Single 4D Research Articles

WE-E-J-6C-05: Variability of Four Dimensional CT Patient Models

Purpose: Several studies address the use of 4D CT to increase the geometrical accuracy of radiotherapy for lung cancer patients. A single 4D CT scan, however, gives a ‘snapshot’ movie loop of the patient's respiratory motion. In this study, we investigated the variability of respiratory motion over the course of radiotherapy using repeated 4D cone beam CT (4DCBCT) scans. Method and Materials: 4DCBCT scans of 10 lung cancer patients were acquired on the linac just prior to irradiation for 7–13 fractions. The diaphragm motion, extracted automatically from the projection images, was analyzed in terms of period and phase-histogram (relative time spend in [exhale, exhale-to-inhale, inhale and inhale-to-exhale]). Tumor motion was determined by registering a region of interest from the planning CT to each phase of the 4DCBCT. Results: The average breathing period ranged from 2.1 s to 5.6 s for different patients, with an inter- and intra-fraction variation of 0.8 s SD. The average phase histogram was [0.3 0.23 0.2 0.27] with little variation between fractions and patients, i.e., patients generally spend more time at exhale than inhale. The mean (over all patients) intra-fraction variation (SD) of the average tumor position relative to the bony anatomy was 1.6 mm LR, 2.7 mm SI and 2.3 mm AP, reflecting baseline breathing variation. The peak-to-peak tumor motion ranged from 0.4 to 2.0 cm, with an inter-fraction variability of 16% (1SD). Conclusion: Substantial variation in respiratory frequency, mean tumor position and peak-to-peak amplitude was found. These uncertainties can be taken into account by adapting the CTV-to-PTV margin accordingly. 4D-patient models should be regularly updated, e.g., by acquiring 4DCBCT prior to treatment, for safe implementation of precision 4D radiotherapy techniques like gating and tracking. Conflict of Interest: This research was sponsored by Elekta Oncology Systems Ltd.

4D Monte Carlo simulation of proton beam scanning: modelling of variations in time and space to study the interplay between scanning pattern and time-dependent patient geometry

When dosimetric effects in time-dependent geometries are studied, usually either the results of individual three-dimensional (3D) calculations are combined or probability-based approaches are applied. These methods may become cumbersome and time-consuming if high time resolution is required or if the geometry is complex. Furthermore, it is difficult to study double-dynamic systems, e.g., to investigate the influence of time-dependent beam delivery (i.e., magnetically moving beam spots in proton beam scanning) on the dose deposition in a moving target. We recently introduced the technique of 4D Monte Carlo dose calculation to model continuously changing geometries. In intensity modulated proton therapy, dose is delivered by individual pristine Bragg curves. Dose spots are positioned in the patient by varying magnetic field and beam energy. If the movement of these dose spots occurs during significant respiratory motion, interplay effects can take place. Because of the inhomogeneity of individual subfields, the consequences of motion can be more severe than in conventional proton therapy. We demonstrate how the technique of 4D Monte Carlo can be used to study interplay effects in proton beam scanning. Time-dependent beam delivery to a changing patient geometry is simulated in a single 4D dose calculation. Interplay effects between respiratory motion and beam scanning speed are demonstrated.

Four-dimensional CT scans for treatment planning in stereotactic radiotherapy for stage I lung cancer

Hypofractionated stereotactic radiotherapy (SRT) for Stage I non-small-cell lung cancer requires that meticulous attention be paid toward ensuring optimal target definition. Two computed tomography (CT) scan techniques for defining internal target volumes (ITV) were evaluated. Ten consecutive patients treated with SRT underwent six "standard" rapid multislice CT scans to generate an ITV(6 CT) and one four-dimensional CT (4DCT) scan that generated volumetric datasets for 10 phases of the respiratory cycle, all of which were used to generate an ITV(4DCT). Geometric and dosimetric analyses were performed for (1) PTV(4DCT), derived from the ITV(4DCT) with the addition of a 3-mm margin; (2) PTV(6 CT), derived from the ITV(6 CT) with the addition of a 3-mm margin; and (3) 6 PTV(10 mm), derived from each separate GTV(6 CT), to which a three-dimensional margin of 10 mm was added. The ITV(4DCT) was not significantly different from the ITV(6 CT) in 8 patients, but was considerably larger in 2 patients whose tumors exhibited the greatest mobility. On average, the ITV(6 CT) missed on average 22% of the volume encompassing both ITVs, in contrast to a corresponding mean value of only 8.3% for ITV(4DCT). Plans based on PTV(4DCT) resulted in coverage of the PTV(6 CT) by the 80% isodose in all patients. However, plans based on use of PTV(6 CT) led to a mean PTV(4DCT) coverage of only 92.5%, with a minimum of 77.7% and 77.5% for the two most mobile tumors. PTVs derived from a single multislice CT expanded with a margin of 10 mm were on average twice the size of PTVs derived using the other methods, but still led to an underdosing in the two most mobile tumors. Individualized ITVs can improve target definition for SRT of Stage I non-small-cell lung cancer, and use of only a single CT scan with a 10-mm margin is inappropriate. A single 4D scan generates comparable or larger ITVs than are generated using six unmonitored rapid CT scans, a finding related to the ability to account for all respiration-correlated mobility.

105 poster workshop Target volume definition for stage I NSCLC: single 4D CT scan vs. one standard vs. six standard CT scans

105 poster workshop Target volume definition for stage I NSCLC: single 4D CT scan vs. one standard vs. six standard CT scans

Defining target volumes for stage I NSCLC using a single 4D CT scan (versus a single standard CT and 6 standard CT scans)

Defining target volumes for stage I NSCLC using a single 4D CT scan (versus a single standard CT and 6 standard CT scans)

Systematics of coupling flows in AdS backgrounds

We give an effective field theory derivation, based on the running of Planck brane gauge correlators, of the large logarithms that arise in the predictions for low energy gauge couplings in compactified ${\mathrm{AdS}}_{5}$ backgrounds, including the one-loop effects of bulk scalars, fermions, and gauge bosons. In contrast with the case of charged scalars coupled to Abelian gauge fields that has been considered previously in the literature, the one-loop corrections are not dominated by a single 4D Kaluza-Klein mode. Nevertheless, in the case of gauge field loops, the amplitudes can be reorganized into a leading logarithmic contribution that is identical to the running in 4D non-Abelian gauge theory, and a term which is not logarithmically enhanced and is analogous to a two-loop effect in 4D. In a warped grand unified theory (GUT) model broken by the Higgs mechanism in the bulk, we show that the matching scale that appears in the large logarithms induced by the non-Abelian gauge fields is ${m}_{\mathrm{XY}}^{2}/k$ where ${m}_{\mathrm{XY}}$ is the bulk mass of the XY bosons and k is the AdS curvature. This is in contrast with the UV scale in the logarithmic contributions of scalars, which is simply the bulk mass m. Our results are summarized in a set of simple rules that can be applied to compute the leading logarithmic predictions for coupling constant relations within a given warped GUT model. We present results for both boundary breaking of the GUT gauge group and bulk breaking through the Higgs mechanism.

Metastable gravitons and infinite volume extra dimensions

We address the issue of whether extra dimensions could have an infinite volume and yet reproduce the effects of observable four-dimensional gravity on a brane. There is no normalizable zero-mode graviton in this case, nevertheless correct Newton's law can be obtained by exchanging bulk gravitons. This can be interpreted as an exchange of a single metastable 4D graviton. Such theories have remarkable phenomenological signatures since the evolution of the Universe becomes high-dimensional at very large scales. Furthermore, the bulk supersymmetry in the infinite volume limit might be preserved while being completely broken on a brane. This gives rise to a possibility of controlling the value of the bulk cosmological constant. Unfortunately, these theories have difficulties in reproducing certain predictions of Einstein's theory related to relativistic sources. This is due to the van Dam–Veltman–Zakharov discontinuity in the propagator of a massive graviton. This suggests that all theories in which contributions to effective 4D gravity come predominantly from the bulk graviton exchange should encounter serious phenomenological difficulties.

Molecular mapping of an aluminum tolerance locus on chromosome 4D of Chinese Spring wheat

The tolerance of aluminum (Al) of disomic substitution lines having the chromosomes of the D genome of Triticum aestivum L. cv. Chinese Spring individually substituted for their homoeologues in T. turgidum L. cv. Langdon was investigated by the hematoxylin method. The disomic substitution lines involving chromosome 4D were more Al tolerant than Langdon. The tolerance was found to be controlled by a single dominant gene, designated Alt2, that is in the proximal region of the long arm of chromosome 4D. The locus was mapped relative to molecular markers utilizing a population of recombinant chromosomes from homoeologous recombination between Chinese Spring chromosome 4D and T. turgidum chromosome 4B. Comparison of the location of Alt2 in this map with a consensus map of chromosomes 4B and 4D based on homologous recombination indicated that Alt2 is in a vicinity of a 4 cM interval delineated by markers Xpsr914 and Xpsr1051. The Alt2 locus is distal to marker Xpsr39 and proximal to XksuC2. The Altw locus is also proximal to the Knal locus on chromosome 4D that controls K+/Na+ selectivity and salt tolerance. In two lines, Alt 2 and Knal were transferred on a single 4D segment into the long arm of T. turgidum chromosome 4B.

Line-Shape Analysis in EPR Spectra of Nb(IV) Complexes in Solutions and Glasses

The EPR spectra of a Nb (IV) complex in alcoholic liquid and solid solution are investigated between 293° and 77°K. The spectra exhibit hyperfine structure originating from interaction of one single 4d electron with the central Nb(I=92) nucleus. At 77°K the spectra show a complicated appearance. In order to analyze the observed spectra a formula for the line shape is derived by assuming a Lorentzian shape function, axial symmetry of both the g and a tensor, and completely randomized orientation of the complexes. With the correct transition probabilities and a certain approximation for the resonance field a closed expression for the line shape of a single hyperfine structure line is given, which readily lends itself to numerical calculation. By use of a computer program the components of the g and a tensor are determined for three different alcohols, methanol, ethanol, and isopropanol, as solvents (see Table IV). It is shown that satisfactory agreement between observed and calculated spectra can only be obtained if anisotropy of the Lorentzian line-shape parameter is assumed besides the well-known dependence of this parameter on the magnetic quantum number m.