Clinical Implementation and Initial Experience of Real-Time Motion Tracking With Jaws and Multileaf Collimator During Helical Tomotherapy Delivery.

ABSTRACT

PURPOSE: This work reports the clinical implementation of a real-time motion tracking and correction system using dynamic multileaf collimator and jaws during helical tomotherapy delivery (Synchrony on Radixact; Accuray, Inc). METHODS AND MATERIALS The first clinical Synchrony on Radixact system was recently installed and tested at our institution. Various clinical workflows, including fiducial implantation, computed tomography simulation, treatment planning, delivery quality assurance, treatment simulation, and delivery, for both fiducial-free and fiducial-based motion tracking methods were developed. Treatment planning and delivery data from initial patients, including dosimetric benefits, real-time target detection, model building, motion tracking accuracy, delivery smoothness, and extra dose from real-time radiographic imaging, were analyzed. RESULTS: The Synchrony on Radixact system was tested to be within its performance specifications and has been used to treat 10 lung (fiducial-free) and 5 prostate (fiducial-based) patients with cancer so far in our clinic. The success of these treatments, especially for fiducial-free tracking, depends on multiple factors, including careful selection of the patient, appropriate setting of system parameters, appropriate positioning of the patient and skin markers, and use of treatment simulation. For the lung tumor cases, difficulties in model building, due primarily to the changes of target detectability or respiration patterns, were observed, which led to important system upgrades, including the addition of a treatment delivery simulation capability. Motion tracking metrics for all treated patients were within specifications, for example, (1) delivery quality assurance passing rates >95%; (2) extra dose from radiograph <0.5% of the prescription dose; and (3) average Potential Diff, measured Δ, and Rigid Body were within 6.5, 2.9, and 3.9 mm, respectively. CONCLUSIONS: Practical workflows for the use of the first clinical motion tracking and correction system in helical tomotherapy delivery have been developed, and the system has now been successfully implemented in our clinic for treating patients with lung and prostate cancer.