Pediatric Dose in CT Imaging

Pediatric Dose in CT Imaging By the end of this course, you will be able to: Explain the relevance of pediatric CT imaging in the 21st century. Describe low-dose radiation risk as it pertains to patients undergoing CT examinations List the biological effects of ionizing radiation Identify barriers of reducing patient's dose in CT, especially for children Explain measures to protect children from unnecessary CT procedures and methods CT as invaluable diagnostic tool Technological advancements Public perception and awareness Scientific literature USA 2nd after Japan (1) 7 million CT exams/year (2) 10% annual increase (3) 33% under age of 10 (4) (1) American Academy of Pediatrics. (2016). What every pediatrician should know. Retrieved from https://www.aap.org/en-us/about-the-aap/Committees-Councils-Sections/Section-on-Radiology/Pages/What-Every-Pediatrician-Should-Know.aspx (2) Shah, N. B., & Platt, S. L. (2008). ALARA: is there a cause for alarm? Reducing radiation risks from computed tomography scanning in children. Current Opinion in Pediatrics, 20(3), 243-247. doi:10.1097/mop.0b013e3282ffafd2 (3) Nellist, C. C. (2012, June 12). As CT scans increase, concern of radiation risk rises. Retrieved from http://www.oncologypractice.com/specialty-focus/head-neck/single-article-page/as-ct-scans-increase-concern-of-radiation-risk-rises/4804e87d04e5ea49855c003c3516f2ef.html (4) Image Gently. (n.d.). Frequently asked questions - Medical professionals. Retrieved from http://www.imagegently.org/Portals/6/FAQs-Medical%20Professionals.pdf Is there an increased risk of cancer from CT examination? Theory or proven fact? Atomic Bomb Survivors Radiation induced cancer Current radiation risk estimates based on linear no threshold model All radiation doses, even those close to zero, are harmful. Low doses are held to have the same effects as high doses, but with lower incidence. Children have  more radiosensitive tissue Cells unable to repair mutations Longer time for cancer development Cells have more time to manifest mutation effects Risk small but cumulative for individual Risk larger to entire children population due to increased CT exams performed Risk not zero Children’s tissues up to 10 times more radiosensitive Children have a longer life expectancy , which means a greater chance for expressing radiation damage The Risk Is Not Zero Increased dose Dark image when overexposed in conventional X-ray Not so in CT Overexposed CT images do not show compromised image quality No “too light or too dark” image More is not better The more dose the smoother images Noise in images is bad Adult exposure parameters result in larger doses for children “Down-size” for children Reducing exposure parameters significantly while maintaining diagnostic image quality UFC™  Detector Ultra Fast Ceramic Stellar Detector Integrated electronic components Reduces electronic noise Efficient filtration of the x-ray beam to reduce exposure from low energy radiation Polychromatic X-ray beam Energy dependent attenuation Low energy levels Not used for image Only Increase dose Appropriate filtration to Reduce unwanted low energy photons Harden the X-ray beam Bow tie filters for a uniform dose distribution X-ray Beam collimation to reduce dose Affects patient dose and image quality Pre and post patient collimation Appropriate beam width and geometry Reduce in scatter Automatic Exposure Control (AEC)=CARE Dose 4D Fully automated dose management system Every patient is unique Anatomy based No user interaction How does it work? One topogram only Evaluation of cross-sectional anatomy in real-time Online tube current adjustment according to anatomy of each individual organ during spiral scan  Fully automated dose management for adults and children with up to 68% dose reduction** **CARE Dose4D combines angular and z-axis tube current modulation to a fully automated exposure control. Studies on clinical patients (Radiology 2005 (237): 213–223; AJR 2006 (186): 673–679; AJR 2006 (187): 695-701; AJR 2008 (190): 1232–1240; Acta Radiol 2010 (6): 625-634; Radiation Protection Dosimetry 2010 (139): 173–179; Acta Radiol 2011: 1–6; Acad Radiol, 2011 (18): 690-693) suggest that based on the total DLP dose savings of up to 68% may be achieved (compared to CT scans with no tube current modulation). Clinical results may vary depending on the setup of the selected scan protocol, the body region under consideration as well as age and physique of the patient; the maximum value of 68% dose reduction in the referenced clinical studies was achieved in a cervical spine examination. The systems allows for estimating the actual dose savings for a given patient prior to the scan. Select proper pediatric protocols Technique charts based on weight, diameter, age Two to four fold dose reduction Defines the desired image quality - or noise value - for a protocol for an averaged sized patient Average sized patient = 70 - 80kg Adjust exposure parameter (kV) to patient size kV – Optimizes contrast to noise ratio 70 - 80kV Neonates & newborns CTA’s & airway exams 100kV Small children CTA’s & airway exams 120kV Adolescents Head exams Reduced rotation time Fast rotation times typically used for cardiac CTA Useful to reduce motion in pediatric scanning Like rotation time, faster pitch values will Increase scan speed Maintain dose On older CT systems it was possible to acquire thicker slices to increase scan speed lower dose Adaptive Dose Shield – helps protect against clinically irrelevant dose Available on newer Siemens CT scanners Reduces dose by eliminating “over scanning” radiation at beginning and end of scan Why unnecessary radiation exposure? Single –slice CT scanners – half-slice width “over scanning” Multi-slice CT scanners – more “over scanning” as detector size grows How does adaptive dose shield work? Collimators physically block x-ray beam Blocked beam unable to reach tissue outside ROI Minimizes over-radiation pre- and post-spiral Patient Shielding Radiosensitive organs Breast, eye lenses, gonads Out-of-scan-field shielding Lead apron - 360° shielding Dose from incidental radiation is reduced Patient reassurance In-plane shielding Shielding of tissue in scanned region Bismuth impregnated synthetic rubber material for eyes, thyroid, breast in different sizes Image artifacts Streaking Blooming Increased noise Physicians CT technologists CT manufacturers Medical and governmental organizations ALARA—as low as reasonably achievable X-rays: interact with body tissue scattered and/or absorbed deposit their energy in tissue energy deposit is called “dose” Ion dose measured in Roentgen (R) 1 R = 2.58 x 10-4 C/kg 1 R = 1000 mR Absorbed dose measured in Gray (Gy) 1 Gy = 1 J/kg 1 Gy = 1000 mGy Conversion Roentgen > Gray 1R=8.7 mGy CT Dose Index (CTDI) Measured in plastic phantoms with diameters similar to the human body 16 cm for head 32 cm for body Measured with ionization chambers in five positions different definitions of CTDI CTDIFDA American Association of Physicists in Medicine. (2008). The measurement, reporting, and management of radiation dose in CT (96). Retrieved from AAPM website: https://www.aapm.org/pubs/reports/RPT_96.pdf   CTDI100 100 as an international standard Most dose chambers have length of 100 mm Dose always integrated over Not clinically relevant Dose measured in center is always lower than at surface Dose not uniformly distributed Introduction of mean dose estimate as CTDIw   CTDIw = 1/3 CTDI100 center+ 2/3 CDTI100 edge Useful when comparing scan procedures and scanner types CTDIvol = 1 / pitch x CTDIw Table speed/collimation (pitch) reflected in CTDIvol Introduced in 2003 by International Electrotechnical Commission  Average absorbed dose over x, y, and z axis Displayed on your Siemens CT scanner (Examination Task Card) CTDI air or dose in isocenter Measured without phantom  Used for technical checks on your scanner Dose Length Product (DLP) Measured in mGy cm DLP (mGy cm) = CTDIvol (mGy) x L (scan length (cm)) DLP increases with increased scan distance covered DLP product of two independent factors DLP depended on CT parameters Similar to CTDI, DLP does not reflect dose to individual patient Where is the information displayed? UI (User Interface – Examination/Routine and Scan Tab Card) CTDIvol is an estimate without dose modulation prior to scan Protocol page CTDIvol averaged over total scan volume DLP reflects scan length What does effective dose mean? Includes not only primarily irradiated organs Whole body, all organs Measured in mSv Biological sensitivity Estimation Calculation of effective dose per DLP E (mSv) ~ k x DLP Effective dose conversion coefficient Is the facility and staff committed to the principles of ALARA? Are dose reduction strategies consistently employed? Is the facility accredited by the ACR – the American College of Radiology? Are the technologists certified by the A.R.R.T. – American Registry of Radiologic Technologists? Are the radiologists board certified radiologists or pediatric radiologists? CT equipment regulated by FDA as radiation-emitting devices and as medical devices Other organizations – ACR, AAPM – set acceptable use standards for dose reduction MITA Smart Initiative - XR-29 Measures to protect children from unnecessary exposure during CT procedures Eliminate inappropriate referrals for CT Reduce the number of multiple scans with contrast material Scan only the indicated area Scan only the smallest necessary area Eliminate needless exposure   House bill encourages providers to use lowest possible radiation dose with children Society of Pediatric Radiology Alliance for Radiation Safety in Pediatric Imaging Imager Gently campaign How much dose will my child receive from this scan? Other <1% Consumer Products 3% Nuclear Medicine 4% Medical X-rays 11% Internal 11% Terrestrial 8% Cosmic 8% Radon 54% Sources of Radiation Exposure to the US Population University of Washington. (2014, February 14).  Sources of radiation exposure to the US population [Graph].  Retrieved from https://www.ehs.washington.edu/rsotrain/rad_bioeffects/page46.shtm Relative Doses From Radiation Sources Millirem Doses Radon in average home 200 millirem (annual) Diagnostic radiology 50 millirem (annual) Mammogram 30 millirem (single procedure) Cosmic radioactivity 27 millirem (annual) Chest X-ray 10 millirem (single procedure) Highest recorded WIPP air sample reading 2.4 millirem Gastrointestinal Series 1,400 millirem (single procedure) Cosmic radiation living in Denver 50 millirem (annual) Natural radioactivity in the body 40 millirem (annual) Terrestrial radioactivity 28 millirem (annual) Cosmic radiation living at sea level 24 millirem (annual) Living near a nuclear power station <1 millirem on average (annual) Highest recorded air sample reading outside WIPP Landwithdrawal Area 0.3 millirem U.S. Department of Energy. (n.d.). Relative doses from radiation sources millirem doses [Chart].   Retrieved from http://www.wipp.energy.gov/wipprecovery/images/relative.jpg A - As L - Low A - As R - Reasonably A - Achievable You should now be able to: Explain the relevance of pediatric CT imaging in the 21st century Describe low-dose radiation risk as it pertains to patients undergoing CT examinations List the biological effects of ionizing radiation Identify barriers of reducing patient's dose in CT, especially for children Explain measures to protect children from unnecessary CT procedures and methods