Intentional Errors Research Articles

Sensitivity and specificity of time resolved point dose measurements for patient specific quality assurance

This study aimed to quantify the sensitivity and specificity of time-resolved point dose measurements.Criteria were defined to assess whether errors would cause a clinically relevant dose deviation during patient treatment. The sensitivity and specificity were determined based on verification measurements of five error-free plans and 84 intentional error plans. Receiver operator characteristic analysis was conducted to quantify the efficiency of the method. In addition, the specificity of the method was investigated in more detail by assessing its ability to identify different error modes.For measurements made at planning target volume locations, a moderate sensitivity (65% ± 13%), specificity (76% ± 12%), and an area under the curve (AUC) equal to 0.77 were obtained for a quality control (QC) acceptance criterion of 2%. Measurements made at organ at risk (OAR) locations had high sensitivity (80% ± 20%), but low specificity (54% ± 13%), and an AUC equal to 0.70. The low specificity for OAR locations could be traced to the impact of a small couch tilt on measurement locations at larger distances from the isocentre, resulting in increased shielding by multi-leaf collimator (MLC) leaves.Further analysis showed that output errors and errors affecting the penumbra region can be resolved on a per measurement basis with moderate to high sensitivity (100% and 67% for errors in output, and in the penumbra region, respectively) and high specificity (77% and 85% for errors in output, and in the penumbra region, respectively). This can potentially result in saving time investigating failing QC measurements.

DotCode Damage Testing

The DotCode bar code symbology is relatively new, having been developed by Dr. Andrew Longacre in 2007. As a result of standards organization work being done on the symbology, it was determined that valid encoding patterns could result in symbols that could not be decoded by the current reference decode algorithm. A solution for resolving the issue involved the introduction of intentional errors that rely on the correct functioning of the Reed-Solomon Error Correction (RSEC) to resolve the original message. However, the actual impacts of such a decision were publicly unknown. This paper has undertaken the task of validating the impacts of intentionally adding additional data bits to the bar code, resulting in the generation of errors in what should otherwise be perfect symbols.

Quality assurance of geometric accuracy based on an electronic portal imaging device and log data analysis for Dynamic WaveArc irradiation.

The purpose of this study was to develop a simple verification method for the routine quality assurance (QA) of Dynamic WaveArc (DWA) irradiation using electronic portal imaging device (EPID) images and log data analysis. First, an automatic calibration method utilizing the outermost multileaf collimator (MLC) slits was developed to correct the misalignment between the center of the EPID and the beam axis. Moreover, to verify the detection accuracy of the MLC position according to the EPID images, various positions of the MLC with intentional errors in the range 0.1–1 mm were assessed. Second, to validate the geometric accuracy during DWA irradiation, tests were designed in consideration of three indices. Test 1 evaluated the accuracy of the MLC position. Test 2 assessed dose output consistency with variable dose rate (160–400 MU/min), gantry speed (2.2–6°/s), and ring speed (0.5–2.7°/s). Test 3 validated dose output consistency with variable values of the above parameters plus MLC speed (1.6–4.2 cm/s). All tests were delivered to the EPID and compared with those obtained using a stationary radiation beam with a 0° gantry angle. Irradiation log data were recorded simultaneously. The 0.1‐mm intentional error on the MLC position could be detected by the EPID, which is smaller than the EPID pixel size. In Test 1, the MLC slit widths agreed within 0.20 mm of their exposed values. The averaged root‐mean‐square error (RMSE) of the dose outputs was less than 0.8% in Test 2 and Test 3. Using log data analysis in Test 3, the RMSE between the planned and recorded data was 0.1 mm, 0.12°, and 0.07° for the MLC position, gantry angle, and ring angle, respectively. The proposed method is useful for routine QA of the accuracy of DWA.

УЧЕТ ИНДИВИДУАЛЬНО-ПСИХОЛОГИЧЕСКИХ ОСОБЕННОСТЕЙ ПЛАВАТЕЛЬНОГО СОСТАВА И ВЛИЯНИЕ ЧЕЛОВЕЧЕСКОГО ФАКТОРА НА БЕЗОПАСНОСТЬ ТРАНСПОРТНОГО ПРОЦЕССА

The article examines the influence of the human factor on the safety of the transportation process, as well as individual psychological traits of the ship’s crew. The human factor that causes crashes and incidents at sea can be defined as the actions or omissions of the crew members, as well as intentional or unintentional human errors which affect the operation of the system or performance of a specific task. In the world practice, various measures are used to reduce the impact of the human factor on the safety of navigation at sea. Such measures include additional training and practice of crew members on board and on shore, rationing the rest hours, etc. The measures under consideration are strictly registered by the regulatory framework, with respect to ensuring the safety of navigation. At the same time, these measures do not allow to effectively consider the individual psychological traits of the crew members. Increasing the level of professional training of ship crews, due to technical improvements on board the ship, requires the development and implementation of measures that allow for the individual psychological characteristics of the seagoing personnel. Taking account of competence and experience in psychology, human engineering, physiology, ergonomics and medicine in transport there have been worked out measures for reducing the human factor. Special attention is paid to the activities which help training specialists possessing the required competences (qualification skills). The proposed activities will allow forming a staff selection system for the navy.

Impact of awareness about hypertension on compliance to antihypertensive medication

Background: Hypertension, a common cardiovascular disorder accounts for 20-50% of all deaths. This risk can be greatly ameliorated by creating awareness about disease and its effective treatment alongside regular medical check-ups. Therapeutic failures result from patient non-compliance, manifested as intentional or unintentional errors in dosage or schedule, overuse or underuse of prescribed drugs and early termination of therapy. Adherence is helpful for management of hypertension and cost minimization. Non-adherence to the drug treatment is an important factor for uncontrolled hypertension and its complications.Methods: Patients were interviewed individually after taking informed consent, using pretested, predesigned, self- administered and closed ended questionnaire both before and 4 weeks after creating awareness about hypertension and its complications. Compliance measured by self-reporting in which knowledge of the patient about number of antihypertensive drugs being used, formulations of drugs, frequency of administration, duration of taking the drugs and knowledge of complications due to uncontrolled and untreated hypertension were assigned 1 score each. Patient having score of at least 4 out of total 5 was considered compliant.Results: No significant association of compliance with demographic and other variables like age, sex, marital status, economic status, education, urbanization, duration of treatment and drug procurement were noted. A significant increase in compliance in patients on antihypertensive medication was found 4 weeks after creating awareness about hypertension and its complication. A significant increase in compliance scores was also seen in non-compliant patients showing their shifting from non-compliance to compliance group. Overall compliance increased from 59.38% to 84.38%. A percentage decrease from 58.82% to 25% in patients having uncontrolled hypertension was also observed after the awareness about hypertension.Conclusions: Demographic variables, duration of hypertension and drug procurement have no significant effect on compliance to antihypertensive medication. There is persistence and improvement in compliance to antihypertensive medications after an education of the patients about hypertension and its complications.

El error inexcusable en la legislación Ecuatoriana.

La presente investigación se ha desarrollado sobre el error inexcusable y la serie de sanciones para el Juez que incurre en éste, que, a entender de muchos juristas, rebasa en drasticidad, pues para que el error sea inexcusable tiene que reunir las condiciones contenidas en el mentado artículo 109 del Código Orgánico de la Función Judicial, es decir que el error debe contener un dolo, manifiesta negligencia y error inexcusable. El Estado, a sus conciudadanos a través de su máxima ley, debe protegerlos, debe ampararlos, respetar sus derechos, de tal manera que todas las personas estemos cobijamos por la seguridad jurídica, es por eso que el proceso que ampara estos derechos debe estar revestido de esta condición, es decir, que el judicial que las funge de juez constitucional acierte en su decisión para amparar estos derechos. Esta es la premisa principal, el Juez dada su versación jurídica constitucional, está en la obligación de acertar su decisión. Pero, ¿qué pasa cuando esta decisión está errada porque el operador de justicia constitucional tuvo una diferente visión del problema a él encomendado a resolverlo y cae en el error?, el legislador, fácilmente ha insertado entre las sanciones disciplinarias del referido error inexcusable, que en la mayoría de los casos ha conllevado a la destitución del servidor.

Improving the gamma analysis comparison using an unbinned multivariate test

In this study, we present a new procedure for the comparison of two dose matrices by means of a statistical test. A statistical distance is proposed to decide whether the difference between the two matrices is statistically significant. This statistical test is based on the square difference between the experimental and expected gamma matrix results. The expected gamma matrix is calculated by simulating the measurement process. For comparison purposes, the significance level of the test was chosen to give the same statistical significance as 90% of gamma-pass rate. The performance of the statistical distance is checked against 53 VMAT. The power of the presented test was compared using simulations with the 90% gamma-pass rate criteria for two cases in which intentional errors are introduced. In both cases, the test is uniformly more powerful. According to the test, two of the measured plans have a significant difference with calculated matrices, although the gamma pass rate measured was always greater than 90%.

Clinical implementation of an exit detector-based dose reconstruction tool for helical tomotherapy delivery quality assurance.

The aim of this study was to validate the accuracy of an exit detector-based dose reconstruction tool for helical tomotherapy (HT) delivery quality assurance (DQA). Exit detector-based DQA tool was developed for patient-specific HT treatment verification. The tool performs a dose reconstruction on the planning image using the sinogram measured by the HT exit detector with no objects in the beam (i.e., static couch), and compares the reconstructed dose to the planned dose. Vendor supplied (three "TomoPhant") plans with a cylindrical solid water ("cheese") phantom were used for validation. Each "TomoPhant" plan was modified with intentional multileaf collimator leaf open time (MLC LOT) errors to assess the sensitivity and robustness of this tool. Four scenarios were tested; leaf 32 was "stuck open," leaf 42 was "stuck open," random leaf LOT was closed first by mean values of 2% and then 4%. A static couch DQA procedure was then run five times (once with the unmodified sinogram and four times with modified sinograms) for each of the three "TomoPhant" treatment plans. First, the original optimized delivery plan was compared with the original machine agnostic delivery plan, then the original optimized plans with a known modification applied (intentional MLC LOT error) were compared to the corresponding error plan exit detector measurements. An absolute dose comparison between calculated and ion chamber (A1SL, Standard Imaging, Inc., WI, USA) measured dose was performed for the unmodified "TomoPhant" plans. A 3D gamma evaluation (2%/2mm global) was performed by comparing the planned dose ("original planned dose" for unmodified plans and "adjusted planned dose" for each intentional error) to exit detector-reconstructed dose for all three "Tomophant" plans. Finally, DQA for 119 clinical (treatment length <25cm) and three cranio-spinal irradiation (CSI) plans were measured with both the ArcCHECK phantom (Sun Nuclear Corp., Melbourne, FL, USA) and the exit detector DQA tool to assess the time required for DQA and similarity between two methods. The measured ion chamber dose agreed to within 1.5% of the reconstructed dose computed by the exit detector DQA tool on a cheese phantom for all unmodified "Tomophant" plans. Excellent agreement in gamma pass rate (>95%) was observed between the planned and reconstructed dose for all "Tomophant" plans considered using the tool. The gamma pass rate from 119 clinical plan DQA measurements was 94.9%±1.5% and 91.9%±4.37% for the exit detector DQA tool and ArcCHECK phantom measurements (P=0.81), respectively. For the clinical plans (treatment length <25cm), the average time required to perform DQA was 24.7±3.5 and 39.5±4.5min using the exit detector QA tool and ArcCHECK phantom, respectively, whereas the average time required for the 3 CSI treatments was 35±3.5 and 90±5.2min, respectively. The exit detector tool has been demonstrated to be faster for performing the DQA with equivalent sensitivity for detecting MLC LOT errors relative to a conventional phantom-based QA method. In addition, comprehensive MLC performance evaluation and features of reconstructed dose provide additional insight into understanding DQA failures and the clinical relevance of DQA results.

Shared pilot passage plan and navigational safety during pilotage

Navigating in confined waters with a pilot aboard requires that the pilot’s intention and plan is understood by all present on the bridge. The present study investigates the effect of having a detailed route plan and monitoring it in the context of pilotage. The aim was to see how the presence of a shared pilot passage plan in the Electronic Chart Display and Information System (ECDIS) affects the identification and recovery from navigational errors made by a pilot. Twenty participants, 10 with a shared route plan and 10 without, participated as navigators in a simulator scenario involving pilotage in the Oslofjord. Participants were bachelor students in nautical science. The navigation scenarios involved the intentional error by the pilot just before a predefined way point. Three measurements of relevance to navigational safety were recorded: (1) the time it took the participant to express concern, (2) the time it took the participant to correct the error (‘time to recovery’), and (3) the number of groundings. The study revealed that time to express concern and time to recovery were significantly much shorter for the group with a shared pilot passage plan presented in ECDIS than for the group without such a plan. Providing a bridge team with a shared pilot passage plan in ECDIS during pilotage might improve the ability to identify and correct navigational errors.

The legal understanding of intentional medical error

The paper is devoted to doctor, a professional and humanist who dedicated himself to medicine and is committed to lifelong learning, ethics and assistance to victims, even against their express consent. The theme is focused on the problem of intentional medical error in order to negate it in the context that the conscientious doctors should be protected from tort and free of moral burden. This paper seeks to answer the question, if the error represents a doctor's failure to the detriment of the user (patient), how should we treat his attempt, made professionally and with the best intentions, regardless of the fatal outcome? In addition, medical-legal theory and practice beside intentional medical mistake mention also the unintentional, whose formation does not require any kind of responsibility because the doctor's behavior in that case was not inconsistent with medical ethics, standards and rules. In this regard, the author's research was based on the following questions: is there a deliberate medical error, who is ready to knowingly endanger the patient by doing medical procedures contrary to the rules (neglect, avoidance of assistance, misdiagnosis, improper treatment, indifference, discrimination), who is competent to qualify the taken action as an error (intentional, unintentional) and what evidences are required for the brutal attack on the integrity of top experts, that will be charged and prosecuted? Literature abounds with assertions that medical errors are as old as medicine, which is not true. Also, it is incorrect to say that it had appeared for the first time in the middle of the nineteenth century. That would be a roughly canceling of ancient medical marking, bearing in mind that even before the mentioned period, there had been a very successful medicine with high quality doctors and their brilliant achievements, but also with illnesses and dead persons. As far the data on the exact occurrence of medical errors are considered, the numerous authors claim that it does not have to be communicated, since it is placed in the field of history, that unlike many science is not exact, and should not always be considered as reliable. Any medical error makes a multiple interests, firstly of the researchers in the true sense of the word, and secondly, of the sensationalist columnists. The latter see the culprit only in the doctor, because many of them never presented the scene when defeated doctor leaves the Service ambulance, clinic, emergency room or any other health care area, because the most terrible thing in the profession has happened -the lost of a patient. Sensationalists are rarely present when despair and tears are being replaced by joy, smile and exaltation. They do not understand that it is impossible to meet the doctor who will be prepared to deliberately violate the profession, ethical values, Hippocratic oath, to directly endanger the health or life of the patient, or make a deliberate mistake and commit an offense.

Impact of Jaw Position Accuracy on Dose Variation in Volumetric Modulated Arc Therapy Using Jaw Tracking.

The technique of jaw tracking can be used in volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT). In this technique, jaw tracks apertures of the multi leaf collimator (MLC) during irradiation. It is reported that dose variation is occurred by the changing accuracy of MLC position in VMAT and IMRT. Though jaw moves dynamically in the irradiation by using this technique, the influence of the jaw position accuracy on dose variation is not examined. The purpose of this study is to verify the influence of jaw position accuracy on dose variation in VMAT using jaw tracking. We appended intentional errors on jaw position in digital image communication in medicine-radiation therapy (DICOM-RT) plans created using jaw tracking technique. These plans were irradiated on the phantom that was inserted ion chamber, and we measured dose variation by changing the intentional error. The dose variation in planning target volume (PTV) was enlarged by increasing the error, and agreed with the variation of a collimator scatter factor within 0.03%. In clinical case of oropharyngeal cancer, the maximum dose variations in parotid gland were 0.179% and 1.23% when the errors were 1 mm and 10 mm, respectively. Dose variation in parotid gland was larger than the variation in PTV and spinal cord because of increasing MLC transmission. The dose variation caused by jaw position error was smaller than it caused by MLC position error. So, we can keep the dose error slightly that is related to jaw position error in VMAT by maintaining jaw position accuracy correctly.

Research on two methods for improving the axial static and dynamic characteristics of hydrostatic lead screws

This paper researches two methods for improving the axial static and dynamic characteristics of hydrostatic lead screws, i.e. (a) using membrane restrictor instead of capillary restrictor and (b) utilizing the intentional periodic pitch errors in the nut to generate hydrodynamic effect of the lubricating film. The Reynolds’ equation, which is applicable to the lubricating film in hydrostatic lead screws, is deduced based on the equivalent plane of the flank surface of threads. The perturbation technique and the finite difference method are used to obtain the static and dynamic characteristics. The JFO boundary condition is used for capturing the cavitation. The results show that the axial static and dynamic characteristics can gain a marked improvement by combining the two methods.

Guidelines for reproducing geometrical aspects of intra-oral radiographs images on cone-beam computed tomography

Human identification requires comparison of individual traits of a person, depending on the availability and reproduction of antemortem (AM) records. If there is no presumed identity or AM exams are not available for comparison, the production of postmortem (PM) records is impaired. The purpose of this research is to describe and test standards to enable the comparison of antemortem periapical radiographs to images extracted from the manipulation of postmortem CBCT exams in multiple identification simulations in a randomized blind study. In a simulation, 20 CBCT images from dry skulls were used as PM records and 3 periapical radiographs (total of 60) that were randomized and blinded from the first examiner. In each case, an intentional incidence error of 10° was added in four different directions. Three points were selected in the AM radiograph, and the angle, linear measurements and proportion between these distances were collected. The AM data were used to mathematically find similar image geometry on a CBCT maximum intensity projection. Possible identification by superimposition was achieved in all cases, and statistical analysis proved the success in the reproduction of angular and length proportion using CBCT incidence manipulation. Significant reproducibility was also observed on intra- and inter-observer tests. In conclusion, the images extracted from CBCT could be compared to any periapical radiographs by superimposition, providing acceptable evidence to establish human identification. The application of this protocol is suitable for forensic practices with the high level of reproducibility and could be used as PM record when no AM records are available at the time of the exam.

Validation of the Mobius system for patient-specific quality assurance using introduced intentional errors.

Mobius3D and MobiusFX are model-based verification tools for treatment plan dose calculation and treatment delivery. The software facilitates patient-specific quality assurance by extracting data from linear accelerator treatment log files and performing a 3D dose calculation on the original patient CT dataset using an independent collapsed cone algorithm. In this study, we evaluate the ability of the Mobius system to detect linear accelerator-related errors compared with existing measurement-based systems, namely the ArcCHECK® and 3DVH® systems. Three original treatment plans and 47 plans with introduced delivery errors, for a total of 50 plan deliveries, were investigated. The results from this study demonstrated comparable gamma passing rates and error detectability between the Mobius and ArcCHECK® systems while the 3DVH system generally exhibited a lower sensitivity. This work also demonstrated the ability of the Mobius system to detect delivery errors of down to 2° collimator rotation, 1mm MLC bank offset and 10mm collimator jaw offset.

The effects of consecutive night shifts and shift length on cognitive performance and sleepiness: a field study

Introduction. The aim of this study was to evaluate the effects of consecutive night shifts (CNS) and shift length on cognitive performance and sleepiness. Materials and methods. This study evaluated the sleepiness and performance of 30 control room operators (CROs) working in 7 nights, 7 days, 7 days off (7N7D7O) and 30 CROs working in 4 nights, 7 days, 3 nights, 7 days off (4N7D3N7O) shift patterns in a petrochemical complex on the last night shift before swinging into the day shift. To assess cognitive performance, the n-back test, continuous performance test and simple reaction time test were employed. To assess sleepiness, the Karolinska sleepiness scale was used. Results. Both schedules indicated that the correct responses and response times of working memory were reduced (p = 0.001), while intentional errors and sleepiness increased during the shift work (p = 0.001). CNS had a significant impact on reaction time and commission errors (p = 0.001). Conclusion. The main duty of CROs at a petrochemical plant is checking hazardous processes which require appropriate alertness and cognitive performance. As a result, planning for appropriate working hours and suitable number of CNS in a rotating shift system is a contribution to improving CRO performance and enhancing safety.

Automatic detection of MLC relative position errors for VMAT using the EPID-based picket fence test

Multi-leaf collimators (MLCs) ensure the accurate delivery of treatments requiring complex beam fluences like intensity modulated radiotherapy and volumetric modulated arc therapy. The purpose of this work is to automate the detection of MLC relative position errors ⩾0.5 mm using electronic portal imaging device-based picket fence tests and compare the results to the qualitative assessment currently in use. Picket fence tests with and without intentional MLC errors were measured weekly on three Varian linacs. The picket fence images analysed covered a time period ranging between 14–20 months depending on the linac. An algorithm was developed that calculated the MLC error for each leaf-pair present in the picket fence images. The baseline error distributions of each linac were characterised for an initial period of 6 months and compared with the intentional MLC errors using statistical metrics. The distributions of median and one-sample Kolmogorov–Smirnov test p-value exhibited no overlap between baseline and intentional errors and were used retrospectively to automatically detect MLC errors in routine clinical practice. Agreement was found between the MLC errors detected by the automatic method and the fault reports during clinical use, as well as interventions for MLC repair and calibration. In conclusion the method presented provides for full automation of MLC quality assurance, based on individual linac performance characteristics. The use of the automatic method has been shown to provide early warning for MLC errors that resulted in clinical downtime.

Impact of Tooth Indexing Errors on Dynamic Factors of Spur Gears: Experiments and Model Simulations

This paper investigates the influences of tooth indexing errors on dynamic factors of spur gears. An experimental study is performed using root strain measurements to (i) establish baseline dynamic behavior of gears having negligible indexing errors and (ii) characterize changes caused by tightly controlled intentional indexing errors to this baseline dynamic behavior. For this, test gears having different forms of indexing errors are paired with an instrumented gear having negligible indexing error. Dynamic root strains of teeth in the neighborhood of teeth with indexing error are measured. A dynamic gear load distribution model is employed to simulate these experiments. Both measurements and predictions indicate clearly that the baseline dynamic response, dominated by well-defined resonance peaks, is altered significantly by transient vibrations induced by indexing errors, in the process increasing dynamic factors significantly in comparison to the case of negligible indexing error.

Cryptanalysis of McEliece cryptosystem variants based on quasi‐cyclic low‐density parity check codes

One of the approaches to modify the McEliece cryptosystem to overcome its large key size is replacing binary Goppa codes with a new structured code. However, this modification makes such cryptosystems encounter some new attacks. There are a few modified McEliece cryptosystem variants which are known to be secure. One of them is the cryptosystem introduced by Baldi et al. which uses quasi-cyclic low-density parity check (QC-LDPC) codes. This cryptosystem is still unbroken as no efficient attack has been reported against it since 2008. In this study, an attack has been applied to this cryptosystem which is feasible when the code length is a multiple of a power of 2. Also an important weakness of this kind of cryptosystem has been pointed out, namely utilising a too low-weight intentional error vector. The authors have established a new security level for this cryptosystem which is applicable to other McEliece-like cryptosystems using QC-LDPC codes. This security level for instance is 29.18 times lower than previous ones in the case of n = 4 x 4096 when only one ciphertext is available. The gain of the attack in this study can be increased if more than one ciphertext is available.

SU‐F‐T‐230: A Simple Method to Assess Accuracy of Dynamic Wave Arc Irradiation Using An Electronic Portal Imaging Device and Log Files

Purpose:The Dynamic Wave Arc (DWA) technique, where the multi‐leaf collimator (MLC) and gantry/ring move simultaneously in a predefined non‐coplanar trajectory, has been developed on the Vero4DRT. The aim of this study is to develop a simple method for quality assurance of DWA delivery using an electronic portal imaging device (EPID) measurements and log files analysis.Methods:The Vero4DRT has an EPID on the beam axis, the resolution of which is 0.18 mm/pixel at the isocenter plane. EPID images were acquired automatically. To verify the detection accuracy of the MLC position by EPID images, the MLC position with intentional errors was assessed. Tests were designed considering three factors: (1) accuracy of the MLC position (2) dose output consistency with variable dose rate (160–400 MU/min), gantry speed (2.4–6°/s), ring speed (0.5–2.5°/s), and (3) MLC speed (1.6–4.2 cm/s). All the patterns were delivered to the EPID and compared with those obtained with a stationary radiation beam with a 0° gantry angle. The irradiation log, including the MLC position and gantry/ring angle, were recorded simultaneously. To perform independent checks of the machine accuracy, the MLC position and gantry/ring angle position were assessed using log files.Results:0.1 mm intentional error can be detected by the EPID, which is smaller than the EPID pixel size. The dose outputs with different conditions of the dose rate and gantry/ring speed and MLC speed showed good agreement, with a root mean square (RMS) error of 0.76%. The RMS error between the detected and recorded data were 0.1 mm for the MLC position, 0.12° for the gantry angle, and 0.07° for the ring angle.Conclusion:The MLC position and dose outputs in variable conditions during DWA irradiation can be easily detected using EPID measurements and log file analysis. The proposed method is useful for routine verification.This research is (partially) supported by the Practical Research for Innovative Cancer Control (15Ack0106151h0001) from Japan Agency for Medical Research and development, AMED. Authors Takashi Mizowaki and Masahiro Hiraoka have consultancy agreement with Mitsubishi Heavy Industries, Ltd., Japan.

TU‐H‐207A‐02: Relative Importance of the Various Factors Influencing the Accuracy of Monte Carlo Simulated CT Dose Index

Purpose:Monte Carlo simulation is a frequently used technique for assessing patient dose in CT. The accuracy of a Monte Carlo program is often validated using the standard CT dose index (CTDI) phantoms by comparing simulated and measured CTDI100. To achieve good agreement, many input parameters in the simulation (e.g., energy spectrum and effective beam width) need to be determined. However, not all the parameters have equal importance. Our aim was to assess the relative importance of the various factors that influence the accuracy of simulated CTDI100.Methods:A Monte Carlo program previously validated for a clinical CT system was used to simulate CTDI100. For the standard CTDI phantoms (32 and 16 cm in diameter), CTDI100 values from central and four peripheral locations at 70 and 120 kVp were first simulated using a set of reference input parameter values (treated as the truth). To emulate the situation in which the input parameter values used by the researcher may deviate from the truth, additional simulations were performed in which intentional errors were introduced into the input parameters, the effects of which on simulated CTDI100 were analyzed.Results:At 38.4‐mm collimation, errors in effective beam width up to 5.0 mm showed negligible effects on simulated CTDI100 (&lt;1.0%). Likewise, errors in acrylic density of up to 0.01 g/cm3 resulted in small CTDI100 errors (&lt;2.5%). In contrast, errors in spectral HVL produced more significant effects: slight deviations (±0.2 mm Al) produced errors up to 4.4%, whereas more extreme deviations (±1.4 mm Al) produced errors as high as 25.9%. Lastly, ignoring the CT table introduced errors up to 13.9%.Conclusion:Monte Carlo simulated CTDI100 is insensitive to errors in effective beam width and acrylic density. However, they are sensitive to errors in spectral HVL. To obtain accurate results, the CT table should not be ignored.This work was supported by a Faculty Research and Development Award from Cleveland State University.