Evaluation of radixact motion synchrony for 3D respiratory motion: Modeling accuracy and dosimetric fidelity

Abstract

The Radixact® linear accelerator contains the motion Synchrony system, which tracks and compensates for intrafraction patient motion. For respiratory motion, the system models the motion of the target and synchronizes the delivery of radiation with this motion using the jaws and multi‐leaf collimators (MLCs). It was the purpose of this work to determine the ability of the Synchrony system to track and compensate for different phantom motions using a delivery quality assurance (DQA) workflow. Thirteen helical plans were created on static datasets from liver, lung, and pancreas subjects. Dose distributions were measured using a Delta4® Phantom+ mounted on a Hexamotion® stage for the following three case scenarios for each plan: (a) no phantom motion and no Synchrony (M0S0), (b) phantom motion and no Synchrony (M1S0), and (c) phantom motion with Synchrony (M1S1). The LEDs were placed on the Phantom+ for the 13 patient cases and were placed on a separate one‐dimensional surrogate stage for additional studies to investigate the effect of separate target and surrogate motion. The root‐mean‐square (RMS) error between the Synchrony‐modeled positions and the programmed phantom positions was <1.5 mm for all Synchrony deliveries with the LEDs on the Phantom+. The tracking errors increased slightly when the LEDs were placed on the surrogate stage but were similar to tracking errors observed for other motion tracking systems such as CyberKnife Synchrony. One‐dimensional profiles indicate the effects of motion interplay and dose blurring present in several of the M1S0 plans that are not present in the M1S1 plans. All 13 of the M1S1 measured doses had gamma pass rates (3%/2 mm/10%T) compared to the planned dose > 90%. Only two of the M1S0 measured doses had gamma pass rates > 90%. Motion Synchrony offers a potential alternative to the current, ITV‐based motion management strategy for helical tomotherapy deliveries.

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

“…Intrafraction motion remains a key challenge in radiation therapy. With a steep learning curve, we have The motion tracking accuracy and dose delivery accuracy were demonstrated adequately, 10,14 ; however, it is still desirable to reconstruct the delivered dose based on actual information (eg, delivered sinogram, real-time motion incorporated images). The current dose reconstruction with PreciseART is based on planned sinogram on pretreatment MVCT, not accounting for actual delivered information such as intrafraction motion, variation in motion tracking, and so forth.…”

“…Technical details of the Synchrony on Radixact system have been reported elsewhere. 10,13,14 A brief description of the system is provided. The hardware of the system consists of a kV x-ray source and a detector panel mounted with a 90 offset from the MV beam and a camera mounted on the ceiling to capture motion of a set of light-emitting diodes (LEDs) placed on the patient's skin and treatment couch.…”

Technical Note: Patient dose from kilovoltage radiographs during motion‐synchronized treatments on Radixact®

“…Cumulative dose from kV images throughout many Synchrony fractions can be estimated by scaling the per fraction values provided in this work by the total number of images acquired throughout treatment. In an initial study with 13 Synchrony treatment plans with various fractionation schemes, the number of images per fraction ranged from 50 to 206, and the total number of images over all fractions ranged from 310 to 1920, with an average of 810 images 9 . When scaled to 2000 total images, the largest dose to any structure in Table III would be 1.4 Gy (D 1% to the pubic bone for the endothelium patient).…”

“…In an initial study with 13 Synchrony treatment plans with various fractionation schemes, the number of images per fraction ranged from 50 to 206, and the total number of images over all fractions ranged from 310 to 1920, with an average of 810 images. 9 When scaled to 2000 total images, the largest dose to any structure in Table III would be 1.4 Gy (D 1% to the pubic bone for the endothelium patient). This value is slightly less than 5% of a typical therapeutic dose of 30, or 1.5 Gy.…”

Respiratory Motion Mitigation and Repeatability of Two Diffusion-Weighted MRI Methods Applied to a Murine Model of Spontaneous Pancreatic Cancer

“…However, 4D CT and 4D MRI studies have shown that the amplitude of pancreas movement during breathing is comparable to that of the liver and lungs [ 15 , 16 , 17 ]. For example, Ferris et al demonstrated 5–7-mm root-mean-square displacement of the human pancreas [ 18 ]. To minimize the respiratory motion artifacts, clinical DWI employs rapid acquisition protocols, such as single-shot echo-planar imaging (EPI) following diffusion weighting preparation [ 19 ].…”