Novel Application of PSMA-PET CT in the Evaluation and Management of Vestibular Schwannomas

Summary: Vestibular schwannomas (VS) are benign tumors originating from vestibulocochlear nerve Schwann cells. Contrast-enhanced MRI (CEMRI) is the gold standard for initial evaluation, monitoring, and post-treatment assessment. Treatment options include observation, stereotactic radiosurgery, fractionated radiation therapy, or microsurgery, with intervention typically prompted by rapid tumor growth and worsening symptoms. However, reliable clinical parameters to predict tumor growth or future intervention needs are lacking, and MRI may have limitations differentiating between residual/recurrent tumors and post-treatment changes. Prostate Specific Membrane Antigen (PSMA), originally found in prostatic tissue, is also expressed in VS. We report the first clinical application of 68Ga-PSMA PET-CT as an adjunct imaging modality in VS management. Ten patients with 11 VS underwent 68Ga-PSMA PET-CT. All but one patient, who could not have an MRI due to an implant, also had CEMRIs for initial or post-treatment evaluation. PSMA PET avidity was quantified using maximum standardized uptake values (SUVmax) for the tumor and the superior sagittal sinus (SSS) as a cranial blood pool reference. PET data were analyzed using tumor SUVmax and the tumor to SSS SUVmax ratio (SUVRsss). The The Pearson correlation coefficient determined correlation, and intergroup comparisons with statistical significance were assessed using the Mann-Whitney test. All patients had unilateral schwannomas, except one with bilateral tumors. Before undergoing PSMA PET-CT one patient underwent surgery, while another had surgery followed by radiation. Eight treatment-naïve patients had PSMA PET-CT for treatment decision-making and planning; among them, 3 received fractionated stereotactic radiation (SRT), 2 underwent surgery, and 3 chose a wait-and-scan approach. Treated tumors (n=5) versus those under observation (n=4) mean SUVmax and SUVRsss were 3.1 vs. 0.6 (p=0.014) and 2.1 vs. 0.5 (p=0.027). Tumor size (R = 0.899; p < 0.001) and Koos grade (R = 0.821; p = 0.007) showed strong correlations with SUVmax and SUVRsss. Follow-up PET, about a year later, revealed stable to slightly decreased SUVmax (3.5 to 3.2 and 1.8 to 1.3) for 2 patients who had SRT after baseline PET and for one patient with prior surgery and radiation (4.4 to 3.3) before having baseline PET. In a patient with bilateral AS, the growing larger tumor (1.8 cm) had higher SUVmax (1.36) compared to the smaller non-growing tumor (0.3 cm) which showed no visible avidity. PSMA PET-CT aided in SRT planning alongside CEMRI when available, and for one patient unable to have an MRI, PSMA PET-CT facilitated tumor delineation for SRT planning. Larger vestibular schwannomas (VS) showed significantly higher avidity on PSMA PET than smaller tumors, with SUVmax ≥ 1.5 and SUVRsss ratios > 1 linked to a greater likelihood of treatment. PSMA PET may serve as a valuable adjunct in VS management, warranting further prospective studies to clarify its role. Pavnesh Kumar, MD (Presenting Author) - The Arthur G. James Cancer Hospital and Richard J. Solove Research Institute, The Ohio State University Wexner Medical Ctr.; Rituraj Upadhyay, MD (Co-Author) - The Ohio State University; Kyle C.. Wu, MD (Co-Author) - The Ohio State University; Daniel Prevedello, MD (Co-Author) - The Ohio State University; Edward Dodson, MD (Co-Author) - The Ohio State University; Divya Yadav, MD (Co-Author) - Weill-Cornell Medical Center; Jonathan Kinsely, MD (Co-Author) - Weil Cornell Medical Center; Oliver Adunka, MD (Co-Author) - The Ohio State University; Evan Thomas (he/him/his), MD, PhD (Co-Author) - The Ohio State University; Raju Raval (he/him/his), MD, DPhil (Co-Author) - The Ohio State University; Sasha Beyer (she/her/hers), MD, PhD (Co-Author) - The Ohio State University; Bingfeng Tang, MD (Co-Author) - The Ohio State University; Jana Ivanidze, MD, PhD (Co-Author) - Weill-Cornell Medical Center; Joshua D.. Palmer, MD (Co-Author) - Department of Radiation Oncology, The James Cancer Hospital and Solove Research Institute at The Ohio State University Wexner Medical Center