J Neurol Surg B Skull Base 2022; 83(02): 193-202
DOI: 10.1055/s-0040-1718908
Original Article

The Effect of Prescription Isodose Variation on Tumor Control and Toxicities in Stereotactic Radiosurgery for Sporadic Vestibular Schwannoma: Propensity Score-Matched Case–Control Study

1   Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota, United States
2   Department of Radiology, Division of Radiation Oncology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
,
3   Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota, United States
,
Avital Perry
3   Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota, United States
,
Eric J. Tryggestad
4   Department of Radiation Physics, Mayo Clinic, Rochester, Minnesota, United States
,
Paul D. Brown
1   Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota, United States
,
Bruce E. Pollock
3   Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota, United States
,
Michael J. Link
3   Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota, United States
› Author Affiliations
Funding None.

Abstract

Objective Vestibular schwannoma (VS) treated with Gamma Knife stereotactic radiosurgery (SRS) was typically performed at 50% isodose line (IDL50); however, the impact of IDL variation on outcomes is poorly understood. This study aimed to compare tumor control (TC) and toxicities between treatment at 40% (IDL40) and 50% (IDL50).

Methods Sporadic/unilateral VS patients treated with SRS dose 12 to 14 Gy and prescription isodose volume ≤10cm3 were included. Propensity score matching was applied to IDL40 cohort to generate an IDL50 companion cohort, adjusting for age and prescription isodose volume. After exclusion of patients with follow-up <24 months, there were 30 and 28 patients in IDL40 and IDL50 cohorts, respectively.

Results Median follow-up time was 96 months (24–225 months). Actuarial and radiographic TC rates were 91.8% and clinical TC was 96.2% both at 5 and 10 years. TC was higher in IDL40 cohort but not significant (96.4 vs. 86.7%; p = 0.243). Hearing preservation (HP) rates were 71.9 and 39.2% at 5- and 10-year intervals, with significantly higher rates of HP noted in IDL40 cohort (83.3 vs. 57.1% at 5-year interval; 62.5 vs. 11.4% at 10-year interval; p = 0.017). Permanent facial neuropathy occurred in two patients, both from the IDL50 cohort (3.5%). Rates of post-SRS steroid treatment or shunt placement for hydrocephalus were slightly higher in IDL50 patients (6.9 vs. 17.9%; p = 0.208 and 3.3 vs. 7.1%; p = 0.532).

Conclusion For treatment of VS with SRS, dose prescription at IDL40 or IDL50 provides excellent long-term TC and toxicity profiles. IDL40 may be associated with improved long-term HP.

Note

This study was presented as a poster presentation at the 24th Annual Meeting Society for NeuroOncology, Phoenix, Arizona, November 22th to 24th, 2019.


Ethics

IRB Application number 19–002719, approval date 4/15/2019.




Publication History

Received: 05 April 2020

Accepted: 03 September 2020

Article published online:
18 February 2021

© 2021. Thieme. All rights reserved.

Georg Thieme Verlag KG
Rüdigerstraße 14, 70469 Stuttgart, Germany

 
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