Purpose: Accurate target volume definition is essential for precision stereotactic radiosurgery (SRS). MRI is widely used in conjunction with CT to provide the necessary softâ€?tissue delineation. In the era of MRI-guided radiotherapy, the use of multiparametric quantitative MR imaging allows modification of radiation therapy, and customization of treatment based on an individual patient's prognosis or early response to treatment. The only drawbacks of this procedure are longer scanning times with resultant degradation of image quality due to patient movement during simulation or online treatment at an MR-Linac machine. Strategically acquired gradient echo (STAGE) imaging was optimized in this project for use in MRI-only SRS planning.
Methods: We finalized MRI-only SRS planning for frameless patients using MRI-compatible Type S overlay (CIVCO) on an Aera 1.5T Siemens RT edition. Protocol: 1) field map (1 minute)â€”geometric correction; 2) T1 MPRAGE (5 min)â€”Anatomical and planning; 3) Synthetic CT sequences (6 minutes)â€”planning; 4) STAGE pre-contrastâ€”generate T1-weighted, T1 map, T2-weighted, PD map, PD weighted, susceptibility weighted imaging (SWI), quantitative susceptibility mapping (QSM), T2*, R2*, FLAIR (10 minutes); 5) STAGE post-contrast Gd (4 min)â€”vascular imaging, simultaneous magnetic resonance angiography and venography (MRAV)â€”(total scanning time 26 minutes).
Results: STAGE pre- and post-processing to generate quantitative and vascular MR images provides substantial information regarding tumor location, surroundings, and extent, which improves tumor segmentation and renders more precise treatment planning.
Conclusion: We initially optimized the protocol on one healthy volunteer and five patients. Our neuroradiologic and radiation oncology team will help us further study these cases retrospectively and correlate the new tumor regions with SRS patient outcomes.