Re-Evaluation of the Size Limitation in Single-Session Stereotactic Radiosurgery for Brain Arteriovenous Malformations: Detailed Analyses on the Outcomes with Focusing on Radiosurgical Doses

Abstract

BACKGROUND Single-session stereotactic radiosurgery (SRS) for large arteriovenous malformations (AVMs) ≥10 mL remains controversial, which is considered as the current size limitation. OBJECTIVE To reconsider the size limitation of SRS for AVMs by profoundly analyzing dose-volume relationship. METHODS Data on 610 consecutive patients with AVM treated with SRS using regular (18-22 Gy) or low (<18 Gy) prescription doses were retrospectively analyzed. AVMs were classified into 4 groups: small (<5 mL), medium (≥5 and <10 mL), medium-large (≥10 and <15 mL), and large (≥15 mL). The maximum volumes were 22.5 mL (regular-dose group) and 23.5 mL (low-dose group). RESULTS When treated with regular doses, the cumulative 6-yr obliteration rates for each of the 4 AVM groups were 86%, 80%, 87%, and 79%, respectively; the cumulative 10-yr significant neurological event (SNE) rates were 2.6%, 3.9%, 6.8%, and 5.3%, respectively. Regarding large AVMs, regular-dose SRS resulted in marginally better obliteration rate (6-yr cumulative rate, 79% vs 48%, P = .111) and significantly lower SNE (5-yr cumulative rate, 5% vs 31%, P = .038) and post-SRS hemorrhage rate (8-yr cumulative rate, 0% vs 54%, P = .002) compared to low-dose SRS. Multivariate analyses revealed that regular-dose SRS significantly contributed to increase in the obliteration rate and decrease in SNEs and hemorrhage. CONCLUSION The outcomes for large AVMs were generally favorable when treated with ablative doses. Single-session SRS could be acceptable for AVMs up to ≈20 mL if treated with ablative doses.

The factors associated with obliteration following stereotactic radiosurgery in patients with brain arteriovenous malformations: a meta‐analysis

“…Benefits of embolization prior to SRS included reduced AVM volume allowing application of higher marginal dose and occlusion of associated aneurysms with a higher risk of bleeding. However, it also possibly results in some adverse effects like delayed recanalization and obscure nidus delineation 6,15 . Our analysis suggested that it was an independent factor reducing the nidus obliteration rate with an HR of 0.65, indicating that the probability of obliteration was dropped by 35% for AVMs who were previously embolized before SRS and consistent with a previous meta‐analysis investigating the efficacy of SRS in embolized AVMs 24 .…”

“…Pooled estimates showed no significant and independent correlation between male sex and total obliteration by univariate analysis based on five studies (Fig. 3(a)), and by multivariate analysis based on two papers 6,16 . Regarding patient age, according to nine articles involving 3489 subjects with the median/mean age ranging from 22 to 42, no significant relationship between age and AVM obliteration was shown with univariate analysis (Fig.…”

“…Higher marginal dose was shown to have a significant and independent relationship with an increased probability of AVM obliteration. Furthermore, in event of a higher marginal dose defined as ≥17–18 Gy, it was shown to be more significantly associated with an increased probability of obliteration on both univariate (three studies 6,12,18 ) and multivariate analysis (two studies 6,18 ). Besides, based on three studies 5,11,14 higher SRS maximal dose was found to have a slightly significant association with AVM obliteration but failed to be an independent factor on multivariate analysis.…”

“…Seven studies contributed data to the analysis of prior embolization, two 6,17 of which also evaluated prior surgery as an associated factor. On the basis of 717 AVM patients (18.5%) treated with at least one embolization procedure before SRS, overall results showed no significant association between pre‐SRS embolization and total closure probability on univariate analysis (Fig.…”

<p>Gamma Knife Radiosurgery For Brain Vascular Malformations: Current Evidence And Future Tasks</p>

“…Large AVMs are challenging targets. Radiosurgical doses are generally reduced for fear of RAEs, which in turn could decrease the obliteration rate and might eventually result in a higher hemorrhage rate 80. In short, it is important to balance the therapeutic effect and risks.…”