Management of three-dimensional intrafraction motion through real-time DMLC tracking
Schematic illustration of the various types of target motion as seen in the beam’s view and the desired change in MLC configuration to account for each type of motion.
Logical flow of the real-time DMLC tracking algorithm.
Schematic illustration of the key steps in the tracking algorithm.
Schematic illustration of the leaf fitting operation (a) without and (b) with the use of subleaves.
Experimental arrangement for tracking studies using (a) the lab system and (b) a clinical system.
Image frames extracted from tracking movies acquired to determine the geometric accuracy of DMLC tracking. Two different patterns were separately mounted on the motion platforms to calculate tracking accuracy of (a) motion parallel and perpendicular to MLC leaf travel and (b) motion along the beam axis. In each case, the image frames were segmented in order to determine the peripheral bounds and the center of the MLC aperture (indicated by the outer and inner green circles, respectively) and the central point on the underlying geometric pattern (indicated by the magenta cross). The image frames of the geometric pattern used in (b) were also segmented to delineate the boundary of the white circle (indicated by the magenta outline).
Geometric tracking error in the parallel and perpendicular directions as a function of the number of virtual subleaves used in the DMLC tracking algorithm.
Geometric accuracy of DMLC tracking (using five subleaves) for target motion (a) parallel and (b) perpendicular to MLC leaf travel, and (c) along the beam axis. The horizontal shaded band denotes an error of in (a) and (b) and an error of in (c).
Tracking efficiency in directions (a) parallel and (b) perpendicular to leaf motion. Results are shown for a conformal (circular) and clinically derived D-IMRT and S-IMRT deliveries. Note the different axes in (a) and (b). Beam holds were not asserted by the MLC controller during the VMAT delivery, and therefore the efficiency was 100%.
Isodose (dashed) lines for (a) conformal, (b) D-IMRT (c) S-IMRT, and (d) VMAT deliveries without tracking and corresponding curves [(e), (f), (g), and (h)] with tracking for a target moving parallel and perpendicular to the leaf motion direction. For comparison, isodose curves for delivery to a static object are shown in each figure by solid lines.
Dosimetric error in terms of the percentage of ion-chamber dose values failing a index criterion of 3%, with respect to delivery to a static phantom from the results shown in Fig. 10. When in motion, the target was moving parallel and perpendicular to the direction of leaf motion.
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