RESUMO
AIMS: To compare the accuracy of nidus delineation using magnetic resonance angiography (MRA) to digital subtraction angiography (DSA) and to evaluate setup accuracy of non-invasive frame SRS treatments. SETTINGS AND DESIGN: A prospective observational study of 16 patients who underwent non-invasive frame LINAC-based SRS for brain AVMs. MATERIALS AND METHODS: The nidus was separately delineated using DSA and MRA after co-registration onto CT simulation images and compared with respect to their volume and maximum diameters. During treatment, the setup errors observed in x-, y-, and z-directions were recorded. STATISTICAL ANALYSIS: Paired t-test (to compare volume and maximum diameter). Wilcoxon signed-rank test (for setup accuracy). RESULTS: The mean volume of nidus contoured in MRA was 4.16 cc compared to 3.11 cc in DSA (P 0.297). The mean maximum diameters using MRA and DSA, respectively, in antro-posterior, cranio- caudal, and transverse diameters were 21.97 cc vs. 19.46 cc (P 0.2380), 6.59 cc vs. 9.63 cc (P 0.161), and 18.87 cc vs. 16.81 cc (P 0.178). But these modalities can potentially misinterpret the nidus volume, warranting caution for use of either modality alone. The mean translational shift observed in the x-, y-, and z-directions were 0.06 mm, 0.13 mm, and 0.13 mm, respectively, when couch was brought to neutral position after clockwise couch rotation and 0.07, 0, and 0, respectively, after counterclockwise couch rotation. CONCLUSION: This study could not demonstrate any statistically significant differences in nidus delineation between MRA and DSA. Setup accuracy achieved with non-invasive thermoplastic mask-based immobilization is within acceptable limits for SRS.