OC-0186: Real-time long-term multi-object tracking on cineMR using a tracking-learning-detection framework
Jennifer Dhont, Davide Cusumano, Luca Boldrini, Giuditta Chiloiro, L. Azario, Francesco Cellini, M. De Spirito, Luboš Omelina, Jef Vandemeulebroucke, Dirk Verellen, Vincenzo Valentini · Radiotherapy and Oncology · 2018
Purpose or ObjectiveVerification of intra-fractional tumor position during gated delivery is of utmost importance.We integrated gated breath-hold delivery under MRI guidance with only 3 mm margins using video-feedback to patients, and report on the accuracy of the real-time gated delivery system and reproducibility of tumor position. Material and MethodsMR-guided gated breath-hold SBRT delivery in combination with visual feedback was implemented with the MRIdian system (Viewray Inc, Mountain View, USA).During treatment delivery, real-time tumor tracking is realized through repeated fast planar MR imaging in a single sagittal plane at 4 frames-per-second with 3.5mm x 3.5mm in-plane resolution via deformable image registration.An in-room MR-compatible monitor allows projection of this sagittal image with visualization of both the tracked GTV contour and gating boundary, which is the PTV (GTV+3mm).For each delivery, a threshold ROI% is set which determines the maximum allowed percentage of the GTV-area that can be outside the gating window before triggering a beam-hold.Accuracy of the real-time gated delivery and reproducibility of tumor position during repeated breathholds was analyzed for 15 patients with five lung-, adrenal-and pancreas tumors each for a total of 87 fractions, resulting in a cumulative 33.4 hours of MR-cine.For image analysis, bi-cubic interpolation was applied to all acquired frames resulting in images with 0.8mmx0.8mmresolution.For each fraction we analyzed:[1] reproducibility of the GTV-centroid (GTV-COM) position within the PTV; [2] the geometric coverage of the GTV-area within the PTV; [3] treatment duty cycle efficiency; [4] effects of threshold ROI%-settings on treatment duty cycle efficiency and GTV-area coverage.Results Figure 1 shows a single 2D planar tracking image for a lung patient with observed GTV-COM positions, relative to the PTV-COM during beam-on.Grouped results showed 5 th -95 th percentile distributions of GTV-COM positions, relative to PTV-COM, in AP [ventral-dorsal] direction of [-3.3mm,+2.8mm],[-2.5mm,+3.7mm]and [-4.4mm,+2.9mm]for lung-, adrenal-and pancreas tumors, respectively.The corresponding distributions in CC [caudal-cranial] direction were [-2.6mm,+4.6mm],[-4.1mm,+4.4mm]and [-4.4mm,+4.5mm],respectively.However, the mean GTV-areas that were encompassed by the PTV during beam-on across all fractions were 94.6%, 94.3% and 95.3% for lung-, adrenal-and pancreas tumors.The mean treatment duty cycle efficiency ranged from 67% to 87% for tumor sites.Selecting a higher threshold ROI% resulted in increased duty cycle efficiency, at the cost of a slight decrease in GTV area coverage.