Importance of Cobalt-60 Dose Rate and Biologically Effective Dose on Local Control for Intracranial Meningiomas Treated With Stereotactic Radiosurgery

Abstract Objectives Local failure of incompletely resected vestibular schwannoma (VS) following salvage stereotactic radiosurgery (SRS) using standard doses of 12 to 13 Gy is common. We hypothesized that dose-escalated SRS, corrected for biologically effective dose, would have superior local control of high-grade VS progressing after subtotal or near-total resection compared with standard-dose SRS. Design Retrospective cohort study. Setting Tertiary academic referral center. Participants Adult patients treated with linear accelerator-based SRS for progressive VS following subtotal or near-total resection. Main Outcome Measures Dose-escalated SRS was defined by a biologically effective dose exceeding a single-fraction 13-Gy regimen. Study outcomes were local control and neurologic sequelae of SRS. Binary logistic regression was used to evaluate predictors of study outcomes. Results A total of 18 patients with progressive disease following subtotal (71%) and near-total (39%) resection of Koos grade IV disease (94%) were enrolled. Of the 18 patients, 7 were treated with dose-escalated SRS and 11 with standard-dose SRS. Over a median follow-up of 32 months after SRS, local control was 100% in the dose-escalated cohort and 91% in the standard-dose cohort (p = 0.95). Neurologic sequelae occurred in 28% of patients, including 60% of dose-escalated cohort and 40% of the standard-dose cohort (p = 0.12), although permanent neurologic sequelae were low at 6%. Conclusions Dose-escalated SRS has similar local control of recurrent VS following progression after subtotal or near-total resection and does not appear to have higher neurologic sequalae. Larger studies are needed.

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Biologically effective dose correlates with linear tumor volume changes after upfront single-fraction stereotactic radiosurgery for vestibular schwannomas

Neurosurgical Review ◽

10.1007/s10143-021-01538-w ◽

2021 ◽

Author(s):

Constantin Tuleasca ◽

Mohamed Faouzi ◽

Philippe Maeder ◽

Raphael Maire ◽

Jonathan Knisely ◽

...

Keyword(s):

Standard Deviation ◽

Effective Dose ◽

Stereotactic Radiosurgery ◽

Tumor Volume ◽

Vestibular Schwannomas ◽

Benign Tumors ◽

Biologically Effective Dose ◽

Volume Changes ◽

Single Fraction

AbstractVestibular schwannomas (VSs) are benign, slow-growing tumors. Management options include observation, surgery, and radiation. In this retrospective trial, we aimed at evaluating whether biologically effective dose (BED) plays a role in tumor volume changes after single-fraction first intention stereotactic radiosurgery (SRS) for VS. We compiled a single-institution experience (n = 159, Lausanne University Hospital, Switzerland). The indication for SRS was decided after multidisciplinary discussion. Only cases with minimum 3 years follow-up were included. The Koos grading, a reliable method for tumor classification was used. Radiosurgery was performed using Gamma Knife (GK) and a uniform marginal prescription dose of 12 Gy. Mean BED was 66.3 Gy (standard deviation 3.8, range 54.1–73.9). The mean follow-up period was 5.1 years (standard deviation 1.7, range 3–9.2). The primary outcome was changes in 3D volumes after SRS as function of BED and of integral dose received by the VS. Random-effect linear regression model showed that tumor volume significantly and linearly decreased over time with higher BED (p < 0.0001). Changes in tumor volume were also significantly associated with age, sex, number of isocenters, gradient index, and Koos grade. However, the effect of BED on tumor volume change was moderated by time after SRS and Koos grade. Lower integral doses received by the VSs were inversely correlated with BED in relationship with tumor volume changes (p < 0.0001). Six (3.4%) patients needed further intervention. For patients having uniformly received the same marginal dose prescription, higher BED linearly and significantly correlated with tumor volume changes after SRS for VSs. BED could represent a potential new treatment paradigm for patients with benign tumors, such as VSs, for attaining a desired radiobiological effect. This could further increase the efficacy and decrease the toxicity of SRS not only in benign tumors but also in other SRS indications.

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