Precise Verification Research Articles

Clinical Implementation of Adaptive Helical Tomotherapy: A Unique Approach to Image-Guided Intensity Modulated Radiotherapy

Image-guided IMRT is a revolutionary concept whose clinical implementation is rapidly evolving. Methods of executing beam intensity modulation have included individually designed compensators, static multi-leaf collimators (MLC), dynamic MLC, and sequential (serial) tomotherapy. We have developed helical tomotherapy as an innovative solution to overcome some of the limitations of other IMRT systems. The unique physical design of helical tomotherapy allows the realization of the concepts of adaptive radiotherapy and conformal avoidance. In principle, these advances should improve normal tissue sparing and permit dose reconstruction and verification, thereby allowing significant biologically effective dose escalation. Recent radiobiological findings can be translated into altered fractionation schemes that aim to improve the local control and long-term survival. This strategy is being tested at the University of Wisconsin using helical tomotherapy with its highly precise delivery and verification system along with meticulous and practical forms of immobilization. Innovative techniques such optical guidance, respiratory gating, and ultrasound assessments are being designed and tailored for helical tomotherapy use. The intrinsic capability of helical tomotherapy for megavoltage CT (MVCT) imaging for IMRT image-guidance is being optimized. The unique features of helical tomotherapy might allow implementation of image-guided IMRT that was previously impossible or impractical. Here we review the technological, physical, and radiobiological rationale for the ongoing and upcoming clinical trials that will use image-guided IMRT in the form of helical tomotherapy; and we describe our plans for testing our hypotheses in a rigorous prospective fashion.

An NMR relaxometry and gravimetric study of gelatin-free aqueous polyacrylamide dosimeters

In conformal radiation therapy, a high dose of radiation is given to a target volume to increase the probability of cure, and care is taken to minimize the dose to surrounding healthy tissue. The techniques used to achieve this are very complicated and the precise verification of the resulting three-dimensional (3D) dose distribution is required. Polyacrylamide gelatin (PAG) dosimeters with magnetic resonance imaging and optical computed tomography scanning provide the required 3D dosimetry with high spatial resolution. Many basic studies have characterized these chemical dosimeters that polymerize under irradiation. However, the investigation of the fundamental properties of the radiation-induced polymerization in PAG dosimeters is complicated by the presence of the background gelatin matrix. In this work, a gelatin-free model system for the study of the basic radiation-induced polymerization in PAG dosimeters has been developed. Experiments were performed on gelatin-free dosimeters, named aqueous polyacrylamide (APA) dosimeters, containing equal amounts of acrylamide and N,N′-methylene-bisacrylamide. The APA dosimeters were prepared with four different total monomer concentrations (2, 4, 6 and 8% by weight). Nuclear magnetic resonance (NMR) spin–spin and spin–lattice proton relaxation measurements at 20 MHz, and gravimetric analyses performed on all four dosimeters, show a continuous degree of polymerization over the dose range of 0–25 Gy. The developed NMR model explains the relationship observed between the relaxation data and the amount of crosslinked polymer formed at each dose. This model can be extended with gelatin relaxation data to provide a fundamental understanding of radiation-induced polymerization in the conventional PAG dosimeters.

SU-FF-T-209: Electron Arc Therapy with An Elekta SL-25 10 MeV Beam Using a Dedicated Short Applicator

Purpose: To implement the electron arc therapy with an Elekta SL‐25 10 Mev beam using a dedicated short applicator. Method and Materials:. All measurements were done on an Elekta SL‐25 with a 10 MeV electron beam. Radial PDD were characterized for 4 different cylindrical acrylic phantoms using TLDs and Kodak X‐Omat‐V radiographic films The phantom radius (di ) ranged between 5.1 and 15.2 cm, the total arc angles (α) varied between 60° and 160° and the number of monitor units (MU) per degree between 0.5 and 7. The field with at isocenter (w) was varied between 3.7 and 9.8 cm. Based on this data bank, an analytical model was developed for monitor unit (MU) calculation. This model estimates arc beam output at the depth of maximum dose (dmax) as a function of di and α for a given w. A verification of the model precision was done with a new cylindrical phantom. Results:Curve fitting of the complete set of beam output data with w fixed at 7.3 cm was done with an asymptotic relationship between the dose rate at d max and the inverse square of di . The dependence of the beam output on α was introduced by assuming an explicit function of α for each parameter of the model. Results show that the calculated beam output data is a good approximation for all measured data for all phantoms and arc angles: 89% of the calculated values are within ± 3% of the measured ones and all points are within a ± 5% error range. Conclusion: From our results, clinical implementation of the electron arc therapy technique is possible and should be facilitated by the use of our predictive model in the treatment planning process.

CUTTING EDGE ERROR IN PRINCIPAL AXIS MATHOD FOR FIVE-AXIS MACHINING OF SCULPTURED SURFACES

The principal axis method is an advanced cutter positioning technique used for finish machining. But there are some simplifications in this method as it is used for a torus cutter. A detailed analysis about the errors caused by the simplications is presented. A precious equation of the actual cutting edge of torus is set up. The concept of the cutting edge error is brought out and its expression is also deduced, then some key factors are studied in detail. It points out that the cutting edge error is relative to the stepover of cutting path. It will limit the width of cutting strip, and a precision verification should be done when the princle axis method is used in finish machining.

Simulations of pulsating one-dimensional detonations with true fifth order accuracy

A novel, highly accurate numerical scheme based on shock-fitting coupled with fifth order spatial and temporal discretizations is applied to a classical unsteady detonation problem to generate solutions with unprecedented accuracy. The one-dimensional reactive Euler equations for a calorically perfect mixture of ideal gases whose reaction is described by single-step irreversible Arrhenius kinetics are solved in a series of calculations in which the activation energy is varied. In contrast with nearly all known simulations of this problem, which converge at a rate no greater than first order as the spatial and temporal grid is refined, the present method is shown to converge at a rate consistent with the fifth order accuracy of the spatial and temporal discretization schemes. This high accuracy enables more precise verification of known results and prediction of heretofore unknown phenomena. To five significant figures, the scheme faithfully recovers the stability boundary, growth rates, and wave-numbers predicted by an independent linear stability theory in the stable and weakly unstable regime. As the activation energy is increased, a series of period-doubling events are predicted, and the system undergoes a transition to chaos. Consistent with general theories of non-linear dynamics, the bifurcation points are seen to converge at a rate for which the Feigenbaum constant is 4.66 ± 0.09, in close agreement with the true value of 4.669201…. As activation energy is increased further, domains are identified in which the system undergoes a transition from a chaotic state back to one whose limit cycles are characterized by a small number of non-linear oscillatory modes. This result is consistent with behavior of other non-linear dynamical systems, but not typically considered in detonation dynamics. The period and average detonation velocity are calculated for a variety of asymptotically stable limit cycles. The average velocity for such pulsating detonations is found to be slightly greater than the Chapman–Jouguet velocity.

Path slicing

We present a new technique, path slicing , that takes as input a possibly infeasible path to a target location, and eliminates all the operations that are irrelevant towards the reachability of the target location. A path slice is a subsequence of the original path whose infeasibility guarantees the infeasibility of the original path, and whose feasibility guarantees the existence of some feasible variant of the given path that reaches the target location even though the given path may itself be infeasible. Our method combines the ability of program slicing to look at several program paths, with the precision that dynamic slicing enjoys by focusing on a single path. We have implemented Path Slicing to analyze possible counterexamples returned by the software model checker Blast . We show its effectiveness in drastically reducing the size of the counterexamples to less than 1% of their original size. This enables the precise verification of application programs (upto 100KLOC), by allowing the analysis to focus on the part of the counterexample that is relevant to the property being checked.

Design of Slender Composite Bridges Considering Available Support Region Rotation Capacity

The objective of this paper is to present a simple design method which is able to account for slender composite beam ductility when verifying a continuous bridge load carrying capacity. As ductility in the support region of slender composite beams is insufficient for plastic design, a design method is proposed which is able to account for the limited support region ductility and avoids the precise elastic verification of cross sections. In the first part of the paper, the composite beam local behaviour is investigated and the principles for calculating the cross section resistance and available rotation capacity are discussed. In the second part, the various possibilities of using the existing support region ductility are presented together with the corresponding required rotation capacities. Finally, the verifications needed to assure that the beam load carrying capacity is sufficient are presented.

Effect of subthalamic stimulation on mood state in Parkinson’s disease: evaluation of previous facts and problems

In an attempt to clarify the effect of deep brain stimulation (DBS) to the subthalamic nucleus (STN) on mood state, previous evidence and problems were evaluated through a systematic literature search. Twenty three articles reported the effect of STN DBS on mood state in Parkinson's disease (PD), and antidepressant, depressant, and mania-induced effects were reported in 16.7-76%, 2-33.3%, and 4.2-8.1% of the patients treated with STN DBS, respectively. Most articles reported larger subgroups showing antidepressant effects than those showing depressant effects. The average depression scale score of all subjects was improved or unchanged after STN DBS. Although there was a limitation due to the varied results, it was suggested that, in general, STN DBS had an antidepressant effect in PD. However, the studies reporting severe depressant symptoms, such as suicidal attempts, after STN DBS indicated the importance of careful attention to mood state as well as to motor symptoms after STN DBS. It may be crucial to reduce the variation in the results by, for example, the use of standardized protocols and the precise verification of the stimulated region in further investigations to address this issue.

Design and applications of A 3D precision probe

A 3D probe used for NC-copying process is proposed in the paper. The construction of parallel springs is adopted in the probe. It has compact structure and little volume. By adjusting spring force and improving sensitivity, the probe can be used in CMM. Errors of the probe are analysed. Preformances of the probe are verified by test of measuring force, verification of precision of single axis and plane precision.

Formal methods for smart cards: an experience report

This paper presents a case study in the formal specification and verification of a smart card application. The application is an electronic purse implementation, developed by the smart card producer Gemplus as a test case for formal methods for smart cards. It has been annotated (by the authors) with specifications using the Java Modeling Language (JML), a language designed to specify the functional behavior of Java classes. The reason for using JML as a specification language is that several tools are available to check (parts of) the specification w.r.t. an implementation. These tools vary in their level of automation and in the level of correctness they ensure. Several of these tools have been used for the Gemplus case study. We discuss how the usage of these different tools is complementary: large parts of the specification can be checked automatically, while more precise verification methods can be used for the more intricate parts of the specification and implementation. We believe that having such a range of tools available for a single specification language is an important step towards the acceptance of formal methods in industry.

Magnetostratigraphy: the key to a global correlation of the classic Germanic Trias-case study Volpriehausen Formation (Middle Buntsandstein), Central Germany

An integrated lithostratigraphic–magnetostratigraphic study was carried out in order to provide a magnetic record for the Volpriehausen Formation of the classic Germanic Trias. In its type area of Central Germany, the ∼150-m thick Volpriehausen Formation consists of nine small-scale fining-upward cycles, ranging from about 10 to 20 m in thickness. They can readily be correlated over large parts of the Central European Basin using a combination of cyclic stratigraphy and gamma ray logging. Based on this robust high-resolution lithostratigraphic framework, a precise positioning and verification of paleomagnetic data has been realized. To this end, the classic outcrop Kleines Bodetal and the continuously cored well Bockenem A100 were collected, yielding a total of 361 paleomagnetic samples. From about 87% of them, a characteristic remanence was obtained in both the magnetite-bearing gray lithologies as well as the hematite-bearing red-brown lithologies. The between-site correlation allows the creation of a well-defined composite magnetostratigraphy of the uppermost Bernburg Formation to lowermost Detfurth Formation, encompassing a total of five magnetic polarity intervals, which can be combined unambiguously with a recently established polarity scale for the uppermost Zechstein and Lower Buntsandstein. Moreover, the resulting composite magnetostratigraphy can be correlated with corresponding records from the Continental, Boreal, and Tethyan realms. Thus, the Buntsandstein magnetostratigraphy is important in that it provides valuable anchors to link the Germanic Trias high-resolution lithostratigraphy to the biostratigraphically calibrated Triassic substages.

Two-dimensional and quasi-three-dimensional dosimetry of hadron and photon beams with the Magic Cube and the Pixel Ionization Chamber

Two detectors for fast two-dimensional (2D) and quasi-three-dimensional (quasi-3D) verification of the dose delivered by radiotherapy beams have been developed at University and Istituto Nazionale di Fisica Nucleare (INFN) of Torino. The Magic Cube is a stack of strip-segmented ionization chambers interleaved with water-equivalent slabs. The parallel plate ionization chambers have a sensitive area of 24 × 24 cm2, and consist of 0.375 cm wide and 24 cm long strips. There are a total of 64 strips per chamber. The Magic Cube has been tested with the clinical proton beam at Loma Linda University Medical Centre (LLUMC), and was shown to be capable of fast and precise quasi-3D dose verification. The Pixel Ionization Chamber (PXC) is a detector with pixel anode segmentation. It is a 32 × 32 matrix of 1024 cylindrical ionization cells arranged in a square 24 × 24 cm2 area. Each cell has 0.4 cm diameter and 0.55 cm height, at a pitch of 0.75 cm separates the centre of adjacent cells. The sensitive volume of each single ionization cell is 0.07 cm3. The detectors are read out using custom designed front-end microelectronics and a personal computer-based data acquisition system. The PXC has been used to verify dynamic intensity-modulated radiotherapy for head-and-neck and breast cancers.

(Non)-migration of radiopaque markers used for on-line localization of the prostate with an electronic portal imaging device

Purpose Radiopaque gold markers can be implanted in the prostate to visualize its position on portal images during radiation therapy. This procedure assumes that the markers do not move within the prostate. In this work we test this assumptiom. Methods and materials Three markers were implanted transrectally in the prostate of patients undergoing external radiation therapy. An orthogonal pair of portal images was acquired periodically throughout the course of radiation therapy with an a-Si electronic portal imaging device (EPID). The marker coordinates were determined, and the distances between the implanted markers were recorded. The distance time trend is used to evaluate the magnitude of marker migration. Results The average standard deviation (SD) of the distances between markers was 1.3 mm (range 0.44 to 3.04 mm). Three of the 11 patients show a SD larger than 2 mm. For these patients, all three distances show a simultaneous reduction with time, compatible with a shrinking of the prostate. All had been treated with neoadjuvant hormone therapy. For 1 of the 3 patients, this reduction in volume was confirmed with a repeat computed tomographic scan. Conclusion None of the 33 markers studied migrated significantly. The implantation of three radiopaque gold markers enables accurate and precise on-line verification of the prostate position during external beam radiation therapy. The use of three markers provides a tool to monitor prostate position and volume changes that can occur over time due to hormone or radiation therapy.

Factors determining acute normal tissue reactions during postoperative radiotherapy in endometrial cancer: analysis of 317 consecutive cases.

Acute radiotherapy reactions are commonly underestimated and under-reported in the literature. Our aim was to evaluate the incidence and risk factors for acute reactions during postoperative radiotherapy in endometrial cancer patients. Performed was detailed retrospective analysis of 317 endometrial cancer patients given postoperative radiotherapy. Two hundred forty seven patients (78%) received both intracavitary (BRT) and external beam irradiation (EBRT), 49 patients (15%) received only BRT and 21 patients (7%) - only EBRT. BRT included radium (Ra) or cesium (Cs). The mean total dose at 0.5 cm for Ra and Cs was 50.5+/-10.3 Gy and 48.4+/-15.0 Gy, respectively, and the mean dose rate - 0.47+/-0.06 Gy/h and 1.42+/-0.41 Gy/h, respectively. Mean EBRT dose in the ICRU reference point was 49.0+/-3.7 Gy given in fractions of 1.54-2.49 Gy (mean 2.0+/-0.17 Gy). Radiotherapy and Oncology Group classification system was employed to score acute reactions. The impact of patient- and treatment-related factors on the risk of acute bowel and urinary bladder reactions was assessed with uni- and multivariate tests. Acute radiotherapy reactions of any grade occurred in 265 patients (84%) including bowel complications in 66% and urinary bladder complications in 36%. There were 21 severe (grade 3 or 4) reactions, all but one seen in the patients treated with combined EBRT and BRT. Higher total dose (P=0.024), higher EBRT dose (P=0.022) and higher age (P=0.026) were correlated with increased acute bowel toxicity in univariate analysis. Multivariate analysis showed that higher EBRT dose (P=0.015) and older age (P=0.016) were independently correlated with the risk of acute bowel events. Higher total dose (P=0.009), BRT dose (P=0.029), BRT dose rate (P=0.004), EBRT fraction size (P=0.007), the use of Cs BRT (P=0.001) and lower parity (P=0.041) were correlated with increased risk of acute bladder toxicity in univariate test. Multivariate analysis demonstrated that the independent risk factors for acute bladder events were BRT dose rate (P=0.002) and low parity (P=0.042) and there was a trend for EBRT dose (P=0.076). In multivariate analysis there was no impact of other clinical factors (FIGO stage, diabetes mellitus, hypertension, prior abdominal surgery) on the risk of acute bowel and/or bladder reactions nor was the impact of surgery-to-radiotherapy interval, overall radiotherapy time and overall treatment time. The risk of acute reactions depends both on treatment-related (BRT dose rate, EBRT dose) and patient-related factors (age, parity). Precise treatment prescription, planning and verification are of paramount concern. Further studies are warranted to evaluate the impact of extrinsic and intrinsic factors associated with acute normal tissue injury.

High-resolution ground verification, cluster analysis and optical model of reef substrate coverage on Landsat TM imagery (Red Sea, Egypt)

A combination of high-resolution ground verification, cluster analysis using Landsat Thematic Mapper (TM) data, and optical modelling, was applied to Red Sea reef substrate. Ground verification, in an area of 3 by 20 pixels (90 by 600 m) with one metre scale resolution, identified the presence of 30 different bottom types that were later reduced to twelve dominant bottom types. A combination of bispectral plots and principal component analysis using spectral bands 1, 2 and 3 confirmed the presence of nine bottom types. The identified clusters were separated and used as a training set to classify substrate. Optical modelling, using literature radiance values and coverage of the original twelve dominant bottom types and a simple model for atmospheric and water column absorption, revealed a difference of up to 60 W m -2 between predicted substrate radiance and the satellite sensor values in the reef top area. Considering the simple atmospheric correction model, the lack of in situ radiance measurements and the uncertainties with respect to possible changes in bottom type distribution since the acquisition of the 14 year old image, the results show the potential use of satellite imagery for reef research in both biological and geological analysis through very precise and semi-quantitative ground verification, including in situ reflectance measurements.

Intensity-Modulated Radiation Therapy for Breast Cancer

Over the past 2 decades, numerous advances and innovations have occurred in all technical aspects of radiation therapy (RT), including three-dimensional (3D) treatment planning, conformal radiation delivery, intensity-modulated radiation therapy (IMRT), patient immobilization, and precise treatment verification. Despite incredible progress on all fronts, standard RT for breast cancer has changed very little and has not fully exploited many of the advances commonly used to treat most other malignancies. Increasing data have also accumulated, indicating that dose non-uniformities within the breast with traditional RT techniques can be greater than in many other anatomic sites. These significant dose inhomogeneities can produce unnecessary acute and chronic toxicities as well as unacceptable long-term cosmetic results. In addition, the lack of accurate verification of target volume coverage (e.g. lumpectomy cavity or chest wall) may result in diminished tumor control.

Postmarketing special investigation and its verification of precision for cefditoren pivoxil

Postmarketing special investigation and its verification of precision for cefditoren pivoxil

Use of an implanted marker and real-time tracking of the marker for the positioning of prostate and bladder cancers

Purpose: A real-time tracking radiotherapy was investigated to assess its usefulness in precise localization and verification of prostate and bladder cancers. Methods and Materials: The real-time tracking radiation therapy (RTRT) system consists of implantation of a 2.0-mm gold marker into a clinical target volume (CTV), three-dimensional radiation treatment planning (3DRTP) system, and the use of two sets of diagnostic x-ray television systems in the linear accelerator room, image processing units, and an image display unit. The position of the patient can be corrected by adjusting the actual marker position to the planned marker position, which has been transferred from the 3DRTP and superimposed on the fluoroscopic image on the display unit of the RTRT system. The position of the markers can be visualized during irradiation and after treatment delivery to verify the accuracy of the localization. Ten patients with prostate cancer and 5 patients with bladder cancer were examined using this system for the treatment setup on 91 occasions. Results: After manual setup using skin markers, the median of absolute value of discrepancies between the actual position of the marker and the planned position of the marker for prostate cancer was 3.4 (0.1–8.9) mm, 4.1 (0.2–18.1) mm, and 2.3 (0.0–10.6) mm for the lateral, anteroposterior, and craniocaudal directions, respectively. The 3D median distance between the actual and planned positions of the marker was 6.9 (1.1–18.2) mm for prostate cancer and 6.9 (1.7–18.6) mm for bladder cancer. After relocation using RTRT, the 3D distance between the actual and planned position of the marker was 0.9 ± 0.9 mm. Median 3D distances between actual positions after treatment delivery and planned positions were 1.6 (0.0–6.3) mm and 2.0 (0.5–8.0) mm during daily radiotherapy for the marker in patients with prostate cancer and bladder cancer, respectively. Conclusion: We believe the new positioning system can reduce uncertainty due to setup error and internal organ motion, although further improvement is needed for the system to account for the rotational and elastic changes of the affected tissues.

Observations on positivism and pseudoscience in qualitative nursing research.

In this paper I will examine the boundaries between positivism, interpretivism and pseudoscience, arguing that some qualitative researchers may risk the credibility of nursing research by utilizing concepts from the margins of science. There are two major threats to the perceived rigour and credibility of qualitative research in its many forms. First is a trend in some work towards a mystical view of both the methods and the content of the qualitative enterprise. This can be detected, I will argue, in the work of Rosemary Parse in particular. The second potentially damaging trend is almost its epistemological opposite, towards excessive reliance on precise procedures, strict definitions and verification exemplified by Juliet Corbin and others. I will suggest that this is nothing to fear, but something to be clear about. This is not social constructionism or interpretivism but a 'qualitative' version of positivism. The paper concludes that students and researchers should be cautious in the uncritical acceptance of theories and 'research' which approach the boundaries of pseudoscience on the one hand, and 'hard' science on the other.

Quality assurance of serial tomotherapy for head and neck patient treatments

Purpose: A commercial serial tomotherapy intensity-modulated radiation therapy (IMRT) treatment planning (Peacock, NOMOS Corp., Sewickley, PA) and delivery system is in clinical use. The dose distributions are highly conformal, with large dose gradients often surrounding critical structures, and require accurate localization and dose delivery. Accelerator and patient-specific quality assurance (QA) procedures have been developed that address the localization, normalization, and delivery of the IMRT dose distributions. Methods and Materials: The dose distribution delivered by serial tomotherapy is highly sensitive to the accuracy of the longitudinal couch motion. There is also an unknown sensitivity of the dose distribution on the dynamic mutlileaf collimator alignment. QA procedures were implemented that assess these geometric parameters. Evaluations of patient positioning accuracy and stability were conducted by exposing portal films before (single exposure) and after (single or double exposure) treatments. The films were acquired with sequential exposures using the largest available fixed multileaf portal (3.36 × 20 cm 2). Comparison was made against digitally reconstructed radiographs generated using independent software and appropriate beam geometries. The delivered dose was verified using homogeneous cubic phantoms. Radiographic film was used to determine the localization accuracy of the delivered isodose distributions, and ionization chambers and thermoluminescent dosimetry (TLD) chips were used to verify absolute dose at selected points. Ionization chamber measurements were confined to the target dose regions and TLD measurements were obtained throughout the irradiated volumes. Because many more TLD measurements were made, a statistical evaluation of the measured-to–calculated dose ratio was possible. Results: The accelerator QA techniques provided adequate monitoring of the geometric patient movement and dynamic multileaf collimator alignment and positional stability. The absolute delivered dose as measured with the ionization chamber varied from 0.94 to 0.98. Based on these measurements, the delivered monitor units for both subsequent QA measurements and patient treatments were adjusted by the ratio of measured to calculated dose. TLD measurements showed agreement, on average, with the ionization chamber measurements. The distribution of TLD measurements in the high-dose regions indicated that measured doses agreed within 4.2% standard deviation of the calculated doses. In the low-dose regions, the measured doses were on average 5% greater than the calculated doses, due to a lack of leakage dose in the dose calculation algorithm. Conclusions The QA system provided adequate determination of the geometric and dosimetric quantities involved in the use of IMRT for the head and neck. Ionization chamber and TLD measurements provided accurate determination of the absolute delivered dose throughout target volumes and critical structures, and radiographic film yielded precise dose distribution localization verification. Portal film acquisition and subsequent portal film analysis using 3.36 × 20 cm 2 portals proved useful in the evaluation of patient immobilization quality. Adequate bony landmarks were imaged when carefully selected portals were used.