The Potential Use of Radiomics With Pre-radiation Therapy MR Imaging in Predicting Risk of Pseudoprogression in Glioblastoma Patients

Abstract

progressed following initial treatment with SRS. The purpose of this project is to report the outcome of our repeat SRS series. Materials/Methods: A total of 6 patients were treated with repeat SRS at our institution between 1993 and 2019. We excluded patients with bilateral disease at presentation or neurofibromatosis. All patients were required to have undergone magnetic resonance (MR) planning for both SRS treatments. DVH analysis was performed on the tumor and critical structures. Toxicity was assessed per CTCAE grading. All SRS treatments were delivered with a Linac system using head frame immobilization with the dose prescribed to the 70% or 80% isodose covering the periphery of the visible tumor on MR scan. The prescribed dose was 12.5 Gy in all initial and repeat SRS treatments with the exception of one repeat treatment that was 10 Gy. The average GTV volume was larger during repeat treatment than initial treatment (3.8 cc vs 1.9 cc). In addition to being larger tumors, tumors during repeat treatment had higher average touching distance with the brainstem (15.0 mm vs 6.7 mm) and more brainstem compression (2.8 mm vs 0.3 mm). Results: Follow-up with MR scan following the second SRS treatment was a median 3.9 years (range, 0.9-8.7 years). A second SRS treatment resulted in a tumor control rate (lack of progression) of 83% (5/6). The one patient who progressed after repeat SRS subsequently underwent surgical resection and is alive. Actuarial rates at 10 years following repeat SRS were as follows: tumor control, 80%; absolute survival, 80%; and cause-specific survival, 100%. Of the patients with at least minimal hearing retention prior to initial SRS, none had ipsilateral hearing preservation after initial radiation treatment. Improvement in any pretreatment cranial nerve deficits was not seen. The only permanent grade 3 toxicity from repeat SRS was a single case of V2 deficit. No patient developed a stroke, malignant transformation, induced second tumor, or facial nerve deficit. Conclusion: Repeat single fraction SRS as delivered in our series is an excellent treatment option for vestibular schwannoma that has progressed following initial treatment with SRS.