Rotational Offsets Research Articles

SU‐E‐T‐375: Evaluation of the Ability of Three Commercially Available Dosimeters to Detect Systematic Delivery Errors in IMRT Plans

Purpose: To evaluate the sensitivity of three patient‐specific IMRT QA devices to systematic delivery errors. Methods: Four clinical step‐and‐shoot IMRT plans were selected, two simple prostate, one medium complexity head and neck (H&N) and one complex H&N. Twelve plan variations with errors introduced were created: Multi‐Leaf Collimator (MLC) positional errors (all leaf pairs shifted in the same direction (1, 2, 3 mm) and opposite direction (1, 2, 3 mm)); collimator rotation offsets (1, 2, 3 degrees) and gantry rotation offsets (0.5, 1, 2 degrees). The total dose for each plan was measured using an ArcCHECK helical diode array. Each field for each plan, excluding those with gantry offsets, was measured using an Electronic Portal Imager and a MatriXX Evolution 2D ionisation chamber array. The measured dose was compared to the calculated dose for the no error plan using Gamma analysis with 3%/3mm, 3%/2mm, and 2%/2mm criteria. Results: The ability of the different devices to detect errors was similar. In most cases pass rates reduced with increasing errors and/or stricter gamma criteria as expected. The ArcCHECK demonstrated sensitivity to 2 degree gantry errors, with a reduction in pass rate of 6–14% between the 1 and 2 degree errors in all plans for all gamma criteria. Even for the 2%/2mm criteria, no device detected a 3 degree collimator error in either prostate plan, however collimator errors were detected for the H&N plans which had elongated fields. For all criteria, there were different scenarios for each detector where MLC position errors of 3 mm were not detected. Conclusion: None of the devices could reliably detect MLC position or collimator rotation errors that were not within recommended linear accelerator monthly QA tolerances. There were no consistent differences between the ability of the devices to detect systematic delivery errors. Financial support has been provided by the Saudi Arabian Cultural Mission towards this work.

An accuracy assessment of different rigid body image registration methods and robotic couch positional corrections using a novel phantom

Image guided radiotherapy (IGRT) using cone beam computed tomography (CBCT) images greatly reduces interfractional patient positional uncertainties. An understanding of uncertainties in the IGRT process itself is essential to ensure appropriate use of this technology. The purpose of this study was to develop a phantom capable of assessing the accuracy of IGRT hardware and software including a 6 degrees of freedom patient positioning system and to investigate the accuracy of the Elekta XVI system in combination with the HexaPOD robotic treatment couch top. The constructed phantom enabled verification of the three automatic rigid body registrations (gray value, bone, seed) available in the Elekta XVI software and includes an adjustable mount that introduces known rotational offsets to the phantom from its reference position. Repeated positioning of the phantom was undertaken to assess phantom rotational accuracy. Using this phantom the accuracy of the XVI registration algorithms was assessed considering CBCT hardware factors and image resolution together with the residual error in the overall image guidance process when positional corrections were performed through the HexaPOD couch system. The phantom positioning was found to be within 0.04 (σ = 0.12)°, 0.02 (σ = 0.13)°, and -0.03 (σ = 0.06)° in X, Y, and Z directions, respectively, enabling assessment of IGRT with a 6 degrees of freedom patient positioning system. The gray value registration algorithm showed the least error in calculated offsets with maximum mean difference of -0.2(σ = 0.4) mm in translational and -0.1(σ = 0.1)° in rotational directions for all image resolutions. Bone and seed registration were found to be sensitive to CBCT image resolution. Seed registration was found to be most sensitive demonstrating a maximum mean error of -0.3(σ = 0.9) mm and -1.4(σ = 1.7)° in translational and rotational directions over low resolution images, and this is reduced to -0.1(σ = 0.2) mm and -0.1(σ = 0.79)° using high resolution images. The phantom, capable of rotating independently about three orthogonal axes was successfully used to assess the accuracy of an IGRT system considering 6 degrees of freedom. The overall residual error in the image guidance process of XVI in combination with the HexaPOD couch was demonstrated to be less than 0.3 mm and 0.3° in translational and rotational directions when using the gray value registration with high resolution CBCT images. However, the residual error, especially in rotational directions, may increase when the seed registration is used with low resolution images.

The sensitivity of a lower limb model to axial rotation offsets and muscle bounds at the knee

Soft tissue artifacts during motion capture can lead to errors in kinematics and incorrect estimation of joint angles and segment motion. The aim of this study was to evaluate the effect of shank segment axial rotation and knee rotator muscle bounds on predicted muscle and joint forces in a musculoskeletal model of the lower limb. A maximal height jump for ten subjects was analysed using the original motion data and then modified for different levels of internal and external rotation, and with the upper force bound doubled for five muscles. Both externally rotating the shank and doubling the muscle bounds increased the ability of the model to find a solution in regions of high loading. Muscle force levels in popliteus and tensor fascia latae showed statistically significant differences, but less so in plantaris, sartorius or gracilis. The shear and patellofemoral joint forces were found to be significantly affected by axial rotation during specific phases of the motion and were dependent on the amount of rotation. Fewer differences were observed when doubling the muscle bounds, except for the patellofemoral force and plantaris and sartorius muscle force, which were significantly increased in many of the jump phases. These results give an insight into the behaviour of the model and give an indication of the importance of accurate kinematics and subject-specific geometry.

Insight into the 3D Architecture and Quasicrystal Symmetry of Multilayer Nanorod Assemblies from Moiré Interference Patterns

Vertical nanorod assembly over three dimensions is shown to result in the formation of Moiré interference patterns arising from rotational offsets between respective monolayer sheets. Six distinct patterns are observed in HRTEM and angular dark-field STEM (DF-STEM) images, allowing the exact angle of rotation to be determined from their respective size and repeat order. At large rotation angles approaching 30°, the aperiodicity in the structure of the nanorod supercrystals becomes apparent, resulting in 12-fold ordering characteristics of a quasicrystal. The rotational offsets are further elucidated from Fourier transform and small angle electron diffraction, allowing interpretation of several multilayers when combined with DF-STEM and SEM. Pattern formation owing to angular rotation is differentiated from those occurring from a lateral shift, providing an important insight into the complex multilayered structures in assembled rods that may have an impact on their collective electronic or photonic properties. We also show how random tetrapods when present at low concentrations in colloidal nanorod solutions act as termination points for 2D sheet crystallization, impacting the size and shape of the resultant assemblies. The occurrence of Moiré patterns in rod assemblies demonstrates the extraordinary order achievable in their assembly and offers a nondestructive technique to precisely map the placement of each nanorod in this important nanoarchitecture.

Cultural Heritage Recording Utilising Low-Cost Closerange Photogrammetry

Cultural heritage is under a constant threat of damage or even destruction and comprehensive and accurate recording is necessary to attenuate the risk of losing heritage or serve as basis for reconstruction. Cost effective and easy to use methods are required to record cultural heritage, particularly during a world recession, and close-range photogrammetry has proven potential in this area. Off-the-shelf digital cameras can be used to rapidly acquire data at low cost, allowing non-experts to become involved. Exterior orientation of the camera during exposure ideally needs to be established for every image, traditionally requiring known coordinated target points. Establishing these points is time consuming and costly and using targets can be often undesirable on sensitive sites. MEMS-based sensors can assist in overcoming this problem by providing small-size and low-cost means to directly determine exterior orientation for close-range photogrammetry. This paper describes development of an image-based recording system, comprising an off-the-shelf digital SLR camera, a MEMS-based 3D orientation sensor and a GPS antenna. All system components were assembled in a compact and rigid frame that allows calibration of rotational and positional offsets between the components. The project involves collaboration between English Heritage and Loughborough University and the intention is to assess the system’s achievable accuracy and practicability in a heritage recording environment. Tests were conducted at Loughborough University and a case study at St. Catherine’s Oratory on the Isle of Wight, UK. These demonstrate that the data recorded by the system can indeed meet the accuracy requirements for heritage recording at medium accuracy (1-4cm), with either a single or even no control points. As the recording system has been configured with a focus on low-cost and easy-to-use components, it is believed to be suitable for heritage recording by non-specialists. This offers the opportunity for lay people to become more involved in their local heritage, an important aspiration identified by English Heritage. Recently, mobile phones (smartphones) with integrated camera and MEMS-based orientation and positioning sensors have become available. When orientation and position during camera exposure is extracted, these phones establish off-the-shelf systems that can facilitate image-based recording with direct exterior orientation determination. Due to their small size and low-cost they have potential to further enhance the involvement of lay-people in heritage recording. The accuracy currently achievable will be presented also.

Fiducial registration error as a statistical process control metric in image-guidance radiotherapy with fiducial markers

Portal imaging of implanted fiducial markers has been in use for image-guided radiotherapy (IGRT) of prostate cancer, with ample attention to localization accuracy and organ motion. The geometric uncertainties in point-based rigid-body matching algorithms during localization of prostate fiducial markers can be quantified in terms of a fiducial registration error (FRE). In this study, the aim is to demonstrate how statistical process control (SPC) can be used to intercept potential problems with rigid-body matching algorithms in a retrospective study of FRE for a pilot cohort of 34 patients with fiducial markers. A procedure for estimating control parameters of a SPC control chart (x-chart) from a small number of initial observations (N) of FRE was implemented. The sensitivity analysis of N on the number of ‘in-control’ and ‘out-of-control’ x-charts was also performed. Uncorrected rotational offsets of an individual patient were examined to elucidate possible correlations with the behaviours of an x-chart. Four specific types of qualitative x-chart behaviour have been observed. The number of out-of-control processes was insensitive to the choice of N, provided N ⩾ 5. Residual errors of rigid-body registration were contributed from uncorrected rotational offsets in 5 out of 15 ‘out-of-control’ x-charts. Out-of-control x-charts were also shown to be correlated with potential changes in the IGRT processes, which may compromise the quality of the radiation treatment delivery. The SPC methodology, implemented in the form of individually customized x-charts, has been shown to be a useful tool for monitoring process reliability during fiducial-based IGRT for prostate cancer.

Dosimetric consequences of rotational errors in radiation therapy of pediatric brain tumor patients

PurposeTo quantify the rotational offsets and estimate the dose effect of rotation on the target volume and normal tissues in children with brain tumor. MethodsTwenty-one pediatric patients with brain tumors were included in this study. Cone-beam CT was performed before each treatment and at the end of every other treatment. Translational offsets were corrected before the treatment. An offline analysis was performed to quantify rotational errors. The treatment plans were altered and recalculated to simulate a rotation of 2° and 4°, and the dose changes were quantified. Results1016 CBCT datasets were analyzed for this report. The mean of the rotations were not meaningfully different from zero. 18.1% of the fractions had rotations with a magnitude ⩾2°, 5.0% had rotations ⩾3° and 0.9% had rotations ⩾4°. For the 2° rotational simulation, the gEUD values of the PTV and critical structures changed by less than 2%. For the 4° simulation, parallel type normal structures had minor changes (<2%), but serial type normal structures and the PTV had changes of 10% and 5%, respectively. ConclusionsThe majority of rotational errors observed were less than 1°. A rotational error of 2° produced negligible changes in the gEUD to critical structures or target volumes. Rotational errors ⩾4° produced undesirable results, therefore, at a minimum, errors >2° should be corrected.

Feasibility study of performing IGRT system daily QA using a commercial QA device

The purpose of this study was to investigate the feasibility of using a single QA device for comprehensive, efficient daily QA of a linear accelerator (Linac) and three image‐guided stereotactic positioning systems (IGSPSs). The Sun Nuclear Daily QA 3 (DQA3) device was used to perform daily dosimetry and mechanical accuracy tests for an Elekta Linac, as well as daily image geometric and isocenter coincidence accuracy tests for three IGSPSs: the AlignRT surface imaging system; the frameless SonArray optical tracking System (FSA) and the Elekta kV CBCT. The DQA3 can also be used for couch positioning, repositioning, and rotational tests during the monthly QA. Based on phantom imaging, the Linac coordinate system determined using AlignRT was within 0.7 mm/0.6° of that of the CBCT system. The difference is attributable to the different calibration methods that are utilized for these two systems. The laser alignment was within 0.5 mm of the isocenter location determined with the three IGSPSs. The ODI constancy was ± 0.5 mm. For gantry and table angles of 0°, the mean isocenter displacement vectors determined using the three systems were within 0.7 mm and 0.6° of one another. Isocenter rotational offsets measured with the systems were all ≤ 0.5°. For photon and electron beams tested over a period of eight months, the output was verified to remain within 2%, energy variations were within 2%, and the symmetry and flatness were within 1%. The field size and light‐radiation coincidence were within 1mm ± 1 mm. For dosimetry reproducibility, the standard deviation was within 0.2% for all tests and all energies, except for photon energy variation which was 0.6%. The total measurement time for all tasks took less than 15 minutes per QA session compared to 40 minutes with our previous procedure, which utilized an individual QA device for each IGSPS. The DQA3 can be used for accurate and efficient Linac and IGSPS daily QA. It shortens QA device setup time, eliminates errors introduced by changing phantoms to perform different tests, and streamlines the task of performing dosimetric checks.PACS number: 87.56.Fc

The influence of cam geometry and operating conditions on chaotic mixing of viscous fluids in a twin cam mixer

AbstractSmooth particle hydrodynamica (SPH) simulations were used to better understand the mixing performance of a class of two‐dimensional Twin Cam mixers. The chaotic manifolds of the flow are used to describe the mixing and to identify isolated regions. For an equilateral triangle cam geometry, a figure‐eight manifold structure traps a layer of fluid against the cam boundaries. Changes in the differential rotation and phase offsets between the cams results in modest improvements in the mixing rate across the manifold barrier. Reducing the apex angle of the triangle changes the manifold structure and allows the trapped layer of fluid to mix more effectively with the rest of the domain. This article shows that examining the chaotic manifolds within a typical industrial mixer can provide valuable insight into both the transient and long‐term mixing processes, leading to a more focused exploration of possible mixer configurations and to practical improvements in mixing efficiency. © 2010 American Institute of Chemical Engineers AIChE J, 2011

Polarization dependence of an edge filter based on singlemode–multimode–singlemode fibre

The polarization dependent loss (PDL) of a singlemode–multimode–singlemode (SMS) fibre structure used as an edge filter is presented. Minor errors in the fabrication process for the SMS fibre structure can introduce SMS fibre core offsets. The PDL due to lateral and rotational core offsets is investigated numerically and experimentally. It is shown that small core offsets are necessary to achieve low PDL for an SMS fibre based edge filter. It is also demonstrated that when lateral core offsets are unavoidable, the PDL of a SMS edge filter can still be minimized by introducing a rotational core offset of 90 °.

CT Guidance is Needed to Achieve Reproducible Positioning of the Mouse Head for Repeat Precision Cranial Irradiation

To study the effects of cranial irradiation, we have constructed an all-plastic mouse bed equipped with an immobilizing head holder. The bed integrates with our in-house Small Animal Radiation Research Platform (SARRP) for precision focal irradiation experiments and cone-beam CT. We assessed the reproducibility of our head holder to determine the need for CT-based targeting in cranial irradiation studies. To measure the holder's reproducibility, a C57BL/6 mouse was positioned and CT-scanned nine times. Image sets were loaded into the Pinnacle(3) radiation treatment planning system and were registered to one another by one investigator using rigid body alignment of the cranial regions. Rotational and translational offsets were measured. The average vector shift between scans was 0.80 +/- 0.49 mm. Such a shift is too large to selectively treat subregions of the mouse brain. In response, we use onboard imaging to guide cranial irradiation applications that require sub-millimeter precision.

Region of Interest Tracking in Real-Time Myocardial Contrast Echocardiography

The real-time myocardial contrast echocardiography (RT MCE) is a new echocardiography technology, which allows clinicians to noninvasively evaluate the perfusion of myocardial capillary of patients, using the quantitative analysis of RT MCE. But the accurate analysis requires tracking the position of region of interest (ROI) within the myocardial area, so as to compensate for the translation or rotation offsets, which are due to such uncontrollable factors as heart motion. We used diamond search method and Brox's coarse-to-fine warping optical flow technique for this ROI tracking problem. We validated our methods by comparing the quantitative analysis results of RT MCE using our methods with those using Lucas & Kanade's optical flow technique, which had been report to be accurate enough for this ROI tracking. We finally present some examples of animal experiment to show the effectiveness and the clinical application value of our ROI tracking methods.

TH-D-351-07: Evaluation of Automatic Volume Match Function for Kilovoltage Cone-Beam CT (CBCT) Guided Patient Setup

Purpose: To evaluate the automatic volume match function provided by a commercial Cone‐beam CT(CBCT) guided patient setup system. Method and Materials:CBCTimages from 10 patients treated with stereotactic body radiotherapy for primary livercancers in the stereotactic frame were acquired by On‐board Imager (OBI, Varian Medical System) following initial treatment setup. Manual volume registration of CBCT to the planning CT was performed by physicians to adjust patient positioning. Retrospective automatic volume match was also performed for each dataset and compared to the manual registration. To further assess the automatic volume match, simulation of patient rotational offsets was generated. Automatic volume matching of the simulated data was used to investigate potential setup errors due to patient roll. Results: A total of 27 CBCT datasets were acquired and analyzed. The average differences between manual and automatic match are 2.4±1.7mm, 3.2±2.6mm and 1.8±1.6mm in the right‐left, superior‐inferior and anterior‐posterior directions, respectively. The simulation study demonstrated a significant limitation of the automatic 4 degrees of freedom (4DOF) correction mode with regard to the patient's rotational offset. This occurs because the 6 degrees of freedom (6DOF) registration algorithm is always internally applied, even in 4DOF shift calculation mode, although the two dimensions of pitch/roll offsets are not displayed. Our simulation revealed that this can cause patient setup error which becomes significant as the distance between the patient rotation axis and the treatment isocenter increases. Conclusion: Caution needs to be taken when using automatic volume match function for CBCT‐guided patient setup since the conventional treatment couch is only capable of translational and limited rotational shifts. Using the full degrees of freedom automatic volume match without caution can lead to significant error in patient treatment.

Evaluation of abduction range of motion and avoidance of inferior scapular impingement in a reverse shoulder model

The purpose of this study was to determine the effects of prosthetic design and surgical technique of reverse shoulder implants on total abduction range of motion and impingement on the inferior scapular neck. Custom implants in three glenosphere diameters (30, 36, and 42 mm), with 3 different centers of rotation offsets (0, +5, and +10 mm), were placed into a Sawbones scapula (Pacific Research Laboratories, Vashon, WA) in 3 different positions: superior, center, and inferior glenoid. Humeral sockets were manufactured with a 130 degrees , 150 degrees , and 170 degrees neck-shaft angle. Four independent factors (glenosphere diameter, center of rotation offset, glenosphere position on the glenoid, and humeral neck-shaft angle) were compared with the 2 dependent factors of range of motion and inferior scapular impingement. Center of rotation offset had the largest effect on range of motion, followed by glenosphere position. Neck-shaft angle had the largest effect on inferior scapular impingement, followed by glenosphere position. This information may be useful to the surgeon when deciding on the appropriate reverse implant.

Comment on “Image‐guided patient positioning: if one cannot correct for rotational offsets in external‐beam radiotherapy setup, how should rotational offsets be managed?” [Med. Phys., – (2007)

Comment on “Image‐guided patient positioning: if one cannot correct for rotational offsets in external‐beam radiotherapy setup, how should rotational offsets be managed?” [Med. Phys., – (2007)

Image‐guided patient positioning: If one cannot correct for rotational offsets in external‐beam radiotherapy setup, how should rotational offsets be managed?

When setting up patients via image-guided positioning for external-beam radiotherapy, one can often determine the rotational corrections needed for optimal alignment, but once measured, they are not always applied. However, in rigid-body setup calculations the optimal translational component of the setup correction will be different depending on whether rotations are included or excluded from the correction procedure. Furthermore, if rotations go uncorrected then the optimal translation becomes dependent on the relative locations of the registration landmarks, the treatment site, and the rotational axes. If one is not going to make rotational adjustments to the patient position, then two guidelines should be followed: (1) the registration landmarks should closely demarcate the treatment site, and (2) rotational degrees of freedom should not be included in the calculation of setup adjustments.

Effect of Core Twisting on Self‐Assembly and Optical Properties of Perylene Bisimide Dyes in Solution and Columnar Liquid Crystalline Phases

A series of highly soluble and fluorescent core-twisted perylene bisimide dyes (PBIs) 3 a-f with different substituents at the bay area (1,6,7,12 positions of the perylene core) were synthesized and fully characterized by (1)H NMR, UV/Vis spectroscopy, MS spectrometry, and elemental analysis. The pi-pi aggregation properties of these new functional dyes were investigated in detail both in solution and in condensed phase by UV/Vis and fluorescence spectroscopy, vapor pressure osmometry (VPO), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction. Concentration-dependent UV/Vis measurements and VPO analysis revealed that these core-twisted pi-conjugated systems show distinct self-dimerization equilibria in apolar solvent methylcyclohexane (MCH) with dimerization constants between 1.3x10(4) and 30 M(-1). The photoluminescence spectra of the dimers of PBIs 3 a-f exhibit bathochromic shifts of quite different magnitude which could be attributed to different longitudinal or rotational offsets between the dyes as well as differences in the respective pi-pi stacking distance. In condensed state, quite a few of these PBIs form luminescent rectangular or hexagonal columnar liquid crystalline phases with low isotropization temperatures. The effects of the distortion of the pi systems on their pi-pi stacking and the optical properties of the resultant stacks in solution and in LC phases have been explored in detail. In one case (3 a) a particularly interesting phase change from crystalline into liquid crystalline could be observed upon annealing that was accompanied by a transformation from non-fluorescent H-type into strongly fluorescent J-type packing of the dyes.

Precession from Hipparcos and FK5 proper motions compared with current values: Reasons for discrepancies

The comparison of Hipparcos and FK5 proper motions points to an inconsistency with the correction, , of the luni-solar precession derived from VLBI and LLR observations with unprecedented accuracy. An attempt is made to explain this inconsistency of approximately -1.3 mas/yr by rotational offsets of the Hipparcos and FK5 proper motion systems. In terms of right ascension and declination, these offsets give rise to proper motion offsets in the range of ±1 mas/yr on average which is not exceptional given the FK5 error budget. In the case of Hipparcos it is proven that the proper motions are not affected by rotational offsets larger than those indicated by the errors of the proper motion link to the ICRF. This result is obtained by analysing the Hipparcos proper motions in view of the existence of additional systematic motions other than those caused by galactic rotation and the parallactic motion of stars due to the solar motion with respect to the LSR. It is concluded that the Hipparcos proper motions are nearly free of unmodelled rotations, confirming that the Hipparcos frame is inertial at the accuracy level of the proper motion link to the ICRF. The gap between the estimated precessional corrections is bridged primarily by minor changes in the FK5 proper motions of the order of their errors, and only to a small extent by the elimination of a bias in the Hipparcos proper motions.

Connectors for self-reconfiguring robots

Connectors for self-reconfiguring robots are difficult to design because of the wide range of requirements. We describe the DRAGON connector, whose most distinctive features are its ability to self-align and its strength-to-weight ratio. It weighs 170 g, but holds over 70-kg load. It is able to self-align /spl plusmn/15 mm (O/5) lateral offsets and /spl plusmn/45/spl deg/ directional and rotational offsets. It allows autonomous docking and reconfiguration in a fraction of a second, without any complex control.

Robust midsagittal plane extraction from normal and pathological 3-D neuroradiology images.

This paper focuses on extracting the ideal midsagittal plane (iMSP) from three-dimensional (3-D) normal and pathological neuroimages. The main challenges in this work are the structural asymmetry that may exist in pathological brains, and the anisotropic, unevenly sampled image data that is common in clinical practice. We present an edge-based, cross-correlation approach that decomposes the plane fitting problem into discovery of two-dimensional symmetry axes on each slice, followed by a robust estimation of plane parameters. The algorithm's tolerance to brain asymmetries, input image offsets and image noise is quantitatively evaluated. We find that the algorithm can extract the iMSP from input 3-D images with 1) large asymmetrical lesions; 2) arbitrary initial rotation offsets; 3) low signal-to-noise ratio or high bias field. The iMSP algorithm is compared with an approach based on maximization of mutual information registration, and is found to exhibit superior performance under adverse conditions. Finally, no statistically significant difference is found between the midsagittal plane computed by the iMSP algorithm and that estimated by two trained neuroradiologists.