PurposeA study of real-time adaptive radiotherapy systems was performed to test the hypothesis that, across delivery systems and institutions, the dosimetric accuracy is improved with adaptive treatments over non-adaptive radiotherapy in the presence of patient-measured tumor motion.Methods and materialsTen institutions with robotic(2), gimbaled(2), MLC(4) or couch tracking(2) used common materials including CT and structure sets, motion traces and planning protocols to create a lung and a prostate plan. For each motion trace, the plan was delivered twice to a moving dosimeter; with and without real-time adaptation. Each measurement was compared to a static measurement and the percentage of failed points for γ-tests recorded.ResultsFor all lung traces all measurement sets show improved dose accuracy with a mean 2%/2 mm γ-fail rate of 1.6% with adaptation and 15.2% without adaptation (p < 0.001). For all prostate the mean 2%/2 mm γ-fail rate was 1.4% with adaptation and 17.3% without adaptation (p < 0.001). The difference between the four systems was small with an average 2%/2 mm γ-fail rate of <3% for all systems with adaptation for lung and prostate.ConclusionsThe investigated systems all accounted for realistic tumor motion accurately and performed to a similar high standard, with real-time adaptation significantly outperforming non-adaptive delivery methods.
Couch and MLC tracking markedly improved the geometric and dosimetric accuracies of VMAT delivery. However, the two tracking types have different strengths and weaknesses. While couch tracking can correct perfectly for slowly moving targets such as the prostate, MLC tracking may have considerably larger dose errors for persistent target shift perpendicular to the MLC leaves. Advantages of MLC tracking include faster dynamics with better adaptation to fast moving targets, the avoidance of moving the patient, and the potential to track target rotations and deformations.
Context. Shocks produced by outflows from young stars are often observed as bow-shaped structures in which the H 2 line strength and morphology are characteristic of the physical and chemical environments and the velocity of the impact. Aims. We present a 3D model of interstellar bow shocks propagating in a homogeneous molecular medium with a uniform magnetic field. The model enables us to estimate the shock conditions in observed flows. As an example, we show how the model can reproduce rovibrational H 2 observations of a bow shock in OMC1.Methods. The 3D model is constructed by associating a planar shock with every point on a 3D bow skeleton. The planar shocks are modelled with a highly sophisticated chemical reaction network that is essential for predicting accurate shock widths and line emissions. The shock conditions vary along the bow surface and determine the shock type, the local thickness, and brightness of the bow shell. The motion of the cooling gas parallel to the bow surface is also considered. The bow shock can move at an arbitrary inclination to the magnetic field and to the observer, and we model the projected morphology and radial velocity distribution in the plane-of-sky. Results. The morphology of a bow shock is highly dependent on the orientation of the magnetic field and the inclination of the flow. Bow shocks can appear in many different guises and do not necessarily show a characteristic bow shape. The ratio of the H 2 v = 2−1 S(1) line to the v = 1−0 S(1) line is variable across the flow and the spatial offset between the peaks of the lines may be used to estimate the inclination of the flow. The radial velocity comes to a maximum behind the apparent apex of the bow shock when the flow is seen at an inclination different from face-on. Under certain circumstances the radial velocity of an expanding bow shock can show the same signatures as a rotating flow. In this case a velocity gradient perpendicular to the outflow direction is a projection effect of an expanding bow shock lighting up asymmetrically because of the orientation of the magnetic field. With the 3D model we reproduce the brightness levels in three H 2 lines as well as the shape and size of a chosen bow shock in OMC1. The inferred bow inclination and the orientation and strength of the magnetic field fit into the pattern suggested by independent observations.
Aims. We seek to study excitation mechanisms in the inner region of the Orion Molecular Cloud by comparing observations of orthoand para-lines of H 2 with theoretical models of slow shocks and photodissociation regions. Methods. K-band observations of H 2 obtained with the Canada-France-Hawaii 3.6 m telescope using the PUEO adaptive optics system are reported. Data were centered on the Becklin-Neugebauer object northwest of the Trapezium stars. Narrow-band filters were used to isolate emission from the v = 1-0 S(1) ortho-and v = 1-0 S(0) para-lines at a spatial resolution of 0. 45 (∼200 AU). We are able to combine their intensity to obtain the column densities of rovibrationally excited ortho and para H 2 levels of the molecular gas at high spatial resolution. Results. The resulting line ratios show variations between 2 and the statistical equilibrium value of 6. We find 4 different classes of emission, characterised by the ratio of the v = 1-0 S(1) and S(0) line brightness and the absolute line brightness. Shock models are used to estimate the physical properties of pre-shock density and shock velocity for these 4 classes. We find that the pre-shock density is in the range of 10 5-10 7 cm −3 and shock velocities lie between 10 and 40 km s −1. Studies of individual objects, using additional constraints of shock velocity and width, allow quite precise physical conditions to be specified in three prominent bow shocks, one with a shock speed of 18 ± 2 km s −1 and pre-shock density 1 ± 0.5 × 10 6 cm −3 (3σ) and two with shock speeds of ∼36 ± 2 km s −1 and pre-shock densities of 7.5 ± 2.5 × 10 4 cm −3 .
Aims. We present a new method for reproducing high spatial resolution observations of bow shocks by using 1D plane parallel shock models. As an example we analyse one bow shock located in the Orion Molecular Cloud (OMC1). Methods. We use high spatial resolution near-infrared observations of H 2 rovibrational emission to constrain shock models. These observations have been made at the ESO-VLT using a combination of the NACO adaptive optics system and infrared camera array and the Fabry-Perot interferometer. Three rovibrational H 2 lines have been observed: v = 1−0 S(1) at 2.12 µm, v = 1−0 S(0) at 2.23 µm and v = 2−1 S(1) at 2.25 µm. The spatial resolution is 0. 15 ∼ 70 AU. We analyse a single bow shock located in our field, featuring a very well defined morphology and high brightness. Results. One dimensional shock models are combined to estimate the physical properties of pre-shock density, shock velocity and transverse magnetic field strength along the bow shock. We find that the pre-shock density is constant at ∼5 × 10 5 cm −3 and shock velocities lie between ∼35 km s −1 in the wings of the shock and ∼50 km s −1 at the apex. We also find that the transverse magnetic field is stronger at the apex and weaker further down the wings varying between ∼2 and 4 mGauss. Predictions of shock velocity and magnetic field strength agree with previous independent observations.
Multileaf collimator (MLC) tracking is a promising and clinically emerging treatment modality for radiotherapy of mobile tumours. Still, new quality assurance (QA) methods are warranted to safely introduce MLC tracking in the clinic. The purpose of this study was to create and experimentally validate a simple model for fast motion-including dose error reconstruction applicable to intrafractional QA of MLC tracking treatments of moving targets.MLC tracking experiments were performed on a standard linear accelerator with prototype MLC tracking software guided by an electromagnetic transponder system. A three-axis motion stage reproduced eight representative tumour trajectories; four lung and four prostate. Low and high modulation 6 MV single-arc volumetric modulated arc therapy treatment plans were delivered for each trajectory with and without MLC tracking, as well as without motion for reference. Temporally resolved doses were measured during all treatments using a biplanar dosimeter. Offline, the dose delivered to each of 1069 diodes in the dosimeter was reconstructed with 500 ms temporal resolution by a motion-including pencil beam convolution algorithm developed in-house. The accuracy of the algorithm for reconstruction of dose and motion-induced dose errors throughout the tracking and non-tracking beam deliveries was quantified. Doses were reconstructed with a mean dose difference relative to the measurements of-0.5% (5.5% standard deviation) for cumulative dose. More importantly, the root-mean-square deviation between reconstructed and measured motion-induced 3%/3 mm γ failure rates (dose error) was 2.6%. The mean computation time for each calculation of dose and dose error was 295 ms. The motion-including dose reconstruction allows accurate temporal and spatial pinpointing of errors in absorbed dose and is adequately fast to be feasible for online use. An online implementation could allow treatment intervention in case of erroneous dose delivery in both tracking and non-tracking treatments.
Real-time delivery-specific QA during radiotherapy of moving targets was demonstrated for the first time. It allows supervision of treatment accuracy and action on treatment discrepancy within 2 s with high sensitivity and specificity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.