A new isocentric technique for exact geometric matching in the radiotherapy of the breast and ipsilateral supraclavicular fossa using dual asymmetric jaws

BackgroundIn some clinical situations breast or chest wall radiotherapy for cancer is given in association with supraclavicular fossa irradiation. Often the treatment is delivered by two tangential fields to the breast or chest wall and an anterior field that irradiates the supraclavicular region. The tissue between the breast or chest wall and the supraclavicular region may be under or overdosed, because of the junction between the two tangential fields and the anterior field.PurposeTo present a new isocentric technique for exact geometric matching between the two tangential fields and the anterior field.MethodsPatients are positioned with both arms raised. Using three-dimensional trigonometry, two half-fields, with isocenter between the breast and the supraclavicular region, are easily matched. The tangential fields have a collimator rotation to protect the lung without additional shielding. The correct gantry, collimator and couch positions are defined for the anterior field to match the tangential fields.ConclusionsA general formula for exact geometric matching in radiotherapy of the breast and supraclavicular fossa is presented. The method does not require additional shielding to eliminate divergence other than the four independent jaws. The result is simple to implement in modern delivery facilities.     

Field matching in breast irradiation

INTRODUCTION: In this paper the authors have combined different irradiation techniques for breast and adjacent supraclavicular lymph nodes. The aim was to reduce inhomogeneity in the match-line. METHODS: The CadPlan 6.1.5 three-dimensional treatment planning system was applied in this study for CT based plan using a standard medial and lateral wedged tangential breast portals with the adjacent supraclavicular field. Isocenter is placed at depth on the match-line, where asymmetric jaws are used to produce non-divergent field edges. The tangential fields are shaped using multi-leaf collimator (MLC), by following the curvature of the thorax. In this way the cranial vertical match plane is maintaned without using the breast board. The prescribed dose was 50 Gy at the isocentre. RESULTS: The calculated dose distributions were evaluated in three dimension in the match region of supraclavicular field and the two opposing tangential fields. This method produces a more uniform dose distribution in the target volume and in the match-line. Set-up is fast, this is done without the need for table rotation, or vertical cephalad blocks. The average dose to the ipsilateral lung is reduced using the IMRT (intensity modulated radiotherapy) technique by approximately 10% compared with the conventional technique. Furthermore, this new technique has the possibility to improve the field match between the tangential fields and the parasternal field, while maintaning the field match between the tangential fields and the axillary and supraclavicular fields.     

Mechanical quality assurance using light field for linear accelerators with camera calibration

Mechanical Quality Assurance (QA) is important to assure spatially precise delivery of external-beam radiation therapy. As an alternative to the conventional-film based method, we have developed a new tool for mechanical QA of LINACs which uses a light field rather than radiation. When light passes through the collimator, a shadow is projected onto a piece of translucent paper and the resulting image is captured by a digital camera via a mirror. With this method, we evaluated the position of the LINAC isocenter and the accuracy of the gantry, collimator, and couch rotation. We also evaluated the accuracy of the digital readouts of the gantry, collimator, and couch rotation. In addition, the treatment couch position indicator was tested. We performed camera calibration as an essential pre-requisite for quantitative measurements of the position of isocenter, the linear motion of the couch, and the rotation angles of the gantry and collimator. Camera calibration reduced the measurement error to submillimeter based on uncertainty in pixel size of the image, while, without calibration, the measurement error of up to 2 mm could occur for an object with a length of 5 cm.     

Automatic verification of SSD and generation of respiratory signal with lasers in radiotherapy: A preliminary study

PurposeSource to surface distance (SSD) plays a very important role in external beam radiotherapy treatment verification. In this study, a simple technique has been developed to verify the SSD automatically with lasers. The study also suggests a methodology for determining the respiratory signal with lasers.MethodsTwo lasers, red and green are mounted on the collimator head of a Clinac 2300 C/D linac along with a camera to determine the SSD. A software (SSDLas) was developed to estimate the SSD automatically from the images captured by a 12-megapixel camera. To determine the SSD to a patient surface, the external body contour of the central axis transverse computed tomography (CT) cut is imported into the software. Another important aspect in radiotherapy is the generation of respiratory signal. The changes in the lasers separation as the patient breathes are converted to produce a respiratory signal. Multiple frames of laser images were acquired from the camera mounted on the collimator head and each frame was analyzed with SSDLas to generate the respiratory signal.ResultsThe SSD as observed with the ODI on the machine and SSD measured by the SSDlas software was found to be within the tolerance limit. The methodology described for generating the respiratory signals will be useful for the treatment of mobile tumors such as lung, liver, breast, pancreas etc.ConclusionThe technique described for determining the SSD and the generation of respiratory signals using lasers is cost effective and simple to implement.     

Evaluation of optimization workflow using design of experiment (DoE) for various field configurations in volumetric-modulated arc therapy

PurposeIn volumetric-modulated arc therapy (VMAT), field configurations such as couch or arc angles are defined manually or using a template. A field configuration is reselected through trial-and-error in the case of undesirable resultant planning. To efficiently plan for desirable quality, configurations should be assessed before dose calculation. Design of experiments (DoE) is an optimization technique that efficiently reveals the influence of inputs on outputs. We developed an original tool using DoE to determine the field configuration selection and evaluated the efficacy of this workflow for clinical practice.MethodsComputed-tomography scans of 17 patients and target structures were acquired retrospectively from a brain tumor treated using a dual-arc VMAT plan. The configurations of the couch, arc, collimator angles, field sizes, and beam energy were determined using DoE. The resultant dose distributions obtained using the DoE-selected configuration were compared with the clinical plan.ResultsThe averaged differences between the DoE and clinical plan for 17 patients of doses to 50% of the planning target volume (PTV-D50%), Brain-D60%, Brain-D30%, Brain stem-D1%, Left eye-D1%, Right eye-D1%, Optic nerve-D1%, and Chiasm-D1% were 0.2 ± 0.5%, −1.0 ± 4.6%, 1.7 ± 3.5%, −2.5 ± 6.7%, −0.2 ± 4.9%, −1.2 ± 3.6%, −2.8 ± 7.3%, and −2.1 ± 5.7%, respectively.ConclusionsOur optimization workflow obtained using DoE for various field configurations provided the same or slightly superior plan quality compared with that created by experts. This process is feasible for clinical practice and will efficiently improve treatment quality while removing the influence of the planner’s experience.     

Dosimetric accuracy of dual isocenter irradiation in low magnetic field resonance guided radiotherapy system for extended abdominal tumours

PurposeDue to limited field size of Magnetic Resonance Linear Accelerators (MR-Linac), some treatments could require a dual-isocenter planning approach to achieve a complete target coverage and thus exploit the benefits of the online adaptation. This study evaluates the dosimetric accuracy of the dual-isocenter intensity modulated radiation therapy (IMRT) delivery technique for MR-Linac.Material and MethodsDual-isocenter multi leaf collimator (MLC) and couch accuracy tests have been performed to evaluate the delivery accuracy of the system. A mono-isocenter plan delivered in clinical practice has then been retrospectively re-planned with dual-isocenter technique. The dual-isocenter plan has been re-calculated and delivered on a 3-dimensional (3D) ArcCHECK phantom and 2-dimensional (2D) films to assess its dosimetric accuracy in terms of gamma analysis. Clinical and planning target volume (CTV and PTV respectively) coverage robustness was then investigated after the introduction of ± 2 mm and ± 5 mm positioning errors by shifting the couch.ResultsMLC and couch accuracy tests confirmed the system accuracy in delivering a dual-isocenter irradiation.2D/3D gamma analysis results occurred always to be above 95% if considered a gamma criteria 1%/2 mm and 1%/1 mm respectively for the 2D and 3D analysis.The mean variations for CTV D98% and PTV V95% were 0.2% and 1.1% respectively when positioning error was introduced separately in each direction, while the maximum observed variations were 0.9% (CTV) and 3.7% (PTV).ConclusionThe dosimetric accuracy of dual-isocenter irradiation has been verified for MR-Linac, achieving accurate and robust treatment strategy and improving dose conformality also in presence of targets whose extension exceeds the nominal maximum field size.     

Numerical analysis of maximal bat performance in baseball

Metal baseball bats have been experimentally demonstrated to produce higher ball exit velocity (BEV) than wooden bats. In the United States, all bats are subject to BEV tests using hitting machines that rotate the bat in a horizontal plane. In this paper, a model of bat-ball impact was developed based on 3-D translational and rotational kinematics of a swing performed by high-level players. The model was designed to simulate the maximal performance of specific models of a wooden bat and a metal bat when swung by a player, and included material properties and kinematics specific to each bat. Impact dynamics were quantified using the finite element method (ANSYS/LSDYNA, version 6.1). Maximum BEV from both a metal (61.5 m/s) and a wooden (50.9 m/s) bat exceeded the 43.1 m/s threshold by which bats are certified as appropriate for commercial sale. The lower BEV from the wooden bat was attributed to a lower pre-impact bat linear velocity, and a more oblique impact that resulted in a greater proportion of BEV being lost to lateral and vertical motion. The results demonstrate the importance of factoring bat linear velocity and spatial orientation into tests of maximal bat performance, and have implications for the design of metal baseball bats.     

Comparison of three different phantoms used for Winston-Lutz test with Artiscan software

BackgroundOne of the most important test in every quality assurances process of medical linear accelerators is the Winston-Lutz test, allowing an evaluation of the treatment isocentre in the light of uncertainty of the position of the collimator, the gantry and the couch.AimThe purpose of this work was analysis of the results of the Winston-Lutz test performed with three different phantoms for two different accelerators.Materials and methodsMeasurements were performed on two Varian machines: TrueBeam equipped with aS1200 EPID and TrueBeam equipped with aS1000 EPID. During the study three different phantoms dedicated for verification of the radiation isocentre were used: PTW Isoball, AQUILAB Isocentre Phantom and Varian Isocentre Cube. Analysis of the DICOM images was performed in Artiscan software.ResultsFor TrueBeam with as1200 EPID, gantry MV isocentre was about 0.18 mm larger for Varian Isocentre Cube than for two other phantoms used in this study. The largest variability of this parameter was observed for the couch. The results differed to 1.16 mm. For TrueBeam with as1000 EPID, results for collimator isocentre with PTW Isoball phantom were about 0.10 mm larger than for two other phantoms. For the gantry, results obtained with Varian Isocentre Cube were 0.21 mm larger.ConclusionThe obtained results for all three phantoms are within the accepted tolerance range. The largest differences were observed for treatment couch, which may be related to the phantom mobility during couch movement.     

Simple fractal method of assessment of histological images for application in medical diagnostics

We propose new method of assessment of histological images for medical diagnostics. 2-D image is preprocessed to form 1-D landscapes or 1-D signature of the image contour and then their complexity is analyzed using Higuchi's fractal dimension method. The method may have broad medical application, from choosing implant materials to differentiation between benign masses and malignant breast tumors.     

Gamma index comparison of three VMAT QA systems and evaluation of their sensitivity to delivery errors

PurposeTo compare detectors for dosimetric verification before VMAT treatments and evaluate their sensitivity to errors.Methods and materialsMeasurements using three detectors (ArcCheck, 2d array 729 and EPID) were used to validate the dosimetric accuracy of the VMAT delivery. Firstly, performance of the three devices was studied. Secondly, to assess the reliability of the detectors, 59 VMAT treatment plans from a variety of clinical sites were considered. Thirdly, systematic variations in collimator, couch and gantry angle plus MLC positioning were applied to four clinical treatments (two prostate, two head and neck cases) in order to establish the detection sensitivity of the three devices. Measurements were compared with TPS computed doses via gamma analysis (3%/3 mm and 2%/2 mm) with an agreement of at least 95% and 90% respectively in all pixels. Effect of the errors on the dose distributions was analyzed.ResultsRepeatability and reproducibility were excellent for the three devices. The average pass rate for the 59 cases was superior to 98% for all devices with 3%/3 mm criteria. It was found that for the plans delivered with errors, the sensitivity was quite similar for all devices. Devices were able to detect a 2 mm opened or closed MLC error with 3%/3 mm tolerance level. An error of 3° in collimator, gantry or couch rotation was detected by the three devices using 2%/2 mm criteria.ConclusionsAll three devices have the potential to detect errors with more or less the same threshold. Nevertheless, there is no guarantee that pretreatment QA will catch delivery errors.     

Binding affinity prediction of novel estrogen receptor ligands using receptor-based 3-D QSAR methods

We have recently reported the development of a 3-D QSAR model for estrogen receptor ligands showing a significant correlation between calculated molecular interaction fields and experimentally measured binding affinity. The ligand alignment obtained from docking simulations was taken as basis for a comparative field analysis applying the GRID/GOLPE program. Using the interaction field derived with a water probe and applying the smart region definition (SRD) variable selection procedure, a significant and robust model was obtained (q²_LOO=0.921, SDEP=0.345). To further analyze the robustness and the predictivity of the established model several recently developed estrogen receptor ligands were selected as external test set. An excellent agreement between predicted and experimental binding data was obtained indicated by an external SDEP of 0.531. Two other traditionally used prediction techniques were applied in order to check the performance of the receptor-based 3-D QSAR procedure. The interaction energies calculated on the basis of receptor–ligand complexes were correlated with experimentally observed affinities. Also ligand-based 3-D QSAR models were generated using program FlexS. The interaction energy-based model, as well as the ligand-based 3-D QSAR models yielded models with lower predictivity. The comparison with the interaction energy-based model and with the ligand-based 3-D QSAR models, respectively, indicates that the combination of receptor-based and 3-D QSAR methods is able to improve the quality of prediction.     

Determining substrate displacement and cell traction fields--a new approach

This paper presents a new approach for the traction force microscopy (TFM) method which determines traction forces exerted by adherent cells on a thin, elastic polyacrylamide gel embedded with fluorescent microbeads. In this enhanced TFM method, a pattern recognition technique is first applied to match the pair of microbead embedded images before and after deformation, which subsequently provides the displacement field of the elastic substrate. Once the displacement field is obtained, the 3-D finite element method (FEM) is used to compute cell traction forces. The new TFM has been applied to determine traction forces of human tendon fibroblasts. Compared to existing TFM methods, the present method has the following advantages: (1) its displacement field obtained is associated with microbead movements; (2) it considers the finite thickness of the thin polyacrylamide gel and is therefore free from the infinite half-space approximation adopted by existing TFM methods; and (3) its computation procedure for determining cell traction forces is fast.     

An application for assessing quality of RNA hybridized to Affymetrix GeneChips

This paper describes a stand-alone application for estimating the 3' to 5' ratio by fitting a mixed effects model to the interior pixel intensities of perfect match probes for selected control probe sets from an Affymetrix *.DAT file. The effectiveness of this method was demonstrated previously by an application of the method to two microarray datasets for which external verification of RNA quality was known. This application provides a more objective assessment of sample quality in that both a point estimate and 95% confidence interval about the 3' to 5' ratio are provided. AVAILABILITY: The software and installation instructions are freely available for download at http://www.people.vcu.edu/~kjarcher/Research/Data.htm     

Mammobarography: a possible method of mass breast screening

Preliminary details are given of a novel method of detecting breast lumps. The technique relies on the fact that such a lump will cause a perturbation in the pressure distribution when the breast is loaded against a flat plate. The pressure distribution is monitored by using the principle of frustrated total internal reflection to generate a brightness distribution which can then be presented as a contour map in synthesized colour. Using this technique, simulated lumps in breast prostheses have been detected down to a diameter of 6 mm. It is argued that this represents the basis of a method of mass breast screening.     

Characterization of Asymmetric Tapered Dipole Nanoantenna for Energy Harvesting Applications

In this paper, systematic study for asymmetric tapered dipole nanoantenna is implemented using finite element frequency domain (FEFD) solver where harvesting efficiency, field confinement, surface current, and input impedance are calculated at wavelength of 500 nm. The proposed nanoantennas achieve a harvesting efficiency of 61.3% and a field enhancement factor of 37.7 over the conventional dipole nanoantenna. This enhancement is attributed to the irregularity of the surface current distribution on the asymmetric designs. Particle swarm optimization technique is used to find the optimum design geometrical parameters through an external link between the optimization algorithm and the FEFD solver. Moreover, the proposed designs offer a resonance impedance of 500 Ω to match that of fabricated rectifiers. Further study of the structure fabrication tolerance is included which shows the robustness of the proposed nanoantennas.     

Noninvasive measurements of transmural myocardial metabolites using 3-D (31)P NMR spectroscopy

A completely noninvasive three-dimensional (3-D) static magnetic field magnitude spatially localized (31)P spectroscopy technique has been developed and applied to study the in vivo canine myocardium at 9.4 T. The technique incorporates both Fourier series windows and selective Fourier transform methods utilizing all three orthogonal gradients for 3-D phase encoding. The number of data acquisitions for each phase-encoding step was weighted according to the Fourier coefficients to define cylindrical voxels. Spatially localized (31)P spectra can be generated for voxels of desired location within the field of view as a postprocessing step. The quality of localization was first demonstrated by using a three-compartment phantom. The technique was then applied to in vivo canine models and yielded (31)P cardiac spectra with an excellent signal-to-noise ratio. The in vivo validation experiments, using an implanted 2-phosphoenolpyruvate-containing marker, demonstrated that the technique is capable of measuring at least two transmural layers of left ventricular myocardium representing the subepicardium and subendocardium.     

Pectoralis major "trapdoor" flap for silicone breast implant medial knuckle deformities.

Loss of breast parenchyma through surgery and physiologic involution can lead to problems of subglandular silicone breast implant palpability and even contour irregularities. This can give rise to patient concern and detracts from the aesthetics of the breast augmentation, particularly when it occurs medially. We present a simple solution to this problem on the medial side of the breast in the form of a small segmental medially based pectoralis major "trapdoor" flap that augments the implant soft-tissue cover intracapsularly, at the site where it is deficient. The technique, which has been used with success in five patients over 3 years, is described.