IAEA TECDOC 1517 Quality Control in Mammography Software

Transcription

1 IAEA TECDOC 1517 Quality Control in Mammography Software Fredy Somarriba a, Patricia Mora b*, Margarita Chevalier c and Raul Ramirez d a Universidad Nacional Autónoma de Nicaragua, Managua, Nicaragua. b Centro de Investigación en Ciencias Atómicas, Nucleares y Moleculares, Universidad de Costa Rica, Costa Rica. c Facultad de Medicina, Universidad Complutense, Madrid, España. d Radiological Protection of Patients Unit, Department of Nuclear Safety and Security, IAEA. Abstract. In October 2006, the IAEA published the TECDOC 1517 Quality Control in Mammography, whose main purpose was to give Latin American countries a protocol in Spanish with all necessary QC. This protocol harmonizes the tests and evaluation criteria of mammography equipment and its complementary equipment; it states the different responsibilities on all personnel and gives guidance on radiographic techniques. It was the joint effort of two ARCAL projects: RLA/6/043 and RLA/9/035. QC programs are needed to assure the final quality of mammography images and to optimize the radiation dose to the patients. Countries where national campaigns are used to improve the early detection of breast cancer among asymptomatic women require the establishment of QC programs. Specific software has been developed based on the TECDOC 1517 to facilitate the technologist, medical physicist and physician its implementation. It has a main menu bar tool and icons for rapid access to the different tests. The help option in each test pops a window with the same procedure written on the TECDOC for the user s convenience. The tests are divided on the same sections as in the document: visual inspection, storage of films, dark room, image system, radiological equipment, automatic exposure control, geometry, collimation, image visualization, film rejection analysis, image quality and dosimetry. On each test, data is introduced on specific color cells and when the user activates the calculation button, the results are compared against its tolerance levels, and indication of pass/fail is finally displayed. This software, available to all Member States, adds extra value to the TECDOC 1517 since errors in calculations will be reduced by its use. It will harmonize the way results are presented, it will facilitate comparisons, it reduces the time to evaluate the results of the test and finally it becomes a teaching tool for the TECDOC. KEYWORDS: mammography, quality control, software, TECDOC Introduction Breast cancer is the most common cancer among women worldwide and is a leading cause of cancer mortality in women. Breast cancer incidence increased per cent from the 1970s to the 1990s in most countries, with the most marked increases among women aged fifty years and older, although the incidence for women under fifty is increasing. Mammography is an X ray examination of the breast. Its principal purpose is to facilitate the detection of breast cancer at a point earlier in its natural history than possible by clinical examination. It has been demonstrated that routine screening with high quality mammography is effective in reducing mortality from breast cancer in women aged [1-2] One of the key elements to obtain a high quality mammogram is the establishment of a Quality Control (QC) program.[3-4] In 2006, the International Atomic Energy Agency (IAEA) published the IAEA TECDOC-1517 Quality Control in Mammography.[5] This document in Spanish was the joint effort of two ARCAL projects: RLA/6/043 and RLA/9/035; with the participation of the following countries: Argentina, Bolivia, Brazil, Chile, Colombia, Costa Rica, Cuba, Guatemala, El Salvador, Mexico, Nicaragua, Panamá, Paraguay, Perú, República Dominicana and Venezuela. This protocol harmonizes the tests and evaluation criteria of mammography equipment and its complementary equipment such as the processor; it states the different responsibilities on all personnel on a mammography facility and gives guidance on radiographic techniques. It is aimed to help optimize radiation doses in mammography [6] and provide a teaching material for the different personnel. patricia.mora@ucr.ac.cr

2 The software was developed for the Latin American mammography community to reduce calculation errors, harmonize the way results are presented, facilitate comparison among national professionals and with colleagues of other countries, reduce the time necessary to evaluate the test results and finally to become a teaching tool for the TECDOC General overview of the program The Principal Screen has a standard menu bar with a list of the entire QC tests to perform; see Figure 1. It also has a second bar with icons for easy access to each test. There are a total of 29 windows for each of the tests described in the IAEA TECDOC In each window all mathematical formulas have been introduced and are automatically calculated for easy comparison of the result with the tolerance value of the test. Each window can be saved or printed. Figure 1: Principal Screen Four different colors for easy identification of the purpose of the cells were used in all windows; see Figure 2. Light gray is used for fixed cells or cells displaying tolerance values. White cells are used by the user to introduce data to the software (either alphabetic or numerical values). Dark gray cells are used to perform calculations by the software and their results are showed on yellow cells. Figure 2: Use of different colors for cells in the program 2

3 During the execution of a window, the program can show 4 sub windows for: additional information, confirmation of an action, error message or warning message. The user moves through a window with the TAB button or positioning the mouse on a specific cell. Menu Files are managed as in other Windows based programs with icons for new, open, save, print and exit options. Once the Institution name has been added on the first window it will appear on all pages of the report. A general report can be printed with all the windows or individual prints can be done for each test. On Figure 3 an example of one of the reports generated is presented. Figure 3: Visual inspection of the x-ray mammography unit report. On the main tool bar a Help option will give the user a short manual with instructions on installation, programs designed and a general description on all QC tests. Also available for convenience of the user, on each window a Help icon will bring the text of the specific test as presented on the IAEA TECDOC Figure 4 shows an example of the help window. 3

4 Figure 4: Help window 3. Description of the windows Institution data: on this first window the user is asked to introduce the information on the x-ray mammography equipment, processor and film used at the facility being evaluated, also, information on the person doing the tests. Visual inspection: a simple table with YES/NO entries must be completed; it can be seen on Figure 3. Storage of films: an evaluation on the storage conditions of the films is done. Dark room evaluation: this window evaluates the general conditions of the darkroom, (such as temperature and humidity), light leakage and fog due to safety lights. Processor: ph of developer and fixer, processing time, replenishment rate and artifacts are evaluated with this window. Sensitometry: three different windows are used for sensitometric purposes. The first one establishes the initial operation levels (IOL) for the base + fog, low density, mid density and high density. The second window is the daily sensitometric test. As data is added everyday, a graphic representation of base + fog, mid density and density difference is displayed; as shown on Figure 5. Finally on a separate window a calculation is performed when a transition between boxes is done. 4

5 Figure 5: Sensitometric data window with associated graphics Image system: it contains the test for screen cleanness and screen-film contact. Screen tightness and uniformity: for all used cassettes spots are looked for and if found, recorded on the window. Also values of mas and OD are recorded for each screen to evaluate their uniformity among them. The following tests due to their recommended frequency and required equipment will be performed by the medical physicist (except those related to the mammographic phantom and film rejection rate). When an ionization chamber has to be used all windows will ask if the chamber corrects for temperature and pressure; if not, introduction of temperature and pressure is necessary to have the software calculate the correction factor. It is important to be aware of the units for different magnitudes (for example, µgy or mgy depending on the test). Also many cells have a choice of values to choose; for example, anode/filter combination, compression (yes/no), etc. Careful understanding of the following tests is necessary in order to use the software correctly. Radiation leakage: Using the measured air kerma rates at the points where leakage has been found, the software will extrapolate a value in msv/hr to compare to the regulatory 1 msv/hr at 1 meter value. kvp: this window will evaluate the accuracy of 7 nominal values of kvp and its repeatability at 28 kvp and Mo/Mo combination. Compliance with the tolerance values will be done when the button Conform is pressed. An example of this test is shown in Figure 6. 5

6 Figure 6: Kilovoltage evaluation test window Half value layer: establishment of the HVL will be done for reference conditions (e.g. 28 kvp and Mo/Mo) and for 3 clinical conditions set by the user based on the institution preference. For each filter condition 3 readings have to be entered. Output: again the output will be calculated for the reference conditions (e.g. 28 kvp and Mo/Mo) and for 2 user conditions. For 4 values of mas, 5 readings are needed to calculate the output, its linearity and repeatability. Time: for those units where the time is displayed after the exposure, the accuracy and repeatability will be calculated. Compression force: in this window the user has to indicate the units of the force (N, Lb or kg) and record the compression force for manual and automatic modes. Automatic Exposure Control (AEC): this window evaluates the repeatability of the AEC and its compensation for different thickness of the breast and beam quality. Density control setting evaluation: the user will obtain images for all the density control settings and comparison of the OD and mas values with the tolerance values will be established. Collimation system: this window contains several tests, first it verifies that the SID is > 60 cm, then a general overview of the collimation system is done by evaluation of coincidence between the radiation field and the image receptor; the coincidence between the light field and the radiation field and finally the alignment of the compression paddle with the margin of the breast support. View boxes: a general visual inspection of view boxes is done, followed by luminance measurements at 9 points in each view box. Then if more than one view box is used a comparison between them is carried out based on the central luminance of each panel. Room ambient illumination is also evaluated. In Figure 7 an example of the evaluation of view boxes and room ambient illumination window is shown. 6

7 Figure 7: View Box and Room ambient illumination window Film rejection rate: a simple evaluation chart for film rejection analysis is presented to be filled out. Common factors for film rejection are sorted by technique factors (e.g. movement, wrong marking, etc.) and darkroom and processor factors (e.g. fog). Image: this window contains the phantom image evaluation (using the known scoring system of fibers, masses and microcalcification groups) and the spatial resolution of the system. Incident air kerma and Mean Glandular Dose: there are 2 equal windows for this test, one for the reference condition and one for clinical conditions. The user has to pick if the x-ray equipment shows the mas after the exposure in order for the software to use the appropriate formulas. The formulas take into account the c DG50,Ki,PMMA factor that converts the entrance air kerma to the mean glandular dose for a 45 mm thick standard phantom and the corresponding s factor which gives a correction that depends on the target/filter combination. [7-8] Figure 8 shows an example of this window. 7

8 Figure 8: Window for Incident Kerma and Mean glandular dose calculation 4. Conclusions Most of the quality control protocols include data form sheets to illustrate how data must be taken by the technologist, medical physicist or radiologist. However, the lack of a complete definition or a glossary about the magnitudes linked to their tolerance values give rise to a wide spread of results. [9-10] This fact causes misunderstandings when the results on the applicability of the protocols are compared. This software has the main objective of harmonizing results which is of special importance for several reasons: First, mammography is a very compromising radiological examination since it is used to detect early breast cancer. As it is well known, the diagnostic signs linked to its early detection rely on fine details whose visualization imposes important requirements (for example high contrast and resolution, and low noise) to the whole mammographic imaging chain. On the other hand, early breast cancer programs are directed to asymptomatic women, where the benefit could be overcome by the risk of delivering high doses to the women. Therefore, image quality and dose values have to be strictly verified and optimized by applying the adequate quality control procedures. [11] Second, it will facilitate comparison among national professionals and with colleagues of other countries. These comparisons have been demonstrated to be an important element in the optimization process of the mammographic image acquisition technique. Third, in those countries where there is no tradition in the implementation of the quality control programs, the comparison of results can help to detect failure on the application of the protocol. In this way, the software can also be understood as a helpful tool to learn about quality control. 8

9 Finally, it reduces the time to evaluate the results of the numerous tests on the TECDOC This is very important since the number of medical physicists or technologists in Latin America in diagnostic medical physics involved in quality control tasks are usually very low or even inexistent. In consequence, when these professionals are engaged in QC programs, they are in charge of a high number of different radiological equipment. REFERENCES [1] WORLD HEALTH ORGANIZATION, IARC Handbooks of Cancer Prevention, Vol 7: Breast Cancer Screening, (INTERNATIONAL AGENCY FOR RESEARCH ON CANCER ed.), IARC Press, Lyons (2002). [2] TABAR, L., et al., Mammography service screening and mortality in breast cancer patients: 20 year follow up before and after introduction of screening, Lancet 361 (2003) [3] AMERICAN COLLEGE OF RADIOLOGY, Mammography Quality Control Manual, ACR, New York (1999). [4] AMERICAN ASSOCIATION OF PHYSICISTS IN MEDICINE, Equipment requirements and quality control for mammography, Report No. 29, American Institute of Physics, New York (1990). [5] INTERNATIONAL ATOMIC ENERGY AGENCY, TEC DOC 1517 Control de Calidad en Mamografía, Viena (2006). [6] INTERNATIONAL ATOMIC ENERGY AGENCY, International Basic Safety Standards for Protection Against Ionizing Radiation and for the Safety of Radiation Sources, Safety Series No. 115, Vienna (1996). [7] DANCE, D.R., Monte Carlo calculation of conversion factors for the estimation of mean glandular breast dose, Phys. Med. Biol., 35 (1990) [8] EUROPEAN COMMISSION, European Protocol on Dosimetry in Mammography, CEC- Report EUR 16263, Office for Official Publications of the European Communities, Luxembourg (1996). [9] EUROPEAN COMMISSION, European Guidelines for Quality Assurance in Mammography Screening, 3 rd Edition, Europe Against Cancer, Office for Official Publications of the European Communities, Luxembourg (2001). [10] EUROPEAN COMMISSION, European Guidelines for Quality Assurance in Breast Cancer screening and diagnosis. 4 th Edition, European Communities, Belgium (2006). [11] SOCIEDAD ESPAÑOLA DE FÍSICA MÉDICA-SOCIEDAD ESPAÑOLA DE PROTECCIÓN RADIOLÓGICA, Protocolo Español de Control de Calidad en Radiodiagnóstico (Aspectos Técnicos), Edicomplet, Madrid (1996). 9