Evaluating stereotactic accuracy with patient-specific MRI distortion corrections for frame-based radiosurgery.

Abstract

This study examines how MRI distortions affect frame-based SRS treatments and assesses the need for clinical distortion corrections. The study included 18 patients with 80 total brain targets treated using frame-based radiosurgery. Distortion within patients' MRIs were corrected using Cranial Distortion Correction (CDC) software, which utilizes the patient's CT to alter planning MRIs to reduce inherent intra-cranial distortion. Distortion was evaluated by comparing the original planning target volumes (PTVORIG) to targets contoured on corrected MRIs (PTVCORR). To provide an internal control, targets were also re-contoured on uncorrected (PTVRECON) MRIs. Additional analysis was done to assess if 1mm expansions to PTVORIG targets would compensate for patient-specific distortions. Changes in target volumes, DICE and JACCARD similarity coefficients, minimum PTV dose (Dmin), dose to 95% of the PTV (D95%), and normal tissue receiving 12Gy (V12Gy), 10Gy (V10Gy), and 5Gy (V5Gy) were calculated and evaluated. Student's t-tests were used to determine if changes in PTVCORR were significantly different than intra-contouring variability quantified by PTVRECON. PTVRECON and PTVCORR relative changes in volume were 6.19%±10.95% and 1.48%±32.92%. PTVRECON and PTVCORR similarity coefficients were 0.90±0.08 and 0.73±0.16 for DICE and 0.82±0.12 and 0.60±0.18 for JACCARD. PTVRECON and PTVCORR changes in Dmin were -0.88%±8.77% and -12.9±17.3%. PTVRECON and PTVCORR changes in D95% were -0.34%±5.89 and -8.68%±13.21%. The 1mm expanded PTVORIG targets did not entirely cover 14 of the 80 PTVCORR targets. Normal tissue changes (V12Gy, V10Gy, V5Gy) calculated with PTVRECON were (-0.09%±7.39%, -0.38%±5.67%, -0.08%±2.04%) and PTVCORR were (-2.14%±7.34%, -1.42%±5.45%, -0.61%±1.93%). Except for V10Gy, all PTVCORR changes were significantly different (p<0.05) than PTVRECON. MRIs used for SRS target delineation exhibit notable geometric distortions that may compromise optimal dosimetric accuracy. A uniform 1mm expansion may result in geometric misses; however, the CDC algorithm provides a feasible solution for rectifying distortions, thereby enhancing treatment precision.