Multiple Detectors Computerized Tomography Scan - Research Proposal Example

School of Population Health Population Health Honours Dissertation Proposal The role of Automatic Exposure Control in reduction MDCT radiation dose of chest and abdomen procedures Name: ___________________ Student Number: __________________ Supervisor: _______________________ Synopsis: Background: As the issues regarding the radiation exposure from Computerized Tomography remain prevalent, Multiple-Detectors Computerized Tomography (MDCT) became a latest breakthrough in diagnostic imaging. Concerns with radiation exposure prompt the development of reducing dose, one of which is AEC, which requires further research, especially with the use in children, to ensure the safety of the procedure for paediatric patients. Objective: To identify the role of Automatic Exposure Control (AEC) in reduction of Multiple Detectors Computerized Tomography scan (MDCT) radiation dose regarding its use, benefits and appropriateness in chest and abdomen procedures for paediatric patients. Research plan: A retrospective, co-relational, non-experimental phase II clinical trial will investigate paediatric patients who undergone MDCT on the chest and abdominal area and analyze their exposure to radiation dose using CTDI and DLP in relation with the use of AEC. Data will undergo t-test, Pearson’s r and ANOVA. Role of AEC will be identified based from the obtained data analysis. Statement of the Aim The overall aim of this project is to identify the role of Automatic Exposure Control (AEC) in reduction of Multiple Detectors Computerized Tomography scan (MDCT) radiation dose regarding its use, benefits and appropriateness in chest and abdomen procedures for paediatric patients. Objectives 1. To investigate the use of Automatic Exposure Control in reducing the exposure dose in chest examinations of paediatric patients. 2. To examine the effectiveness of different Automatic Exposure Control systems of various manufacturers of Multiple Detectors Computerized Tomography apparatuses. 3. To identify the best protocol and Automatic Exposure Control techniques for all manufacturers of Multiple Detectors Computerized Tomography apparatuses in minimizing the radiation dose for paediatric patients. 4. To determine potential standardisation of Automated Exposure Control techniques in Computerized Tomography imaging modality for effective dose reduction. Benefits of the Study This study hopes to provide further understanding to this newly-innovated MDCT technology, particularly about public concerns on the increasing medical radiation exposure mainly from CT scans, more specifically about its use in children who are more vulnerable than adults in radiation exposure. Should AEC be proven to be a safe and effective way in reducing radiation dose, this would give assurance to patients that the benefits of this procedure heavily outweigh the risks involved If AEC does not, this study will further warrant other researchers to either enhance the available AEC, or look for another safe and effective approach in reducing radiation dose by MDCT scanning. Literature Review Multiple-Detectors Computerized Tomography (MDCT) Multiple-Detectors Computerized Tomography (MDCT) is a diagnostic procedure as an improvisation of the standard single-slice computerized tomography. It is considered to be the greatest advancement of diagnostic imaging (Rubin, 2003). Known to be useful in vascular and cardiac conditions, MDCT extends its applicability to diagnose abdominal, pelvic, thoracic and head and neck abnormalities. Compared to single-slice CT scanning, it provides better imaging quality, faster scanning times, reduction of the need of sedation, and lower dose of radiation when used appropriately. The use of the device is known to be useful in paediatric patients. It comes with various slice options: ranging from 2 up to 256 slices per revolution, depending on the device. Some of the manufacturers of MDCT devices are Siemens, Lightspeed VCT, General Electric Technologies and Philips Medical Systems (Kalra et al., 2006). Compared to single-slice CT scanning, the images generated by Multiple-Detectors Computerized Tomography provide a better three-dimensional (3D) image (Prokop, 2003). Usefulness of MDCT In cardiology, MDCT provided a reliable assessment of the heart’s left ventricular volume and mass (Schlosser et al, 2005). It is able to provide accurate detection of coronary artery disease without the need to manipulate the patient’s heart rate (Ghersin et al, 2006). In pulmonary medicine, its usefulness in detecting pulmonary embolism was observed (Eyer, Goodman and Washington, 2005). In urology, it was found out to be a promising technique in detection of urinary tract neoplasm (Caoili et al, 2005). These are just few examples of the potential applicability of MDCT. Radiation Exposure in MDCT The issue about radiation exposure was still present regarding the use of MDCT. Increased radiation dose of computerized tomography procedures is a concern as it was being used continuously for decades (Lee et al, 2010). Computerized tomography scanning was among the top contributor of medical radiation exposures in the United States (Mettler et al, 2006). Mini et al (1995) investigated on the radiation dose delivered in a standard CT examination of the trunk and found out that the values of the absorbed radiation are high compared to x-ray examinations, and suggested to keep CT scans as low as possible. Even though MDCT procedure can allow a more minimal exposure to radiation than the standard CT procedure, Kalra et al (2006) noted its potential abuse and inappropriateness, especially when the device is not appropriately used. To minimize the potential risks of radiation exposure, the “As Low As Reasonably Achievable” philosophy must be observed (Einstein et al, 2007). Automatic Exposure Control (AEC) for MDCT Automatic Exposure Control is one of the radiation dose-reduction techniques in computerized tomography. The device works by modulating the radiation intensity emitted by MDCT in relation to patient’s size, “z-axis thickness” and “angular thickness” (Lee et al, 2010). The device will respond once it reaches the threshold set by the operator. This device will limit the dose that is more than necessary to obtain the image quality enough for making an accurate diagnosis. When used properly, it is a useful device for optimisation of dose, but still, further research is required (Guđjónsdóttir, Ween and Olsen, 2010). Measurement of Radiation Dose in MDCT Scan There are several methods in measuring radiation dose (dosimetry). Radiation exposure measures the ionized radiation in air (expressed in Coulombs per kilogram or C/kg), yet not useful in CT. Absorbed dose measures how much radiation was absorbed by the object or organ (expressed in gray or Gy in SI units, equivalent to 100 rad in conventional units), while the effective dose will estimate the radiation of the body as a whole when radiation was exposed only locally (expressed in Sievert or Sv). Since it was not possible to measure the absorbed dose inside a patient, a scale that estimates radiation exposure was formulated, known as the Computerized Tomography Dose Index or CTDI and the Dose-Length Product or DLP (Mayo, Aldrich and Muller, 2003). 1. Computerized Tomography Dose Index (CTDI) CTDI is the mostly used standard parameter in measuring and estimating the average radiation dose per slice from CT scans (Bauhs et al, 2008; Kalra et al, 2004). The measurement uses a 100-mm docimeter in PMMA (polymethyl methacrylate) phantom as standard. Unit is in mGy. CTDI100 = (1/nT) ∫ D(z)dz n = no. of slices T = slice thickness D(z) = radiation dose Weighted CTDI was introduced to more accurately measure the radiation dose of the whole body. CTDIw = (1/3) CTDI + (2/3) CTDI However, since the measurements obtained in CTDI is only an approximation of individual patient dose and does not consider other important parameters such as patient size, weight, shape,, proportion, composition and overall parameter, it’s not completely accurate (Bauhs et al, 2008; Fearon, 2002), even if it was further developed into a re-scaled Volume CT dose index or CTDIvol (Gutierrez et al, 2007). Despite the limitations of the CTDI, it is the globally accepted system in evaluating radiation dose of patients (Bauhs et al, 2008). 2. Dose Length Product (DLP) DLP measures the total radiation dose exposure after completing the whole series of CT scan. The formula of DLP is multiplying the CTDI to the length of irradiation (unit is in mGy x cm). Since its value is dependent to CTDI, it shares the same inaccuracy of CTDI, yet no other more accurate tests are available to be used in living patients. Paediatric Considerations in MDCT While there are potential risks behind radiation doses to adults, more emphasis must be placed on the critical importance of limiting the dose of paediatric patients undergoing MDCT (Frush et al, 2002). Babies and children are more sensitive to radiation exposure, more vulnerable to effects of radiation (Bernhardt, Lendi and Deinzer, 2006). It is possible to limit the dose to as minimum value without deteriorating the image quality (Kamael et al, 1994). Strategies to limit the radiation dose received by paediatric patients are: doing it only if necessary, limiting the exposed region and adjustment of client-based settings (Frush, Donnelly and Rosen, 2003). Nevertheless, Even if with the use of AECs, further research is needed to assure the safety of MDCT in children (Guđjónsdóttir, Ween and Olsen, 2010). Use of AEC on MDCT in dose reduction Brisse et al (2009) compared the radiation doses of organs with automated exposure control with the non-usage of automated exposure control to a phantom equivalent to a newborn, 1-year-old, 5-year-old, and 10-year-old child, and found out the dose decrease on thyroid, lung, oesophagus and breast, but an increase in salivary glands, bladder and ovaries, so they suggested taking first consideration regarding the use of AEC in children. Summary of Literature Review As MDCT emerge as a new technology, only a few studies are available about the dose reduction in MDCT by AEC, especially in children. Further research with the use of AEC in MDCT is necessary to ensure the safety of the procedure for paediatric patients. Research Plan Description of Population and Sample The data to be gathered for this study shall be taken from the target population (P): all cases of MDCT involving paediatric patients admitted at England-based hospitals. Each individual case is not based from the number of patients undergoing the procedure, but every instance the procedure was made within the sampling period. Some patients may have multiple instances of MDCT within the period of data gathering, whether it be on the same hospital or another; thereby one patient can have one or more separate cases, and patients will not be identified by their names. This is one way of ensuring the participant’s privacy. The sampling period will depend on the length of time given by the supervisor to the researcher. For instance, the sampling period shall be 5 months. It is not necessary to gather fresh data during the sampling period, so the study will go retrogressively. The sampling period will be within 5 months of all patients undergoing MDCT from 01 January 2009 to 30 June 2010. The target population shall be named according to 1) hospital code, 2) the hospital number of the patient and 3) the date the procedure was done (in ddmmyy format). For example, a case of a patient admitted at Northwick Park Hospital (coded 209) with hospital number 123456 who had undergone MDCT last 25 October 2008 shall be named “209-123456-251008”. If in case the same patient had a repeat MDCT on 04 January 2009 at Hammersmith Hospital (coded 067) wherein he had a different hospital code at this hospital, for example, 987654, the case name will be “067-987654-040109”. Cases 209-123456-251008 and 067-987654-040109 shall be treated differently even if both cases refer only to an individual patient. However, same patient cases that happened at a hospital beyond the hospital sample of the study will be excluded. To gather the target population, a sampling frame is needed. There must be first a sampling frame of all hospitals operating at England within the sampling period of research, the target hospital population (PHospital). However, the accessible population will be dependent on the researcher’s budget, so it is possible to have only one hospital as the sample hospital. Inclusion criteria for the sample hospital/s are: must have a fully-operational and utilized MDCT, at least one case of patient undergoing MDCT, and if the research study will be allowed by the hospital administration. Thereby, a hospital which stopped its MDCT operation on the middle of the sampling period shall also be included in the study. After the identification of a accessible hospital population meeting the inclusion criteria, the sample hospital/s shall be selected using simple random sampling, and is based from the budget and available tome of the researcher to conduct the study. Those hospitals passing the inclusion criteria will undergo a lottery method, and the hospitals shall be drawn out in a sequential order. The sequential order of the hospitals drawn shall be the baseline in selecting the accessible sample hospital (NHospital), wherein the selection begins from the top of the list, until the desired hospital sampling size was attained. After attaining the sample hospital/s to be used in the study, the sample population of cases (N) will be taken. A sampling frame of all cases of patients undergoing MDCT within the sampling period will be attained from the roster of the previously-identified hospital sample. Inclusion criteria are: paediatric patients (age 0 to 18 years old within the sampling period), and who had undergone MDCT within the sampling period, and that the MDCT procedure was performed within the chest and abdomen area. A case of an 18-year old patient who had undergone MDCT at the first month of the study will be included, but the case of the same patient having a birthday within the sampling period and undergoes another MDCT in his 19th birthday at the 4th month will be excluded. All cases gathered from different sample hospitals shall be collated. Like the sampling method used in attaining the sample hospital population, after meeting the inclusion criteria, the collated sample cases to be used (n) shall be selected using simple random sampling by undergoing a lottery method until the desired sampling size was obtained. The cases obtained from the sampling method will be used as the database for this study. Definition of variables The variables to be used in the study are based from Bongartz et al’s Chapter 3 Appendix I of European Guidelines on Quality Criteria for Computed Tomography, but modified to serve the purpose of the study in determination of the role of AEC in dose reduction in MDCT. Demographic data are the coded name of case (see Description of Population and Sample), age, sex, height and weight. The independent variable lies mainly whether there is use of AEC or not (yes or no) and the phantom diameter. The dependent variables necessary for this study are the normalized weighted CTDI (nCTDIw), weighted CTDI (CTDIw), dose-length product (DLP), total dose-length product. Computation for CTDI and DLP is no longer necessary since it is indicated in the roster of MDCT procedures available at hospital records. Other data to be gathered are: MDCT scanner manufacturer and type, year of manufacture, patient position (supine, prone, others), gantry tilt (none; cranial, degree; caudal, degree) Laser camera manufacturer/type, in use since (date) Film manufacturer/type Film Processor manufacturer/type, processing time, developer Temperature Image viewing settings: reconstruction algorithm, field of view, window width, window level Exposure factors, tube voltage, tube current exposure time, tube current total acquisition time, slice thickness, couch increment (table feed), number of slices (for serial scanning and for helical scanning) Statistical methods Objective 1: To identify the significant dose reduction of AEC Bivariate statistical test will be used to identify any dose reduction done by AEC to MDCT procedure. Group A have cases which utilizes AEC, while Group B cases do not utilize AEC. The mean, median and mode, range and the standard deviation of the values of nCTDIw, CTDIw, DLP and total dose-length product will be identified, compared and will be represented in a series of tables for each dependent variable, and will be analyzed using t-test. Table 1. Sample Table for Normalized Weighted CTDI (mSv) using Fictitious Data Group A (with AEC) Group B (without AEC) 8.9 8.3 9.7 9.4 11.8 13.4 10.7 12.2 10.9 11.5 Objective 2: To identify dose reduction factors beyond the use of AEC It is possible to have another variable other than the use of AEC that would influence the dose reduction in MDCT. It is possible that age, sex, height and weight influence the reduction of dose. For this reason, each variable will undergo their respective test statistics. Pearson’s r will analyze interval and ratio variables (e.g. age vs. nCTDIw) while nominal variables will undergo analysis of variance (ANOVA) (e.g. MDCT scanner manufacturer and type vs. nCTDIw). Ethical Considerations Since this study is a retrospective, co-relational, non-experimental Phase II clinical trial, ethics approval is not required in this study. However, proper research conduct like confidentiality must be observed. The use of name coding of the hospitals and the patients will further ensure patient’s privacy and maintain hospital’s confidential information. Budget This study does not necessitate funding from the School of Population Health, but might cover additional travel expenses aside from computing, printing and photocopying, yet depends on the researcher’s willingness to reach as many hospitals as possible. Statement of Participation The researcher will do most of the work in this study. However, the researcher can ask for assistance from each hospital’s records department staff to assist the researcher in providing the data needed by this study. Timetable The entire duration of this study is from 1 June 2010 to 1 November 2010. 1 Jun 2010 1 Jul 2010 1 Aug 2010 1 Sep 2010 1 Oct 2010 1 Nov 2010 Formatting Dissertation Writing Diss. Presentation Writing Results & Discussion Prepration of Results Writing methods Writing Introduction Interpretation of Results Data Analysis Data Cleansing Proposal Submission Literature Review Project Duration Figure 1: A Gantt chart of the study timeline. REFERENCES Bauhs et al. 2008, ‘CT dosimetry: comparison of measurement techniques and devices.’ Radiographics, vol. 28 pp. 245–53. Bernhardt, P., Lendl, M. & Deinzer, F., 2006, ‘New technologies to reduce pediatric radiation doses’, Pediatric Radiology, vol. 36 pp. 212-215. Bongartz, G. et al., 2008, ‘European guidelines on quality criteria for computed tomography’, http://www.drs.dk/guidelines/ct/quality/mainindex.htm, last modified 27 October 2008, Brisse, H. et al., 2009, ‘Assessment of Organ Absorbed Doses and Estimation of Effective Doses From Pediatric Anthropomorphic Phantom Measurements for Multi-Detector Row CT With and Without Automatic Exposure Control’, Health Physics, vol. 97 pp. 303-314. Caoili, E. et al., 2005, ‘MDCT Urography of Upper Tract Urothelial Neoplasms,’ American Journal of Roetgenology, vol. 184 pp. 1873-1881. Einstein, A. et al. 2007, ‘Radiation Dose to Patients from Cardiac Diagnostic Imaging: Contemporary Reviews in Cardiovascular Medicine’, Circulation, vol. 116 pp. 1290-1305. Eyer, B., Goodman, L. & Washington, L., 2005, ‘Clinicians Response to Radiologists Reports of Isolated Subsegmental Pulmonary Embolism or Inconclusive Interpretation of Pulmonary Embolism Using MDCT’, American Journal of Roetgenology, vol. 184 pp. 623-628. Fearon, T., 2002, ‘CT dose parameters and their limitations,’ Pediatric Radiology, vol. 32 pp. 246-249. Frush, D.., Donnelly, L. and Rosen, N., 2003, ‘Computed Tomography and Radiation Risks: What Pediatric Health Care Providers Should Know’, Pediatrics, vol. 112 pp. 951-957. Frush, D. et al., 2002, ‘Computer-Simulated Radiation Dose Reduction for Abdominal Multidetector CT of Pediatric Patients,’ American Journal of Roetgenology, vol. 179 pp. 1107-13. Ghersin, E. et al, 2006, ‘16-MDCT Coronary Angiography Versus Invasive Coronary Angiography in Acute Chest Pain Syndrome: A Blinded Prospective Study,’ American Journal of Roetgenology, vol. 186 pp. 177-184. Guđjónsdóttir, J., Ween, B. & Olsen, D., 2010, ‘Optimal Use of AEC in CT: A Literature Review,’ Radiologic Technology, vol. 81 pp. 309-317. Guttierez, D. et al., 2007, ‘CT-automatic exposure control devices: What are their performances?’, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, vol. 580 pp. 990-995. Kalra M. et al, 2004, ‘Multidetector Computed Tomography Technology: Current Status and Emerging Developments’, Journal of Computer Assisted Tomography, vol. 28 pp. S2-S6. Kalra, M. et al., 2006, MDCT: From Protocols to Practice. Springer, New York. Kamael et al., 1994, ‘Radiation dose reduction in CT of the pediatric pelvis.’ Radiology, vol. 190 pp. 683-687. Lee, K. et al., 2010, “Dose Reduction And Image Quality Assessment In MDCT Using AEC (D-DOM & Z-DOM) And In-Plane Bismuth Shielding,’ Radiation Protection Dosimetry. Mini et al., 1995, ‘Radiation exposure of patients who undergo CT of the trunk,’ Radiology, vol. 195 pp. 557-562. Mettler, F. et al., 2008, ‘Medical Radiation Exposure in the U.S. in 2006: Preliminary Results,’ Health Physics, vol. 95 pp. 502-507. Prokop, M., 2003, ‘General principles of MDCT’, Bracco Symposium on MDCT, vol. 45 p. 94. Rubin, G., 2003, ‘MDCT: a new era in imaging,’ European Radiology Supplements, vol. 16 pp. 3-10. Schlosser, T. et al, 2005, ‘Assessment of Left Ventricular Parameters Using 16-MDCT and New Software for Endocardial and Epicardial Border Delineation,’ American Journal of Roetgenology vol. 184 pp. 765-773. Read More