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Ensuring safety in transition to digital radiography in practice Kwan-Hoong Ng, PhD President, AFOMP University of Malaya, Kuala Lumpur, Malaysia KH Ng 1. Introduction 2. Advantages of going digital 3. Issues in going digital 4. Strategies in monitoring dose 5. Strategies in dose management 6. Summary KH Ng 1. Introduction KH Ng “ While digital techniques have the potential to reduce patient doses, they also have the potential to significantly increase them.” - ICRP 93 Editorial KH Ng “This is a technology that is advancing rapidly and which will soon affect hundreds of millions of patients. If careful attention is not paid to the radiation protection issues of digital radiology, medical exposure of patients will increase significantly and without concurrent benefit.” - ICRP 93 Editorial KH Ng • Most principles for dose reduction for screen-film radiography, especially justification, are relevant to digital systems • However, in digital systems different scenarios apply for dose reduction and optimisation compared with screen-film radiography KH Ng 2. Advantages of going digital KH Ng Screen-Film Radiography Digital Radiography Recording Digital detector Displaying Display Monitor Archiving PACS server Major limitation is ‘film’ Optimize each component independently KH Ng • The diagnostic information provided by modern digital detectors can be equal or superior to conventional screen-film systems, with comparable patient doses. • Digital imaging has practical technical advantages compared with film techniques, e.g. wide contrast dynamic range, post-processing functions, multiple image viewing options, and electronic transfer and archiving possibilities. KH Ng 3. Issues in going digital KH Ng “This is a technology that is advancing rapidly and which will soon affect hundreds of millions of patients. If careful attention is not paid to the radiation protection issues of digital radiology, medical exposure of patients will increase significantly and without concurrent benefit.” [We are witnessing the consequences now] - ICRP 93 Editorial KH Ng KH Ng Digital imaging brings benefits but also demands changes in ways of working Digital x ray imaging involves issues cost and productivity, need to acquire new skills, radiation doses, overuse, image quality. It is easy to delete digital images, and repeat exposures normally go undetected. Ng BMJ 2006 Different imaging tasks require different levels of image quality. e.g. the follow-up examination for a fracture does not require the same image quality as that required for its diagnosis. Ng BMJ 2006 Current safety issues with clinical digital radiography: Technology Factors • Automatic Exposure Control (AEC) • Exposure (sensitivity) index KH Ng AEC The wide exposure dynamic range of such systems may have the disadvantage that, if the X-ray generator AEC develops a fault or the output calibration drifts, the dose increase/decrease may not be identified readily. Also, the wide exposure dynamic range means there is significant potential for the initial set-up of such systems not to be optimised. KH Ng AEC Digital radiography systems may have different X-ray energy responses to screen-film systems. Therefore the generator's AEC compensation characteristics should be different from that used for screen-film systems. For existing systems which have been upgraded to CR or DR, the existing AEC compensation characteristics will need reprogramming. X-ray equipment manufacturers should work with physicists on this. Exposure (sensitivity) Index Each image should ideally have an associated number to indicate the level of exposure to the detector. Currently all digital systems have a exposure (sensitivity) index which is related to detector exposure. Once digital radiography systems are in use, the constancy of applied exposure factors should be monitored on a regular basis. List of terms for exposure indices for various digital systems and their relationship to traditional dose measure (in µGy). In the 2nd column the proposal for an international standardisation is detailed (courtesy of Ulrich Neitzel, Philips Medical Systems, Hamburg). Uffmann et al E J Radiol 72 (2009) 202–208 Am J Roentgenol. 2012 Dec;199(6):1337-41 Both the IEC (IEC standard 62494-1) and the AAPM (AAPM Task Group 116) have developed similar standards for monitoring exposure in digital radiography to eliminate proprietary and confusing terminology. Radiologists and technologists will need to learn three new terms - exposure index, target exposure index, and deviation index - to understand the new standards. Current safety issues with clinical digital radiography: Human Factors • • • • Inappropriate exposure Increase in number of examinations No (inadequate) collimation Image quality is not compatible with imaging task KH Ng Inappropriate exposure • With digital systems, an overexposure can occur without an adverse impact on image quality. • Overexposure may not be recognised by the radiologist or radiographer. In conventional radiography, excessive exposure produces a “black” film and inadequate exposure produces a “white” film, both with reduced contrast. In digital systems, image brightness can be adjusted post processing independent of exposure level. KH Ng Increase in number of examinations In several U.S. hospitals the number of examinations per in-patient day increased by 82% after a transition to film-less operation. Outpatient utilization (i.e. the number of examinations per visit) increased by 21% compared with a net decrease of 19% nationally at film-based hospitals. Reiner et al. Radiology. 2000 ;215(1):163-7 KH Ng No collimation Post-exam collimation (cropping) KH Ng No collimation Apparently “Perfect” radiographs of the paranasal sinuses with post exam cropping Courtesy Dr. Evelyn Ho, SDMC KH Ng No collimation A series of radiographs which were supposed to be for the paranasal sinuses (yellow collimation lines) but instead practically the whole head was x-rayed! Courtesy Dr. Evelyn Ho, SDMC KH Ng No collimation What happens to collimation? Lumbar spine radiography - poor collimation practices after implementation of digital technology Zetterberg and Espeland Brit J Radiol, 84 (2011), 566–569 KH Ng No collimation Lumbar spine radiography - poor collimation practices after implementation of digital technology Irradiated field outside ROI Total field size Digital Analog (Film) 61.7% 42.4% 791 cm2 541 cm2 Zetterberg and Espeland Brit J Radiol, 84 (2011), 566–569 KH Ng No collimation A survey of 450 technologists by the American Society of Radiologic Technologists (ASRT) revealed that half of the respondents used electronic cropping after the exposure Pediatric Radiology, 2011, 41:5, 602-610 KH Ng No collimation • Poor collimation • Large part of the IAEA Radiation Protection in Paediatric Radiology body is irradiated • Not seen on digitally cropped image L04. Radiation protection in digital radiography 30 4. Strategies in monitoring dose KH Ng Nationwide Evaluation of X-ray Trends- NEXT FDA/ CDRH KH Ng National dose monitoring - UK NRPB (HPA) mid 80s IAEA-TECDOC-1423. Optimization of the radiological protection of patients undergoing radiography, fluoroscopy and computed tomography. One of the first online patient dose monitoring systems (QCONLINE) was developed for CR auditing Vano E, et al. Real-time measurement and audit of radiation dose to patients undergoing computed radiography. Radiology 2002; 225(1):283-8. Vano et al Experience on patient dosimetry and quality control on line for diagnostic Fig. 1 and interventional radiology using DICOM services AJR Oct 2012 Vano et al Experience on patient dosimetry and quality control on line for diagnostic and Fig. 2 interventional radiology using DICOM services AJR Oct 2012 Fig. 3 DICOM HEADER Relevant DICOM tags GE Chest flat panel (0008,0020) : Study Date : 27/01/03 (0008,0030) : Study Time : 10:31:12 (0008,0033) : Image Time : 10:32:43 (0010,0020) : Patient ID : 795607 (0010,0040) : Patient's Sex :F (0010,1010) : Patient's Age : 085Y (0018,0015) : Body Part Examined : (0018,0060) : KVP : 125 (0018,1150) : Exposure Time :5 (0018,1151) : X-ray Tube Current : 250 (0018,115E) : Image Area Dose Product : 0.83557 (0018,1190) : Focal Spot(s) : 0.6 (0018,1405) : Relative X-ray Exposure : 61 (0018,7060) : Exposure Control Mode : AUTOMATIC (0018,7062) : Exposure Control Mode Descript: AEC_left_and_right_cells (0028,0010) : Rows (0028,0011) : Columns (0028,0100) : Bits Allocated (0028,0101) : Bits Stored Vano et al AJR Oct 2012 : 2022 : 2022 : 16 : 14 42 Vano et al AJR Oct 2012 Fig. 4 Vano et al AJR Oct 2012 Fig. 5 Vano et al AJR Oct 2012 Fig. 6 Fig. 7 Vano et al AJR Oct 2012 Automated data collection and evaluation for longitudinal assessment of dose. (a) AP lumbar spine radiographs. Even small alterations of the automated exposure control are indicated (arrow). (b) Automated assessment of the kerma-area-product in PA chest radiographs. The majority of exposures are below the DRL level (red line) (Courtesy of Ulrich Neitzel, Philips Medical Systems, Hamburg). Uffmann et al E J Radiol 72 (2009) 202–208 KH Ng “I can assure you our x-ray procedures follow very strict health and safety guidelines” www.CartoonStock.com KH Ng 5. Strategies in Dose Management KH Ng While digital techniques have the potential to reduce patient doses, they also have the potential to significantly increase them. Thus we need to manage dose. KH Ng Optimization Trade-offs between radiation dose and image quality Dose Image quality KH Ng Optimization Optimization does not mean simply maximizing image quality and minimizing patient dose, rather it requires radiologists to determine the level of image quality that is necessary to make the clinical diagnosis and then for the dose to be minimized without compromising this image quality. KH Ng Different medical imaging tasks require different levels of image quality. The objective is to avoid unnecessary patient doses; doses which have no additional benefit for the clinical purpose intended. Diagnostic Reference Levels (DRL) • Useful diagnostic and investigational tool • Acceptable doses for various exams & procedures • Comparison between various facilities • Local DRLs should be set up and reviewed when new digital systems are introduced. KH Ng Examples of diagnostic reference levels (DRL) US 1999 ESAK [mGy] UK 2000 ESD Germany 2003 [mGy] ESD [mGy] AP/PA skull - 3 5 Lat skull - 1.5 3 PA 0.25 0.2 0.3 Lat chest - 1.0 1.5 AP abdomen 4.5 6 10 AP pelvis - 4 10 AP C-spine 1.25 - - AP L-spine 5 6 10 Lat L-spine - 14 30 Uffmann et al E J Radiol 72 (2009) 202–208 KH Ng We need to refine DRL: • For digital radiography • Specific for clinical image quality • Adjust for body weight/ size KH Ng “ … finding the appropriate level of image quality is the most important objective. Keeping the dose low should always be secondary.” - Martin CJ: 20 years of patient dose studies: Where should we go from here? Brit J Radiol 2005 KH Ng Based on ICRP 93 KH Ng Based on ICRP 93 KH Ng Fluoroscopy Use correct technique • intermittent fluoro, image freeze hold Time, Distance, Shielding • Duration of exposure (beam on time) • Distance to source (step back) • Use of protective device 10 Pearls are useful in dose management KH Ng KH Ng L R Digital image of lumbar spine. Fluoroscopy system: 10% dose (left); 100% dose (right) (relative values of dose). Courtesy of R. Loose. ICRP 93 KH Ng Commercial Dose Management Software - Dose Alert system KH Ng 64 DoseWatch Demo 12/11/2012 CAREmonitor Page 65 Copyright © Siemens AG 2011 Advantages and challenges of radiographer-performed fluoroscopy In some countries, radiographers are performing fluoroscopy - Role expansion - Relieve workload of busy radiologists - Handling routine cases, eg. barium meals and enema - May lack clinical knowledge and history of patient, thus long screening time & repeat procedure by radiologists KH Ng BJR1998 71:399-405 DAP measurements for over 1000 barium enema performed by radiologists and radiographers were analysed & compared if there is any stats. sig. in radiation dose to the patients, depending on the category of staff performing the examinations. DAP KH Ng Operator group Mean DAP (Gycm2) Radiologists 1994/95 17.8 Radiologists 1996 18.6 Radiographers 1996 22.3 KH Ng Although radiographers are able to produce consistent diagnostic results, there is increase in patient dose due to extra films taken for reporting, which may be difficult to justify. KH Ng WM Thompson et.al. AJR 2006; 187:706–709 No dose information! We need study on digital fluoroscopy KH Ng 5. Summary KH Ng 1. Appropriate training, particularly in the aspects of patient dose management, should be undertaken by radiologists, medical physicists and radiographers before and during the clinical use of digital techniques. KH Ng 2. National and local diagnostic reference levels (DRL) should be reviewed when new digital systems are introduced in a facility. KH Ng 3. All imaging procedures should be audited (evaluated) at least once a year : • Clinical practice • Image quality • Dose assessment KH Ng 4. The original (raw) image data should be made available to the user not only for objective testing in a rigorous quality assurance program but also for other types of independent tests of the performance of digital-imaging systems. KH Ng 5. When a new digital system or new post-processing software is introduced, an optimisation programme and continuing training should be conducted in parallel. KH Ng 6. QC in digital radiology requires new procedures and protocols. Acceptance and constancy tests should include aspects concerning visualization, transmission and archiving of the images. KH Ng 7. As digital images are easier to acquire and to transmit in communication networks, referring physicians should be fully conversant with the justification criteria for requesting medical x-ray imaging procedures. KH Ng 8. Industry should promote tools to inform radiologists, radiographers and medical physicists about the exposure parameters and the resultant patient doses. The exposure parameters and the resultant patient doses should be standardized, displayed and recorded. KH Ng 9. Making use of radiographic and dosimetric data contained in DICOM header for dose management. KH Ng 10. Educate, Educate, Educate Train, Retrain, Train RETRAIN Collimation is urgently needing attention KH Ng Radiation is Good for You Modified from E Hall