prediction of obliteration. Surg Neurol . 2007; 67( 5): 487- 491. Google Scholar CrossRef Search ADS PubMed 12. Hanakita S, Koga T, Shin M, Igaki H, Saito N. The long-term outcomes of radiosurgery for arteriovenous malformations in pediatric and adolescent populations. J Neurosurg Pediatr . 2015; 16( 2): 1- 10. Google Scholar CrossRef Search ADS PubMed 13. Parkhutik V, Lago A, Aparici F et al. Late clinical and radiological complications of stereotactical radiosurgery of arteriovenous malformations of the brain. Neuroradiology . 2013; 55( 4): 405- 412. Google Scholar CrossRef Search ADS PubMed 14. Sheehan JP, Kavanagh BD, Asher A, Harbaugh RE. Inception of a national multidisciplinary registry for stereotactic radiosurgery. J Neurosurg . 2016; 124( 1): 155- 162. Google Scholar CrossRef Search ADS PubMed 15. Starke RM, Kano H, Ding D et al. Stereotactic radiosurgery for cerebral arteriovenous malformations: evaluation of long-term outcomes in a multicenter cohort. J Neurosurg . 2017; 126( 1): 36- 44. Google Scholar CrossRef Search ADS PubMed Copyright © 2017 by the Congress of Neurological Surgeons
Neurosurgery – Oxford University Press
Published: Mar 1, 2018
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