Cross-sectional diagram of the proposed treatment system geometry for EGRT. The PET detector arcs are symmetrically opposed, with a span of 2 cm in the longitudinal direction. During treatment, PET detectors, Linac system, and MV x-ray detectors rotate together around the system isocenter on a slip-ring gantry. The patient table moves in the longitudinal direction so that the treatment is delivered helically.
Illustration of EGRT treatment scheme. (a) shows the process of LOR detection and the beamlets of radiation response. (b) and (c) are enlarged views of the corresponding blocks as labeled in (a). (b) shows the EGRT spatial window, one of the LOR response criteria of the basic EGRT treatment scheme. The LOR (solid/dashed line in (b)) that intersects the source trajectory at a point that falls within the EGRT spatial window (arrow arc in (b)) is qualified for radiation response. (b) and (c) together show the collimator leaf (shaded) closest to the line that connects the source and the midpoint of the LOR-PTV intersection [indicated in (c)].
Illustration of EGRT modulation in the case of attenuation correction. The workflow starts with the shaded module. When one LOR is qualified for response, i.e., it passes the three criteria of the basic EGRT algorithm, the leaf will be opened if the attenuation correction algorithm is not enabled. However, if the modulation algorithm is enabled, the open probability will not be 1. Rather, this LOR will first find its corresponding bin in terms of its spatial orientation in the precalculated attenuation map and the response probability of this LOR, p j , is determined as shown. Note that since only LOR's that intersect the PTV may be responded to, the attenuation map is only calculated for the PTV region.
The simulation flow chart (starting from the shaded module). In an EGRT treatment, there are two major processes to simulate: positron emission and dose delivery. For simulation of the positron emission and detection process, the 4D XCAT phantom is input into the GATE package to obtain the LOR data for dose delivery. The LOR data are used as input for the basic EGRT algorithm and optional EGRT modulation algorithms, such as attenuation correction and integrated dose boost. The resultant set of bMLC configurations is used as inputs to the VMC++ dose calculation engine. The components that enable dynamic EGRT delivery are collectively referred to as “EGRT Engine,” as labeled in the figure.
The dose evaluation scheme for a moving phantom. The periodic motion curve is sampled into N phases. The number (i.e., 1, 2, …, N) in this figure indicates the corresponding phase index. EGRT engine refers to our dynamic EGRT delivery algorithm used to determine the qualified LOR responses. The included components of EGRT engine are labeled in the simulation workflow (Fig. 4). While the gantry and couch are constantly moving in one direction, subsets of bMLC configurations are generated continuously until the treatment ends. Note that these subsets of bMLC configurations are phase-labeled, i.e., each subset belongs to a particular phase. To evaluate the dose that has been accumulated in each phase during the whole treatment, the set of bMLC configurations for each phase is obtained as a summation of subsets of bMLC configurations that correspond to that particular phase. To evaluate the dose accumulated for a specific moving structure (e.g., GTV) during the whole treatment, rigid image registration is used.
The 3D lung tumor trajectory (first phase at the origin). The star and circle markers depict each direction of the tumor round trip, respectively. The peak-to-peak tumor motion amplitude is 16.6, 3.5, and 0.02 mm for superior-inferior (SI), anterior-posterior (AP), lateral-medial (LM) directions, respectively.
Dose maps of all 12 simulated phases in both (a) coronal and (b) sagittal views. Dashed lines are overlaid for positional reference. Each image has a display window of [min max] of itself.
Point-of-view dose maps and associated DVHs for the lung case with (a) EGRT (dashed-dotted lines), (b) conventional method (dashed lines), and (c) EGRT with attenuation correction (solid lines). The GTV is contoured using a black solid line. Note that the curves on OAR's are mostly overlapping with each other.
The dose distributions for (a) original EGRT (dashed-dotted lines), (b) conventional method (dotted lines), (c) boosted EGRT (solid lines), and (d) boosted conventional method (dashed lines) with the associated DVH. The GTV is contoured with a solid line in all scenarios. Contoured PTV, bladder, and rectum are shown only in (b) for simplicity. The boost region is equivalent to the GTV in this case (without a setup error). Note that the curves on OAR's are mostly overlapping with each other.
The dose distribution for (a) original EGRT (dashed-dotted lines), (b) conventional method (dotted lines), (c) boosted EGRT (solid lines), and (d) boosted conventional method (dashed lines) with the associated DVH in the presence of simulated setup error. The GTV is contoured with a solid line in all scenarios. Contoured PTV, bladder, rectum, and boost region are shown only in (b) for simplicity.
A summary of major simulation parameters.
Article metrics loading...
Full text loading...