How to reduce dose in Pediatric CT imaging By C. Leidecker and T. Flohr www.siemens.com/healthcare DoseReduction_Pediatric.indd 1 07.03.11 17:10 2 DoseReduction_Pediatric.indd 2 07.03.11 17:10 General Anatomical and physiological differences between children and adults require special attention when imaging pediatric patients. Image quality requirements are different because of smaller structures as well as higher heart rates and difficulties in cooperating during the scan, to name a few. Adjusting imaging parameters is important to meet image quality requirements and, in addition, is essential to reduce dose as children are more sensitive to radiation than adults. The most important steps in reducing dose for pediatric patients are: • to be sure that a CT scan is the most appropriate diagnostic test for the clinical question at hand • to scan only the regions that are indicated • to optimize scan parameters to the diagnostic task The dose for each individual scan should be carefully adjusted to achieve the necessary image quality. Scans with lower radiation dose may have higher image noise, but still deliver diagnostic image quality. 3 DoseReduction_Pediatric.indd 3 07.03.11 17:10 Scan preparation Warm surroundings and dimmed lighting are helpful to make children more cooperative. Patient sedation should be considered to avoid rescans due to patient motion. Use fast rotation times and high pitches when possible. Proper patient centering is always important to dose and image quality. Double check and verify the patient’s position with the laser beams as well as in the topogram. If patients are not centered, dose can increase substantially or image quality may be impaired. The use of breast shields is not recommended. If you nevertheless decide to use shielding with your Siemens scanner, it is important to ensure that shields are removed during topogram acquisition. Otherwise the system will increase the dose according to the additional attenuation in the scan area and the potentially positive effect is negated. Always follow the shield manufacturers’ instructions for proper use and placement. 4 DoseReduction_Pediatric.indd 4 07.03.11 17:10 5 DoseReduction_Pediatric.indd 5 07.03.11 17:10 Selecting protocols Use Siemens’ default child protocols As a starting point, Siemens provides default scan protocols for children, tailored to various body regions and procedures. You may customize and save these protocols according to your imaging needs. Please ensure that your protocols are changed only by authorized personnel. Always use a child protocol when imaging pediatric patients. As a guideline, we recommend using pediatric protocols up to a weight of 55 kg (body imaging) or 6 years (head imaging). For body imaging children heavier than 55 kg should be scanned with an adult protocol, for head imaging children older than age 6 should be scanned with an adult protocol. Use Siemens’ CARE Dose4D Child default protocols use CARE Dose4D, Siemens’ automated real-time tube current modulation. Once the reference setting is defined, CARE Dose4D automatically adjusts the tube current to the patient size and anatomy to achieve the diagnostic image quality at lowest possible dose. Once the reference for a protocol is set, do not change this value. If you are using software version syngo CT 2010 or earlier, set the reference value to the one you would choose for a 20 kg patient (see example below). Once the reference is set, do not change this value. CARE Dose4D adjusts the value to the individual patient. If you are using syngo CT 2011 or later, set the reference to the value you would choose for an adult. Do not change the reference value once it has been set for a protocol. For further details on using CARE Dose4D with syngo CT 2011, please refer to the Operator Manual. 6 DoseReduction_Pediatric.indd 6 07.03.11 17:10 Example for Quality ref. mAs settings with CARE Dose4D (SOMATOM Definition AS, syngo CT 2010) Protocol Adult Head Routine Thorax Routine Abdomen Routine 350 eff. mAs 110 eff. mAs 210 eff. mAs Typically reduce to 57% of original value Typically reduce to 45% of original value Typically reduce to 43% of original value 50 eff. mAs 90 eff. mAs Child (Default: 200 eff. mAs CARE Dose4D active) The examples above use a default setting of 120 kV. If you choose to change the kV-value, please adjust mAs-values as well, as described on the next page. 7 DoseReduction_Pediatric.indd 7 07.03.11 17:10 How to reduce dose Avoid multiphase exams Reduce the number of phases when appropriate. Campaigns such as Image Gently (www.imagegently.org) urge clinicians to use single phase scans whenever possible. Use automatic exposure control Always use CARE Dose4D. It adjusts the exposure to the size and attenuation of the individual patient. Using an automatic adjustment maintains uniform image quality for every patient while ensuring that the minimum dose has been used. Use low-kV scanning for contrast enhanced scans For vascular exams, dose savings are possible by lowering the kV-values. Choosing lower kV-settings requires an increase in mAs to maintain image quality. However, even with such increased settings, the dose can be reduced. Low kV-settings for vascular exams When changing kV-values from 120 kV to 100 kV from 120 kV to 80 kV Increase eff. mAs-value by a factor of 1.1 a factor of 1.5 Dose reduction to 65% of value at 120 kV to 50% of value at 120 kV Example: If you have been using 50 eff. mAs at 120 kV for your CTA protocols, use 55 eff. mAs at 100 kV. Example: If you have been using 50 eff. mAs at 120 kV for your CTA protocols, use 75 eff. mAs at 80 kV. 8 DoseReduction_Pediatric.indd 8 07.03.11 17:10 Low kV-settings for other contrast enhanced exams, e.g. liver When changing kV-values from 120 kV to 100 kV from 120 kV to 80 kV Increase eff. mAs-value by a factor of 1.2 a factor of 2.0 Dose reduction to 75% of value at 120 kV to 65% of value at 120 kV 80 kV can be also used for applications when the lowest achievable mAs-value at 120 kV is still too high. When adjusting your mAs-value at the lower kV-setting, monitor the CTDIvol until the desired value is reached. Use lower dose where low contrast resolution is not required Examples for scans that may not need optimal low contrast resolution include lung and bone imaging as well as follow-up studies for shunt or tube placement. Use organ based dose modulation If radiation sensitive organs are exposed during the scan, e.g. breast tissue in thoracic exams, use X-CARE if available on your system. X-CARE provides organ specific dose savings without the disadvantages of in-plane shielding. Use the appropriate reconstruction technique Avoid sub-millimeter slices. Thicker slices, selection of a smoother kernel and wider windowing reduce image noise, and, in return, help reduce dose if scan parameters are changed for future exams. Use advanced reconstruction techniques like Iterative Reconstruction, when available. Thus, a dose reduction of up to 60% can be achieved. 9 DoseReduction_Pediatric.indd 9 07.03.11 17:10 Dose reporting Siemens provides all the necessary tools for efficient dose management and monitoring. Dose is reported in terms of CTDIvol and DLP, as required by IEC standards. This represents the dose delivered to a reference phantom reported in a standard way for all scanners and does not reflect actual exposure to any given patient. For all Siemens‘ protocols including pediatrics, as defined by the IEC, the CTDIvol is measured in the 32 cm phantom for all body exams and in the 16 cm phantom for all head exams. The CTDIvol is displayed prior to the exam and reflects changes in scan parameters. Both CTDIvol and DLP are available after each individual exam through either the Patient Protocol page or the Dose Structured Report (Dose SR). The Patient Protocol and Dose SR are automatically saved as separate series at the end of the exam, and are available for viewing and archiving as a series in the Patient Exam. National organizations such as BfS and ACR provide recommendations on reference dose levels in terms of CTDIvol and DLP. We recommend including dose information in terms of CTDIvol and DLP in each patient report for future reference and potential optimization of protocols. Radiation risk associated with CT imaging is poorly understood. The easiest way to reduce risk is by reducing patient dose according to the ALARA principle (As Low As Reasonably Achievable) when optimizing pediatric protocols. IEC: International Electrotechnical Commission BfS: Bundesamt für Strahlenschutz, Federal Office for Radiation Protection, Germany ACR: American College of Radiology, USA 10 DoseReduction_Pediatric.indd 10 07.03.11 17:10 11 DoseReduction_Pediatric.indd 11 07.03.11 17:10 In the event that upgrades require FDA approval, Note: Any technical data contained in Siemens cannot predict whether or when the FDA this document may vary within will issue its approval. Therefore, if regulatory defined tolerances. Original images clearance is obtained and is applicable to this always lose a certain amount package, it will be made available according to of detail when reproduced. the terms of this offer. Please find fitting accessories: On account of certain regional limitations of www.siemens.com/medical- sales rights and service availability, we cannot accessories guarantee that all products included in this brochure are available through the Siemens sales organization worldwide. Availability and packaging may vary by country and are subject Global Business Unit to change without prior notice. Some/All of the features and products described herein may not be available in the United States. The information in this document contains general technical descriptions of specifications and options as well as standard and optional features which do not always have to be present Siemens AG Medical Solutions Computed Tomography Siemensstr. 1 DE-91301 Forchheim Germany Phone: +49 9191 18 0 Fax: +49 9191 18 9998 in individual cases. Siemens reserves the right to modify the design, packaging, specifications, and options described herein without prior notice. Please contact your local Siemens sales representative for the most current information. Siemens Global Headquarters Siemens AG Wittelsbacherplatz 2 80333 Muenchen Germany Legal Manufacturer Siemens AG Wittelsbacherplatz 2 DE-80333 Muenchen Germany Siemens Healthcare Global Headquarters Siemens AG Healthcare Sector Henkestr. 127 91052 Erlangen Germany Phone: +49 9131 84-0 www.siemens.com/healthcare www.siemens.com/healthcare Order No. A91CT-23013-11C1-7600 | Printed in Germany | 03.2011, Siemens AG DoseReduction_Pediatric.indd 12 07.03.11 17:10 Glossary seReduction_Glossary.indd 1 Observe patient reaction carefully, because it is important for your scan. Have a careful look at the ECG now – it may help you in deciding the next step. Be careful! Your contrast protocol might be influenced. By taking these points into consideration you can significantly reduce dose. Action required by user. Something needs to be changed in the scan protocol. This is a technical fact with some extra explanation here. This is a special tip for solving a difficult problem. Carefully assure an optimized patient positioning. 07.03.11 17:1 seReduction_Glossary.indd 2 How to reduce dose? 07.03.11 17:1