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MO_7_2641 - Stereotactic Radiosurgery for Vestibular Schwannoma: Longitudinal Radiographic Outcomes Single and Fractionated Treatments.

Monday, October 22
10:45 AM - 12:15 PM
Location: Innovation Hub, Exhibit Hall 3

Stereotactic Radiosurgery for Vestibular Schwannoma: Longitudinal Radiographic Outcomes Single and Fractionated Treatments.
M. H. Khattab1, D. M. Wharton2, E. Kim3, L. B. Chambless4, K. Weaver4, G. Luo3, A. Yock3, M. Morales2, A. Attia2, and A. J. Cmelak2; 1Vanderbilt University Medical center, Nashville, TN, 2Department of Radiation Oncology, Vanderbilt University Medical Center, Nashville, TN, 3Vanderbilt University Medical Center, Nashville, TN, 4Department of Neurosurgery, Vanderbilt University Medical Center, Nashville, TN

Purpose/Objective(s): Vestibular schwannomas (VS) are treated with fractionated stereotactic radiosurgery (SRS) to attempt hearing preservation. There are no established predictors of longitudinal effect on tumor volume, pseudoprogression or necrosis.

Materials/Methods: An IRB approved retrospective review of patients treated with 1, 3, or 5 fraction (fx) SRS for VS at our institution from 1998-2016, with at least 2 years of follow-up was performed. Radiographic follow-up by MRI was used to calculate tumor volume based on tridimensional measurements and non-spherical tumor volume was approximated by pi/6*x*y*z. Radiologic responders were those with reduction by at least 2mm in any dimension. Radiologic non-responders had no growth or reduction. Treatment failures grew at least 2mm in any dimension by last follow-up. Pseudoprogression was defined as any interval increase in tumor volume that later normalized or reduced to below baseline tumor volume.

Results: A total of 56 patients met selection criteria. Most patients were treated with 5 fractions (32, 57%), then 3 fractions (12, 21%) and 1 fraction (12, 21%). The most common dose and fractionation regimens were 1250 cGy x 1 (7, 12.5%), 700 cGy x 3 (12, 21.4%), 500 cGy x 5 (12, 21.4%), and 450 cGy x 5 (14, 25%). Patients treated with 1 fx had a median baseline tumor volume of 1.2 cc (range 0.04-3.88), median dose 1250 cGy per fx (range 1200-1600), and median percent reduction in tumor volume of 2.7 % (range -396 to 85). Patients treated with 3 fxs had a median baseline tumor volume of 1.2 cc (range 0.4-7.7), median dose of 700 cGy (range 700-700), and a median percent reduction in tumor volume of 24 % (range -272 to 92). Patients treated with 5 fxs had a median baseline tumor volume of 2.0 cc (range 0.07-7.49), median dose of 450 cGy (range 400-550), and a median percent reduction in tumor volume of 6 % (range -290 to 89). Regardless of the number of fxs, patients had similar rates of pseudoprogression (25% in single, 33% in 3 fx and 31% in 5 fx cohorts). Patients treated with 3 fxs had lower rates of radiographic necrosis (58% with 3 fx vs 75% with 1 or 5 fx) but higher rates of radiologic response (67% with 3 fx vs 33% with 1 fx or 44% with 5 fx) and lower rates of radiologic non-response (17% with 3 fx vs 58% with 1 fx or 38% with 5 fx). Patients with more fxs had higher rates of treatment failure (8% with 1 fx vs 17% with 3 fx or 19% with 5 fx).

Conclusion: SRS with 1, 3, or 5 fxs was safe and effective in reducing tumor volume of VS. About one-third of all patients had evidence of pseudoprogression. Patients treated with 3 fx SRS had the largest % reduction in tumor volume (median 24%) and lowest rates of necrosis.

Author Disclosure: M.H. Khattab: None. E. Kim: None. L.B. Chambless: Consultant; National Football League. K. Weaver: None. A. Yock: None. M. Morales: None. A. Attia: Employee; Vanderbilt University. Honoraria; Brainlab, qfix. Advisory Board; AstraZeneca. Travel Expenses; qfix. Director of Radiosurgery Program; Vanderbilt University. Nashville Volunteer Leadership Board Member; American Cancer Society.

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