Radiomic Feature Changes in Adrenal Lesions Treated With MR-Guided Stereotactic Body Radiation Therapy

Abstract

Magnetic resonance image guided stereotactic body radiotherapy (MRgSBRT) is an advanced technology that may provide radiomic feature changes during treatment of adrenal lesions feasible for adaptation.A prospectively maintained database was retrospectively reviewed for 24 patients with adrenal lesions who underwent MRgSBRT. Histogram features (n = 7, Table 1) were extracted from MRgSBRT images (TRueFISP sequence, 1.5mm/3mm voxel size/slice thickness) from adrenal malignancy patients scanned at simulation (SIM) approximately 14 days before SBRT start, and prior to each of 5 daily fractions (F1-F5) of 8-12 Gy to Gross Tumor Volume (GTV). Tumor ROI was derived by 3mm radial erosion of GTV in 3D. Each scan was divided by median intensity in kidney for image normalization. Significance of changes SIM-F1 and F1-F5 were assessed using two-sided paired t-test. Response to treatment was assessed via follow up CT scan roughly 3 months after MRgSBRT via RECIST v1.1, with overall response rate (ORR) including complete and partial response. Radiomics features were tested for association with clinical variables using the Kruskal-Wallis test.Patients had a median age of 67 years (19-80). The majority of adrenal lesions were metastatic sites (88%), while there were 2 patients with primary adrenocortical carcinoma and 1 patient with pheochromocytoma. All patients were treated with MRgSBRT in 5 fractions to a median dose of 50 Gy (40-60). Of 23 evaluable cases, rates of complete response (CR), partial response (PR), and stable disease (SD) were 13%, 35%, and 52%, respectively. Median follow up was 9.7 months (1-22). Significant changes in MRgSBRT of the tumors were observed after treatment (F1-F5, Table 1) with an increase in image signal median and interquartile range (IQR) consistent with radiation response. No signal changes were seen prior to treatment (SIM-F1). Erosion of GTV to remove tissue borders was required to observe the changes F1-F5 (P = 0.08 median,0.67 IQR for full GTV volume). For association to outcome considering varying dose per fraction, signal ratios were calculated between F1 and fraction closest to 40 Gy cumulative dose. There was a significant relationship between IQR ratio and ORR (CR/PR cases: mean 0.94 ± 0.03, SD cases: mean 1.11 ± 0.06, P = 0.011).Significant increases in image signal median and IQR were identified in patients with adrenal lesions undergoing MRgSBRT, consistent with radiation response. MRgSBRT radiomic feature changes may allow for better personalization of radiotherapy going forward.