Sigma Index Research Articles

Interest and limits of the six sigma methodology in medical laboratory.

The mandatory accreditation of clinical laboratories in France provides an incentive to develop real tools to measure performance management methods and to optimize the management of internal quality controls. Six sigma methodology is an approach commonly applied to software quality management and discussed in numerous publications. This paper discusses the primary factors that influence the sigma index (the choice of the total allowable error, the approach used to address bias) and compares the performance of different analyzers on the basis of the sigma index. Six sigma strategy can be applied to the policy management of internal quality control in a laboratory and demonstrates through a comparison of four analyzers that there is no single superior analyzer in clinical chemistry. Similar sigma results are obtained using approaches toward bias based on the EQAS or the IQC. The main difficulty in using the six sigma methodology lies in the absence of official guidelines for the definition of the total error acceptable. Despite this drawback, our comparison study suggests that difficulties with defined analytes do not vary with the analyzer used.

VLF/LF Amplitude Perturbations before Tuscany Earthquakes, 2013

The US Navy VLF/LF Transmitter’s NSY signal (45.9 kHz) transmitted from Niscemi, Sicily, Italy, and received at the Kiel Long Wave Monitor, Germany, was analyzed for the period of two months, May and June (EQ-month) of 2013. There were 12 earthquakes of magnitude greater than 4 that hit Italy in these two months, of which the earthquake of 21st June having magnitude of 5.2 and a shallow focal depth of 5 km was the major one. We studied the earthquake of 21st of June 2013, which struck Tuscany, Central Italy, (44.1713°N and 10.2082°E) at 10:33 UT, and also analyzed the effects of this earthquake on the sub-ionos- pheric VLF/LF signals. In addition, we also studied another earthquake, of magnitude 4.9, which hit the same place at 14:40 UT on 30th of June and had shallow focal depth of 10 km. We assessed the data using terminator time (TT) method and night time fluctuation method and found unusual changes in VLF/LF amplitudes/phases. Analysis of trend, night time dispersion, and night time fluctuation was also carried and several anomalies were detected. Most ionospheric perturbations in these parameters were found in the month of June, from few days to few weeks prior to the earthquakes. Moreover, we filtered the possible effects due to geomagnetic storms, auroras, and solar activities using parameters like Dst index, AE index, and Kp index for analyzing the geomagnetic effects, and Bz (sigma) index, sunspot numbers, and solar index F10.7 for analyzing the solar activities for the confirmation of anomalies as precursors.

Dosimetric study of RapidArc plans and conventional intensity modulated radiotherapy for prostate cancer involving seminal vesicles and pelvis lymph nodes

Purpose: The main purpose of this study is to (1) identify the continual diversity between conventional fixed field intensity modulation radiotherapy (IMRT) and RapidArc (RA) for high-risk prostate cancer; and (2) determine potential benefits and drawbacks of using for this type of treatment. Methods: A cohort of 20 prostate cases including prostate, seminal vesicles and pelvic lymph nodes was selected for this study. The primary planning target volume (PTV P ) and boost planning target volume (PTV B ) were contoured. The total prescription dose was 75.6 Gy (45 Gy to PTV P and an additional 21.6 Gy to PTV B ). Two plans were generated for each PTV: multiple 7-fields for IMRT and two arcs for RA. Results: A Sigma index (IMRT: 2.75 ± 0.581; RA: 2.8 ± 0.738) for PTV P and (IMRT: 2.0 ± 0.484; RA: 2.1 ± 0.464) for PTV B indicated similar dose homogeneity inside the PTV. Conformity index (IMRT: 0.96 ± 0.047; RA: 0.95 ± 0.059) for PTV P and (IMRT: 0.97 ± 0.015; RA: 0.96 ± 0.014) for PTV B was comparable for both the techniques. IMRT offered lower mean dose to organ at risks (OARs) compared to RA plans. Normal tissue integral dose in IMRT plan resulted 0.87% lower than RA plans. All the plans displayed significant increase (2.50 times for PTV P and 1.72 for PTB B ) in the average number of necessary monitor units (MUs) with IMRT beam. Treatment delivery time of RA was 2 ‒ 6 minutes shorter than IMRT treatment. Conclusion: For PTV including pelvic lymph nodes, seminal vesicles and prostate, IMRT offered a greater degree of OARs sparing. For PTV including seminal vesicles and prostate, RA with two arcs provided comparable plan with IMRT. RA also improved the treatment efficiency due to smaller number of MUs required.

Dosimetric study of RapidArc plans with flattened beam (FB) and flattening filter-free (FFF) beam for localized prostate cancer based on physical indices

Purpose: To identify the continual diversity between flattening photon beam (FB) and Flattening Filter Free (FFF) photon beams for localized prostate cancer; and to determine potential benefits and drawbacks of using unflattened beam for this type of treatment. Methods : Eight prostate cases including seminal vesicles selected for this study. The primary planning target volume (PTV P ) and boost planning target volume (PTV B ) were contoured. The total prescription dose was 78 Gy (56 Gy to PTV P and an additional 22 Gy to PTVB). For all cases, treatment plans using 6MV with FB and FFF beams with identical dose-volume constraints, arc angles and number of arcs were developed. The dose volume histograms for both techniques were compared for primary target volume and critical structures. Results: A low Sigma index (FFF: 1.65 + 0.361; FB: 1.725 + 0.39) indicating improved dose homogeneity in FFF beam. Conformity index (FFF: 0.994 + 0.01; FB: 0.993 + 0.01) is comparable for both techniques. Minimal difference of Organ at risk mean dose was observed. Normal tissue integral dose in FB plan resulted 1.5% lower than FFF plan. All the plans displayed significant increase (1.18 times for PTV P and 1.11 for PTB B ) in the average number of necessary MU with FFF beam. Conclusion : Diversity between FB and FFF beam plans were found. FFF beam accelerator has been utilized to develop clinically acceptable Rapid Arc treatment plans for prostate cancer with 6 MV. --------------------------------- Cite this article as : Rout BK, Muralidhar KR, Ali M, Shekar MC, Kumar A. Dosimetric study of RapidArc plans with flattened beam (FB) and flattening filter-free (FFF) beam for localized prostate cancer based on physical indices. Int J Cancer Ther Oncol 2014; 2 (4):02046. DOI : 10.14319/ijcto.0204.6

A Study on the Development of Service 6 Sigma Index in Service Industry by using the Bootstrapped Method

A Study on the Development of Service 6 Sigma Index in Service Industry by using the Bootstrapped Method

Quantitative comparison of volumetric modulated arc therapy and intensity modulated radiotherapy plan quality in sino-nasal cancer

The aim of this study was to compare various dosimetric parameters of dynamic mlc intensity modulated radiotherapy (IMRT) plans with volumetric modulated arc therapy (VMAT) plans for sino-nasal cancers, which are rare and complex tumors to treat with radiotherapy. IMRT using five fields, coplanar in the sagittal plane and VMAT employing two coplanar arc plans were created for five patients. The plans were assessed by comparing Conformity Index and Sigma Index (dose homogeneity) in the Planning Target Volume (PTV) and through comparison of dose-volume characteristics to the following organs at risk (OARs): Spinal cord, brainstem, eye, ipsilateral and contralateral optic nerve and the volume of brain receiving 10% of the prescribed dose (V10%). The total monitor units required to deliver the plan were also compared. Conformity Index was found to be superior in VMAT plans for three patients and in IMRT plans for two patients. Dose homogeneity within the PTV was better with VMAT plans for all five cases. The mean difference in Sigma Index was 0.68%. There was no significant difference in dose between IMRT and VMAT plans for any of the OARs assessed in these patients. The monitor units were significantly reduced in the VMAT plan in comparison to the IMRT plan for four out of five patients, with mean reduction of 66%. It was found in this study that for the treatment of sino-nasal cancer, VMAT produced minimal, and statistically insignificant improvement in dose homogeneity within the PTV when compared with IMRT. VMAT plans were delivered using significantly fewer monitor units. We conclude in this study that VMAT does not offer significant improvement of treatment for sino-nasal cancer over the existing IMRT techniques, but the findings may change with a larger sample of patients in this rare condition.

Benchmarking Dosimetric Quality Assessment of Prostate Intensity-Modulated Radiotherapy

To benchmark the dosimetric quality assessment of prostate intensity-modulated radiotherapy and determine whether the quality is influenced by disease or treatment factors. We retrospectively analyzed the data from 155 consecutive men treated radically for prostate cancer using intensity-modulated radiotherapy to 78 Gy between January 2007 and March 2009 across six radiotherapy treatment centers. The plan quality was determined by the measures of coverage, homogeneity, and conformity. Tumor coverage was measured using the planning target volume (PTV) receiving 95% and 100% of the prescribed dose (V(95%) and V(100%), respectively) and the clinical target volume (CTV) receiving 95% and 100% of the prescribed dose. Homogeneity was measured using the sigma index of the PTV and CTV. Conformity was measured using the lesion coverage factor, healthy tissue conformity index, and the conformity number. Multivariate regression models were created to determine the relationship between these and T stage, risk status, androgen deprivation therapy use, treatment center, planning system, and treatment date. The largest discriminatory measurements of coverage, homogeneity, and conformity were the PTV V(95%), PTV sigma index, and conformity number. The mean PTV V(95%) was 92.5% (95% confidence interval, 91.3-93.7%). The mean PTV sigma index was 2.10 Gy (95% confidence interval, 1.90-2.20). The mean conformity number was 0.78 (95% confidence interval, 0.76-0.79). The treatment center independently influenced the coverage, homogeneity, and conformity (all p < .0001). The planning system independently influenced homogeneity (p = .038) and conformity (p = .021). The treatment date independently influenced the PTV V(95%) only, with it being better at the start (p = .013). Risk status, T stage, and the use of androgen deprivation therapy did not influence any aspect of plan quality. Our study has benchmarked measures of coverage, homogeneity, and conformity for the treatment of prostate cancer using IMRT. The differences seen between centers and planning systems and the coverage deterioration over time highlight the need for every center to determine their own benchmarks and apply clinical vigilance with respect to maintaining these through quality assurance.

Development and comparison of four sleep spindle detection methods

The objective of the present work was to develop and compare methods for automatic detection of bilateral sleep spindles. All-night sleep electroencephalographic (EEG) recordings of 12 healthy subjects with a median age of 40 years were studied. The data contained 6043 visually scored bilateral spindles occurring in frontopolar or central brain location. In the present work a new sigma index for spindle detection was developed, based on the fast Fourier transform (FFT) spectrum, aiming at approximating our previous fuzzy spindle detector. The sigma index was complemented with spindle amplitude analysis, based on finite impulse response (FIR) filtering, to form of a combination detector of bilateral spindles. In this combination detector, the spindle amplitude distribution of each recording was estimated and used to tune two different amplitude thresholds. This combination detector was compared to bilaterally extracted sigma indexes and fuzzy detections, which aim to be independent of absolute spindle amplitudes. As a fourth method a fixed spindle amplitude detector was included. The combination detector provided the best overall performance; in S2 sleep a 70% true positive rate was reached with a specificity of 98.6%, and a false-positive rate of 32%. The bilateral sigma indexes provided the second best results, followed by fuzzy detector, while the fixed amplitude detector provided the poorest results so that in S2 sleep a 70% true positive rate was reached with a specificity of 97.7% and false-positive rate of 46%. The spindle amplitude distributions automatically determined for each recording by the combination detector were compared to amplitudes of visually scored spindles and they proved to correspond well. Inter-hemispheric amplitude variation of visually scored bilateral spindles is also presented. Flexibility is beneficial in the detection of bilateral spindles. The present work advances automated spindle detection and increases the knowledge of bilateral sleep spindle characteristics.

Rheological analysis and quantitative evaluation of wet kneaded wax matrix.

The properties of the wet kneaded wax matrix were evaluated using a compression tester, whereby a newly proposed sigma index for the plastic deformation was assessed in the pressure transmission diagram. The sigma index was indicative of a characteristic of the plastic yield point in the rheological behavior, and presented an initial and abrupt deformation of wet kneaded mass when the wet kneaded mass was subjected to the pressure. The value of sigma index was confirmed to decrease along with an increase in the plasticity of wet kneaded mass. The wet mass of wax matrix was prepared under various kneading time, and then extruded. The properties of the extruded granules such as pore volume, strength and dissolution were investigated. As a result, it was found that the sigma index decreased with an increase in kneading time. The granules with small value of sigma index showed few porosities, large strength and slow dissolution. It was demonstrated that the sigma index linked the characteristics of wet kneaded mass to the dissolution and the other granule properties. Existence of this link was revealed by sigma index evaluation relevant to the plasticity. The sigma index could be a decisive criterion to permit an in-process evaluation of the kneading progress quantitatively, and also useful for anticipating the dissolution of the final granules roughly.

A Common Denominator for Test Scores

In recent issue of the Elementary School Journal appeared an article' describing briefly some uses can be made of the sigma index score as standard measuring unit. The purpose of the present article is to give full indorsement to the use of this statistical device and to attempt an explanation of its merits in measuring instructional outcomes. It is generally conceded mental age and achievement age mean different things in different tests. Franzen concluded a child may have mental age of 14 and reading age of 12 and an arithmetic age of 13 and still he may have done exactly as well on the arithmetic test and on the reading test as he has done on the intelligence test provided the three tests have different correlations with age. Wilson also contends that mental or educational age is often misleading unit for use in comparing an individual's score on one test with his score on another test.3

The Sigma Index Score as a Standard Measuring Unit

Previous articleNext article No AccessThe Sigma Index Score as a Standard Measuring UnitJ. T. WorltonJ. T. Worlton Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Elementary School Journal Volume 30, Number 5Jan., 1930 Article DOIhttps://doi.org/10.1086/456418 Views: 2Total views on this site PDF download Crossref reports no articles citing this article.

The Inconstancy of the IQ as Measured by Repeated Group Tests

The study of the growth of school children which is being conducted at the Psycho-Educational Clinic at Harvard University, under the direction of Professor Walter F. Dearborn, has completed its sixth year. During this time a large number of children have been given two or three intelligence tests each year. The material that has been compiled from the results of these tests gives an excellent opportunity for the study of the constancy, or inconstancy, of the intelligence quotient as measured by the same and different group tests. The variation of the IQ was discussed in this journal,1 where it was claimed that inconstancy necessarily resulted from the technique of its calculation whenever the quotient was more than a few points above or below 100, and that this error might be avoided by the use of a scale based on standard deviations. The present paper begins with a study of the gains in IQ at the median and quartile points of groups when the same test is repeated at yearly intervals, and closes with a compari son of the results obtained by the IQ technique and those that would result from the sigma index technique suggested by the above authors. The subjects were selected from a larger group which included all the children from an average community, a suburb of Boston, who were in the first or second grade in 1922-23. This selection included all the children, of North European descent, for whom a record of an Otis test was available for four successive years, a Dearborn test for five or six. years, and who were either six or seven years of age when they took the first test.2

When Is a Failure Not a Failure?

Early in the present school year the teachers were asked for lists of the pupils who were failing in their courses. The reports showed a total of ten failing pupils in the ninth grade. In an attempt to determine why these pupils were failing, they were given the Terman Group Test of Mental Ability. This test was followed by the Thorndike-McCall Reading Scale, the WoodyMcCall Mixed Fundamentals, and the Morrison-McCall Spelling Scale. In the case of each pupil the results of these tests were reduced to common denominations by converting them into sigma indices, which were then recorded on a Sigma Index Record Card. The card thus showed what the pupil had done in each subject in terms of what he was capable of doing. The record of one pupil was as follows: intelligence, 84; reading, 83; spelling, 89; mixed fundamentals, 85; and arithmetic reasoning, 84. It is evident that while this pupil was doing unsatisfactory work as compared with the average pupil, he was doing as well as could be expected of a pupil of his capacity. This is shown by the fact that the results of his accomplishment tests were parallel with the results of his intelligence test. This record is typical of the records of the other nine pupils. Thus it is seen that when these pupils were compared with the average pupil of the class they were failures, just as the teachers reported them. On the other hand, when each pupil's accomplishments were compared with his capacity, it is seen that he had done satisfactory work.