Sci—Fri PM: Delivery — 09: Real‐Time MR Tumour Tracking Using a Linac‐MR System

Objective To investigate the feasibility of direct (i.e. no surrogates), real‐time MR tumor tracking using a linac‐MR system.Methods This study is primarily focused on lungtumour tracking due to its extreme range of motion. Lungtumour motions were simulated using two in‐house built MR compatible motion phantoms. Algorithms have been developed to auto‐contour and to track tumor motion in real‐time from 4D MR images. A real‐time MLC controlling system was developed for tumor tracking. Processing time delays between the completion of MR imaging and the beginning of beam delivery in our tracking system have also been investigated. Results and Discussion Both phantoms showed successful MR compatibility, and they were scanned with 3T MRI while in motion. The auto‐contouring algorithm showed promising tumor contouring capabilities. The algorithm was applied to (1) In‐vivo MR images of lungtumor; (2) MR images of healthy lung (coronal, sagittal, transverse) with 10 different tumor shapes inserted; and (3) MR images of motion phantoms. By combining the auto‐contouring algorithm with an MLC controlling system, real‐time MR tumor tracking was demonstrated in principle. Processing time delays of 50∼400 ms were determined for our tracking system.Conclusions A potential real‐time MR tumor tracking using a linac‐MR system was studied. We have demonstrated the feasibility of (1) real‐time tumor auto‐contouring; (2) real‐time beam conformity to the Beam's Eye view shape of the tumor using 4D MR imaging. Processing time delays were investigated.