Abstract
Leksell stereotactic radiosurgery is an effective option for patients with vestibular schwannomas. Some centers use a combination of stereotactic CT fused with stereotactic MR imaging to achieve an optimal target definition as well as minimize the radiation dose delivered to adjacent structures that correlate with hearing outcomes. The present prospective study was designed to determine whether there is cochlear dose variability between MR imaging and CT. Fifty consecutive patients underwent stereotactic radiosurgery for vestibular schwannomas. Dose-planning was performed using high-definition fused stereotactic MR imaging and stereotactic CT images. The 3D cochlear volume was determined by delineating the cochlea on both CT and T2-weighted MR imaging. The mean radiation dose, maximum dose, and 3- and 4.20-Gy cochlear volumes were identified using standard Leksell Gamma Knife software. The median mean radiation dose delivered to the cochlea was 3.50 Gy (range, 1.20-6.80 Gy) on CT and 3.40 Gy (range, 1-6.70 Gy) on MR imaging (concordance correlation coefficient = 0.86, r 2 = 0.9, P ≤ .001). The median maximum dose delivered to the cochlea was 6.7 Gy on CT and 6.6 Gy on MR imaging (concordance correlation coefficient = 0.89, r 2 = 0.90, P ≤ .001). Dose-volume histograms generated from CT and MR imaging demonstrated a strong level of correlation in estimating the 3- and 4.20-Gy volumes (concordance correlation coefficient = 0.81, r 2 = 0.82, P ≤ .001 and concordance correlation coefficient = 0.87, r 2 = 0.89, P ≤ .001). Both MR imaging and CT provide similar cochlear dose parameters. Despite the reported superiority of CT in identifying bony structures, high-definition MR imaging alone is sufficient to identify the radiation doses delivered to the cochlea.
Highlights
BACKGROUND AND PURPOSELeksell stereotactic radiosurgery is an effective option for patients with vestibular schwannomas
Dose-volume histograms generated from CT and MR imaging demonstrated a strong level of correlation in estimating the 3- and 4.20-Gy volumes
Vestibular schwannomas (VS), known as acoustic neuromas, are benign tumors that most commonly arise from the vestibular portion of cranial nerve VIII, the vestibulocochlear nerve
Summary
Fifty consecutive patients underwent stereotactic radiosurgery for vestibular schwannomas. The 3D cochlear volume was determined by delineating the cochlea on both CT and T2-weighted MR imaging. Patient Population Between May 2016 and October 2017, fifty consecutive patients with VS underwent MR imaging and CT-guided SRS at the University of Pittsburgh Medical Center. There were 26 men and 24 women with a median age of 60 years (range, 28 –77 years) at the time of SRS. The median duration of symptoms before SRS was 18 months. The median speech discrimination score and puretone average at the time of SRS were 64% and 37 dB, respectively. Hearing level was classified as Gardner Robertson grades I and II in 32 patients (64%). SRS was the primary management in 46 patients (92%). Three patients had SRS for residual tumor after surgery, and 1 patient, for recurrent tumor after prior SRS
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