Room: Exhibit Hall | Forum 2
Purpose: Stereotactic ablative body radiotherapy (SABR) for renal cell carcinoma (RCC) requires high fidelity of renal motion information for treatment planning and guidance. Respiratory-induced renal displacement has been investigated using 4D-CT and MRI, while renal velocity is hardly investigated due to the imaging technique limitations. We aimed to quantify respiratory-induced kidney motion velocity using a sub-second-rate fast 3D+t MRI technique.
Methods: Nine volunteers (34.33Â±5.77 years) underwent supine free-breathing 1.5T abdominal MRI using a CAIPIRINHA-VIBE sequence (transverse, 615ms/frame, slices-in-volume=56, voxel size: 2.7x2.7x4mm, frames=144 (maximum restricted by console), acquisition-time=89s). Respiratory profile was recorded using a pressure bellow. Kidney VOIs were drawn on the reference 2nd frame images. Following frames were rigidly registered to the reference. 3D renal motion velocity was calculated and analyzed in both kidneys.
Results: Substantial inter-subject difference was observed in volumetric left/right kidney motion displacement (range: 7.58Â±0.97/7.31Â±1.22mm to 16.61Â±2.86/17.05Â±2.56mm) and velocity (3.44Â±2.08/3.57Â±2.21mm/s to 7.12Â±3.84/10.26Â±5.82mm/s). Right kidney had more pronounced motion displacement and faster motion velocity than left kidney, although not yet significant. Motion velocity of left/right kidney in SI was 4.56Â±1.28/4.74Â±1.87mm/s, significantly faster than the velocity of 1.28Â±0.51/1.99Â±1.07 mm/s in AP (p<0.001, t-test). Motion velocity in LR was not reported here due to the small LR motion range and thus the registration uncertainty. Significantly faster velocity was found for both left/right kidneys when they moved superiorly (5.53Â±1.50/6.01Â±2.08 mm/s, during exhalation) than moved inferiorly (4.15Â±1.03/4.90Â±1.71 mm/s, during inhalation) (p<0.001, t-test).
Conclusion: In addition to the conventionally used respiratory phase and motion amplitude, motion velocity information could be potentially used for planning and gating of MR-guided stereotactic ablative body radiotherapy (SABR) of renal cell carcinoma to improve motion management.