SET UP ERRORS AND RECOMMENDED SAFETY MARGINS IN THE PELVIC RADIOTHERAPY FIELDS OF CANCER CERVIX PATIENTS: AN INSTITUTIONAL EXPERIENCE

2016 ◽  
Vol 1 (2) ◽  
Author(s):  
Jitendra Nigam ◽  
Piyush Kumar ◽  
Uthya Balan
Keyword(s):  
Safety Margin ◽  
Conformal Radiotherapy ◽  
Systematic Errors ◽  
Random Errors ◽  
Cancer Cervix ◽  
Lateral Field ◽  
Bony Landmarks ◽  
Safety Margins ◽  
Set Up ◽  
The Individual

INTRODUCTION: Uncertainty exists in radiotherapy delivery due to daily patients set up errors resulting in a difference between planned and delivered dose. The conformal radiotherapy requires reduced margins around the clinical target volume (CTV) with respect to traditional radiotherapy technique and hence these positioning errors are accounted in CTV-PTV margin calculations. The primary aim of this study is to evaluate the set up errors and find out the optimum safety margins for the anterior and lateral fields of pelvis in the patients of cancer cervix treated with 3DCRT by four field box technique. The secondary objective was to study the adequacy of safety margin using the dosimetric and volumetric DVH data. METHODS AND MATERIALS: Study was conducted on twenty one patients of cancer cervix. All patients were immobilsed by full body Vaclok cushions. The radiotherapy to whole pelvis was planned by four field (Anterio-posterior, Posterio-anterior and two laterals) box technique with shielding of corners using multieaf collimators in Varian CLINAC 2300C/D. Weekly EPID images were acquired with Varian aS500 for each patient and were compared with the DRR images using the Portal Vision (Version 7.3.10). The displacement of EPID image from the DRR image was measured by defining reproducible bony landmarks in directions- X (Left to right (LR)), Z (Superior to inferior (SI)) in Anterio-posterior field, and Y (Anterior to posterior (AP)) in lateral field. The systematic and random set up errors for individual and population were calculated. Then the adequate safety margins were calculated by Stroom’s formula. RESULTS: A total of 242 images (42 DRR images and 200 portal images) and 363 match points were evaluated. Set up errors were -7.9 to 8.1mm (LR), -7.3 to 7.3mm (AP) and -9.9 to 8.2mm (SI). The individual systematic errors ranged from -6.6 to 4.9mm (LR), -4.9 to 3.5mm (AP) and -6.3 to 6.5mm (SI) while the individual random errors ranged from 0.5 to 8.3mm (LR), 0.7 to 5.2mm (AP) and 1.1 to 4.6mm (SI). The adequate safety margins which ensures at least 95% of prescribed dose to 99% of the CTV calculated by using Stroom’s formula were 7.9mm (LR), 7.0mm (AP) and 9.1mm (SI). The effect of dose was calculated by simulating a plan by shifting the isocenter along the three axes, where each shift corresponds to the displacement. Dose received by 99% of CTV volume for treatment plans with and without shifts was 99.51±0.81 and 98.63±1.46 respectively. CONCLUSION: In this study, the effect of the systematic errors and the random errors on dose distribution shows that the safety margin of 1 cm appears to be adequate for all the patients.

Set-up verification on a belly-board device using electronic portal imaging

2007 ◽  
Vol 6 (2) ◽  
pp. 73-82 ◽  
Author(s):  
Sarah Roels ◽  
Jan Verstraete ◽  
Karin Haustermans
Keyword(s):  
Time Trends ◽  
Safety Margin ◽  
Patient Positioning ◽  
Random Errors ◽  
Related Factors ◽  
Treatment Unit ◽  
Portal Imaging ◽  
Laser Alignment ◽  
Set Up ◽  
Belly Board

AbstractPurpose: Quantification of set-up errors is necessary to assess the accuracy of patient positioning and define set-up margins. In this article, we describe the analysis of two different set-up verification and correction procedures in pelvic irradiation for rectal cancer patients treated on a belly-board device.Methods: First, we conducted a retrospective study in ten patients. Skin marks were used for set-up and the position was verified and corrected at the start of treatment by portal imaging. Second, we analysed the implementation of a more rigorous verification and correction procedure in ten patients. The same set-up procedure was used, but verification was performed during the first three sessions and on a weekly basis thereafter. In both studies, systematic and random errors were linked with possible patient-related, treatment-unit-related and time-related factors.Results: The pooled data showed a significant reduction in systematic and random error in favour of the second verification procedure (p < 0.05). This resulted in a reduction in the size of the safety margin of more than 3 mm in all directions. Time trends were significant in four patients in the first analysis and in three patients in the second analysis. In six patients in the first and seven patients in the second study, a significant correlation was found between the vertical couch movement and the antero-posterior set-up error. Analysis of patient-related factors demonstrated a relationship between the abdominal contour and rotational errors in both studies.Conclusion: The results of these set-up analyses show that patient positioning on a belly-board device by laser alignment to skin marks is accurate and reproducible. However, in some patients we recommend the implementation of a fixed vertical couch position. The systematic error should be identified and corrected during the first fractions of treatment. Thereafter, verification should be performed at regular intervals to correct for possible time trends. Positioning of obese patients was found to be more prone to set-up errors and requires online position verification.

scholarly journals Calibration of Photometry from the Gemini Multi-Object Spectrograph on Gemini North

2009 ◽  
Vol 26 (1) ◽  
pp. 17-30 ◽  
Author(s):  
Inger Jørgensen
Keyword(s):  
Systematic Errors ◽  
Random Errors ◽  
Standard Star ◽  
Primary Mirror ◽  
Color Terms ◽  
User Community ◽  
Color Term ◽  
The Individual ◽  
Zero Points

AbstractAll available observations of photometric standard stars obtained with the Gemini Multi-Object Spectrograph at Gemini North in the period from August 2001 to December 2003 have been used to establish the calibrations for photometry obtained with the instrument. The calibrations presented in this paper are based on significantly more photometric standard star observations than usually used by the individual users. Nightly photometric zero points as well as color terms are determined. The color terms are expected to be valid for all observations taken prior to UT 2004 November 21 at which time the Gemini North primary mirror was coated with silver instead of aluminium. While the nightly zero points are accurate to 0.02 mag or better (random errors), the accuracy of the calibrations is limited by systematic errors from so-called ‘sky concentration’, an effect seen in all focal reducer instruments. We conclude that an accuracy of 0.035 to 0.05 mag can be achieved by using calibrations derived in this paper. The color terms are strongest for very red objects, e.g. for objects with (r′ – z′) = 3.0 the resulting z′ magnitudes will be ≈0.35 mag too bright if the color term is ignored. The calibrations are of importance to the large Gemini user community with data obtained prior to UT 2004 November 21, as well as future users of achive data from this period in time.

scholarly journals Daily patient geometry correction: application of NAL and eNAL protocols

2020 ◽  
Vol 26 (4) ◽  
pp. 181-184
Author(s):  
Andrzej Dąbrowski ◽  
Sylwia Zielińska-Dąbrowska ◽  
Tomasz Kuszewski ◽  
Krzysztof Lis
Keyword(s):  
Systematic Errors ◽  
Random Errors ◽  
Raw Data ◽  
Total Displacement ◽  
Displacement Vectors ◽  
Daily Data ◽  
Online Corrections ◽  
On Line ◽  
Patient Setup ◽  
Set Up

AbstractPurpose: To test the NAL and eNAL correction protocols using daily patient setup displacements.Methods and material: In total, the analysis was performed for 749 and 797 kV CBCT images for gynecological and prostate patients, respectively, each of 30 patients. After the planning procedure, patients were set up on the treatment table in the treatment position every day. The on-line correction protocol was applied. KV CBCT images were acquired by means of x-ray lamp mounted orthogonally on Linac. Patient setup displacement was assigned. NAL and eNAL corrections protocols were simulated using daily data from online corrections for these two groups of patients. The overall systematic error and random error were calculated for each direction.Results: For the prostate group, the random errors for daily Raw data (no correction) in LAT, LONG, and VERT directions were 2.0 mm, 1.6 mm, and 3.2 mm, respectively. For NAL and eNAL protocols, they were in the range of 1.8 mm to 3.2 mm. For the gynecological group, the random errors were: for daily Raw data 2.2 mm, 1.7 mm, and 3.2 mm, respectively. For NAL and eNAL protocols, they were in the range of 2.0 to 3.4 mm.For the prostate group, values of systematic errors 1.8 mm, 1.8 mm, and 3.3 mm, respectively for Raw data. For NAL and eNAL protocols, these values were less than 1.8 mm. For the gynecological group, the systematic errors were 2.6 mm, 2.3 mm, and 2.8 mm, respectively, for Raw data. For NAL ana eNAL protocols less than 1.8 mm.For the gynecological group, for Raw data, 45% of the total displacement vectors exceeded 5 mm, whereas only 25% did after the NAL procedure and 29% after the eNAL procedure. For the prostate group, for Raw data, 34% of the total displacement vectors exceeded 5 mm, whereas only 22% did after NAL procedure and 28% after eNAL procedure Conclusions: For gynecological and prostate cancer patients, the NAL and eNAL correction protocols can be safely applied to substantially reduce setup errors.

scholarly journals A prospective randomised controlled clinical trial to evaluate three immobilisation devices for intra-thoracic radiation therapy

2010 ◽  
Vol 9 (2) ◽  
pp. 65-75 ◽  
Author(s):  
Evelyn O'Shea ◽  
John Armstrong ◽  
Charles Gillham ◽  
Roisin McCloy ◽  
Rachel Murrells ◽  
...  
Keyword(s):  
Clinical Trial ◽  
Systematic Errors ◽  
Patient Comfort ◽  
Controlled Clinical Trial ◽  
Random Errors ◽  
Thoracic Radiation ◽  
Randomised Controlled Clinical Trial ◽  
Set Up ◽  
Randomised Controlled ◽  
Lung Radiotherapy

AbstractPurpose: To determine the optimal of three immobilisation devices for lung radiotherapy in terms of set-up reproducibility, patient comfort, radiation therapists’ (RTs) satisfaction and cost-effectiveness.Materials and methods: A total of 30 lung CRT patients were randomised to one of three immobilisation techniques – Arm A, headsponge; Arm B, BreastBoard dedicated immobilisation device; and Arm C, LungBoard dedicated immobilisation device.Results: Random errors were larger for Arm A versus C in all directions (p < 0.05). Random errors were larger for Arm A versus B for y and z directions (p < 0.05). When the data for the immobilisation devices (Arms B+C) were pooled and compared with Arm A (no dedicated device), the systematic errors were larger in the z direction for A (p < 0.05). Arm C was cheaper and was more comfortable for patients. Therapists preferred this device (Arm C) and treatment times were less (p < 0.05).Conclusion: This is the first prospective randomised controlled lung immobilisation trial, based on 3-DCRT, that takes into account treatment accuracy, users satisfaction and resource implications. It suggests that the LungBoard immobilisation device is optimal.

scholarly journals A Robust Extended Kalman Filter Applied to Ultrawideband Positioning

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Chuanyang Wang ◽  
Houzeng Han ◽  
Jian Wang ◽  
Hang Yu ◽  
Deng Yang
Keyword(s):  
Kalman Filter ◽  
Extended Kalman Filter ◽  
Robust Estimation ◽  
Hypothesis Test ◽  
Systematic Errors ◽  
Random Errors ◽  
Model Errors ◽  
Global Test ◽  
Practical Applications ◽  
The Individual

Ultrawideband (UWB) is well-suited for indoor positioning due to its high resolution and good penetration through objects. The observation model of UWB positioning is nonlinear. As one of nonlinear filter algorithms, extended Kalman filter (EKF) is widely used to estimate the position. In practical applications, the dynamic estimation is subject to the outliers caused by gross errors. However, the EKF cannot resist the effect of gross errors. The innovation will become abnormally large and the performance and the reliability of the filter algorithm are inevitably influenced. In this study, a robust EKF (REKF) method accompanied by hypothesis test and robust estimation is proposed. To judge the validity of model, the global test based on Mahalanobis distance is implemented to assess whether the test statistical term exceeds the threshold for outlier detection. To reduce and eliminate the effects of the individual outlier, the robust estimation using scheme III of the Institute of Geodesy and Geophysics of China (IGGIII) based on local test of the normalized residual is performed. Meanwhile, three kinds of stochastic models for outliers are expressed by modeling the contaminated distributions. Furthermore, the simulation and measurement experiments are performed to verify the effectiveness and feasibility of the proposed REKF for resisting the outliers. Simulation experiment results are given to demonstrate that the outliers following all the three kinds of contaminated distributions can be detected. The proposed REKF can effectively control the influences of the outliers being treated as systematic errors and large variance random errors. When the outliers come from the thick-tailed distribution, the robust estimation does not play a role, and the REKF are equivalent to the EKF method. The measured experiment results show that the outliers will be generated in the nonline-of-sight environment whose impact is abnormally serious. The robust estimation can provide relatively reliable optimized residuals and control the influences of the outliers caused by gross errors. We can believe that the proposed REKF is effective to resist the effects of outliers and improves the positioning accuracy compared with least-squares (LS) and EKF method. Moreover, the adaptive filter and ranging error model should be considered to compensate the state model errors and ranging systematic errors respectively. Then, the measurement outliers will be detected more correctly, and the robust estimation will be used effectively.

scholarly journals Assessment of set-up errors in the radiotherapy of patients with head and neck cancer: standard vs. individual head support

2020 ◽  
Vol 54 (3) ◽  
pp. 364-370
Author(s):  
Sabina Androjna ◽  
Valerija Zager Marcius ◽  
Primoz Peterlin ◽  
Primoz Strojan
Keyword(s):  
Head And Neck Cancer ◽  
Head And Neck ◽  
Neck Cancer ◽  
Imaging System ◽  
Safety Margin ◽  
Vertical Direction ◽  
Longitudinal Direction ◽  
Treatment Unit ◽  
Safety Margins ◽  
Set Up

AbstractBackgroundThe aim of the study was to (a) compare the accuracy of two different immobilization strategies for patients with head and neck tumors, and (b) compare the set-up errors on treatment units with different portal imaging systems.Patients and methodsVariations in the position of the isocenter (IC) relative to the reference point determined on the computed tomography simulator were measured in a vertical (anterior-posterior), longitudinal (superior-inferior), and lateral (medial-lateral) direction in 120 head and neck cancer patients irradiated with curative intent. Depending on the treatment unit (unit A - 2D/2D image previews; unit B- 2D image previews) and the time of irradiation, patients were divided into 6 groups of 20 patients. In patients irradiated in 2014, standard head supports were used (groups 1 and 2), whereas in those treated in 2015 and 2017 (groups 3–6) individual head supports were employed. The clinical-to-planning target volume safety margin was calculated according to the formula proposed by Van Herk.ResultsIn total, 2,454 portal images and 3,681 set-up errors were analysed. Implementation of individual head supports in 2015 resulted in a statistically significant reduction in the average inter-fraction displacement in the vertical direction and in decreased number of IC displacements in the vertical and longitudinal direction (applies to both treatment units). The largest reduction of the safety margin was calculated in the longitudinal direction and the safety margins were larger for unit B than for unit A.ConclusionsThe use of individual head supports and a more advanced imaging system were found to increase set-up precision.

Statistics and parallaxes

1978 ◽  
Vol 48 ◽  
pp. 7-29
Author(s):  
T. E. Lutz
Keyword(s):  
Experimental Design ◽  
Statistical Methods ◽  
Review Paper ◽  
Systematic Errors ◽  
Past Experience ◽  
Random Errors ◽  
Trigonometric Parallaxes ◽  
Systematic And Random Errors

This review paper deals with the use of statistical methods to evaluate systematic and random errors associated with trigonometric parallaxes. First, systematic errors which arise when using trigonometric parallaxes to calibrate luminosity systems are discussed. Next, determination of the external errors of parallax measurement are reviewed. Observatory corrections are discussed. Schilt’s point, that as the causes of these systematic differences between observatories are not known the computed corrections can not be applied appropriately, is emphasized. However, modern parallax work is sufficiently accurate that it is necessary to determine observatory corrections if full use is to be made of the potential precision of the data. To this end, it is suggested that a prior experimental design is required. Past experience has shown that accidental overlap of observing programs will not suffice to determine observatory corrections which are meaningful.

Patient Scheduling — (Bibliography)

1977 ◽  
Vol 16 (02) ◽  
pp. 112-115 ◽  
Author(s):  
C. O. Köhler ◽  
G. Wagner ◽  
U. Wolber
Keyword(s):  
Information Processing ◽  
Medical Care ◽  
Medical Informatics ◽  
Relevant Literature ◽  
Patient Scheduling ◽  
Individual Scientist ◽  
Set Up ◽  
The Individual ◽  
New Literature ◽  
Current Systems

The entire field of information processing in medicine is today already spread out and branched to such an extent that it is no longer possible to set up a survey on relevant literature as a whole. But even in narrow parts of medical informatics it is hardly possible for the individual scientist to keep up to date with new literature. Strictly defined special bibliographies on certain topics are most helpful.In our days, problems of optimal patient scheduling and exploitation of resources are gaining more and more importance. Scientists are working on the solution of these problems in many places.The bibliography on »Patient Scheduling« presented here contains but a few basic theoretical papers on the problem of waiting queues which are of importance in the area of medical care. Most of the papers cited are concerned with practical approaches to a solution and describe current systems in medicine.In listing the literature, we were assisted by Mrs. Wieland, Mr. Dusberger and Mr. Henn, in data acquisition and computer handling by Mrs. Gieß and Mr. Schlaefer. We wish to thank all those mentioned for their assistance.

STUDY OF INACCURACY IN THE OPERATION OF THE MAIN CONTROLLER OF STB MACHINE

2019 ◽  
Keyword(s):  
Normal Distribution ◽  
Stable Process ◽  
Random Errors ◽  
Actual Length ◽  
Experimental Data Processing ◽  
Set Up ◽  
Main Regulator ◽  
Transmission Gear ◽  
Selection Of

At production of fabrics, including fabrics for agricultural purpose, an important role is played by the cor-rect adjustment of operation of machine main regulator. The quality of setup of machine main controller is determined by the proper selection of rotation angle of warp beam weaving per one filling thread. In the pro-cess of using the regulator as a result of mistakes in adjustment, wear of transmission gear and backlashes in connections of details there are random changes in threads length. The purpose of the article is the research of property of random errors of basis giving by STB machine regulator. Mistakes can be both negative, and positive. In case of emergence only negative or only positive mistakes operation of the machine becomes im-possible as there will be a consecutive accumulation of mistakes. As a result of experimental data processing for stable process of weaving and the invariable diameter of basis threads winding of threads it is revealed that the random error of giving is set up as linear function of the accidental length having normal distribution. Measurements of accidental deviations in giving of a basis by the main regulator allowed to construct a curve of normal distribution of its actual length for one pass of weft thread. The presented curve of distribution of random errors in giving of a basis is the displaced curve of normal distribution of the accidental sizes. Also we define the density of probability of normal distribution of basis giving errors connected with a margin er-ror operation of the main regulator knowing of which allows to plan ways of their decrease that is important for improvement of quality of the produced fabrics.

scholarly journals Nudge Versus Boost: Agency Dynamics Under Libertarian Paternalism

2019 ◽  
Vol 130 (629) ◽  
pp. 1384-1415 ◽  
Author(s):  
Ralph Hertwig ◽  
Michael D Ryall
Keyword(s):  
Cognitive Biases ◽  
Policy Implications ◽  
Best Interests ◽  
Libertarian Paternalism ◽  
The Future ◽  
Set Up ◽  
The Individual

ABSTRACT Thaler and Sunstein (2008) advance the concept of ‘nudge’ policies—non-regulatory and non-fiscal mechanisms designed to enlist people's cognitive biases or motivational deficits so as to guide their behaviour in a desired direction. A core assumption of this approach is that policymakers make artful use of people's cognitive biases and motivational deficits in ways that serve the ultimate interests of the nudged individual. We analyse a model of dynamic policymaking in which the policymaker's preferences are not always aligned with those of the individual. One novelty of our set-up is that the policymaker has the option to implement a ‘boost’ policy, equipping the individual with the competence to overcome the nudge-enabling bias once and for all. Our main result identifies conditions under which the policymaker chooses not to boost in order to preserve the option of using the nudge (and its associated bias) in the future—even though boosting is in the immediate best interests of both the policymaker and the individual. We extend our analysis to situations in which the policymaker can be removed (e.g., through an election) and in which the policymaker is similarly prone to bias. We conclude with a discussion of some policy implications of these findings.

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