Presentation on theme: "Assessing Risk from Medical Radiation"— Presentation transcript:
1Assessing Risk from Medical Radiation Elizabeth H. Ey, M.D.Medical Director RadiologyDayton Children’s Medical Center
2Content of presentation and pictures courtesy of Thomas Slovis, M. D Content of presentation and pictures courtesy of Thomas Slovis, M.D. and The Society for Pediatric Radiology
3SurveyHas anyone here read a news report of radiation exposure from medical imaging?
4SurveyHas anyone had a patient or family member ask them about radiation exposure from medical imaging?
5SurveyHas anyone had a test question in medical education (or CME) regarding radiation exposure to patients from medical imaging tests?
6Questions What is our natural background level of radiation? What is the radiation dose of a 1 view chest radiograph?What is the radiation dose of a 1 view abdomen radiograph?What is the radiation dose of a CT scan?Head CT dose?Abdomen CT dose?
8What is the increased risk of death from cancer from 1 CT scan performed in a child? A The increased risk of cancer death from a CT scan is 0.B The increased risk of cancer death is between 1 in 1000 to 1 in 5000 over a lifetime.C The increased risk of cancer death is 1 in 1 million over a lifetime.
9AnswerB It is estimated that an abdominal CT scan results in 1/1000 to 1/5000 excess risk of cancer at a later date.
10What is the current lifetime risk of developing cancer (US)?dying of cancer (US)?
11Lifetime risk of cancer (US) Developing Dying Male 44.05% 23.24% Female 37.6% 19.65%
15Medical Radiation in Medicine When indicated it can diagnose illnessNoninvasive, painless, fast, extremely accurateBut like any medication or therapyToo much radiation can lead to deleterious effectsDETERMINISTIC effect –linear, direct, ex: skin reddeningAny radiation dose can cause lethal effect – cancerSTOCHASTIC effect – non-linear, random, takes time to see
16Think of radiation as a medicine Effects are lifelong and cumulativeParticularly severe effect in infants and childrenEspecially when adult doses are used in childrenAge dependent – younger patient more severely effectedNo dose of radiation can be considered completely safeLinear non-threshold effect
18ALARA Concept for Pediatric Radiation Dose AsLowReasonablyAchievable
19Medical Radiation in Children History of RadiologyBasic dosimetryBiology of radiation effectsUnique issues with radiation in childrenUse of appropriate techniquesJoint efforts with healthcare providers
20HistoryDec 28, 1895: Roentgen submits manuscript describing his discovery of “x-ray” to the Physical Medical Society of Wurzburg: manuscript printed and distributed in 3 daysJan 9, 1896: manuscript appears in Vienna PressJan 23, 1896: manuscript appears in Nature, in EnglandJan 23, 1896: Roentgen presented paper to Physical Medical Society of WurzburgBy mid 1896, fluoroscopy was in widespread practiceFrom clinical bench to widespread use in 6 months
21Wurzburg Medical-Physics Society 1896 Dr. Kohler, famous anatomist, having hand X-rayedby Roentgen at the meeting.
31Monument to Martyrs in X-ray and Radium Physics – 1936 Hamburg Albers SchonbergMadame CurieCaldwellCodman
32Br J Radiol 2001; 74: 507- 519 Berrington A, Darby SC, Weiss HA, Doll R Research on 100 years of data on health of radiologists in Great Britain– 41% excess of cancer deaths in practitioners of radiology– zero excess mortality from cancer in the practitioners of radiology
33Learned biologic effects of radiation Applied what we learned to protect ourselvesIt workedBut have we done enough?Have we protected our patients enough?
342. Basic dosimetryDose unitsMeasures of doseConversions
36Methods of Measuring Radiation Dose Widely varied and difficult to compareEntrance skin doseExit doseDose area product (DAP)Organ dose –specific to radiosensitive organRadiation output measured within a phantomCT dose index (CTDI)Dose equivalentEffective dose
37Radiation Dose Measurements Used for Risk Assessment Absorbed Dose – Gray or Gy (previous rad)Risk assessment for a specific organ or tissueDifficult to measure and not very usefulEffective dose equivalent – Sievert or Sv (previous rem)Non-uniform exposure to organ or regionExpression of risk equivalent to whole body exposureCT scanner dose units not usefulCTDI vol and DLP determined by phantomNot helpful for assigning risk without conversionNon
38CTDI – CT Dose Index Reported on scanner consoles Based on phantom (16 or 32 cm diameter)Only represents the dose to the phantom based on CT parameters selectedDoes not indicate dose to the child in the CT scannerConversions of CTDI to effective dose are only rough estimations for childrene.g. no age based chest modifications
45AJR July 2001 - Skin burns from cardiac interventional procedures
46Stochastic Effect Low dose, random effect Non dose dependent: Risk of the effect is dose dependent but the severity of the effect is not.Example: Risk of cancer increases with increasing dose but the severity of the type of cancer is not dose dependentThere is “no threshold” to this effect
47Stochastic Effect Means all or none (random effect) Not based on a particular doseBut with higher radiation absorbed dose,the higher the likelihood of genetic damageMostly concerned with risk of carcinogenesisIncidence – twice the mortality riskMortality - risks that are quoted here
48Biological effects of radiation damage to DNA Reactions are rapidInduction of cancer takes many yearsThe damage to DNA may lead to genomic instability
49Genomic Instability“Persistent enhancement in the rate of which genetic change arises in the descendents …..” Little
50Stochastic Effect (Random) on Irradiated Stem Cells C. and D. are the effects seen in realityThe irradiated cell transmits the genetic defect randomly into future cell generationsCancer may not be seen for several cell generationsLittle JB: Ionizing Radiation in Cancer in Medicine 2003
514. Unique issues with radiation exposure to children Children are smaller and have more radiation sensitive tissueHave a longer life expectancy in which to express the damaging effect of radiationIs there a threshold for low dose radiation in which no effect will be seen? Debated
52Breast Cancer and Scoliosis Films Doody et al. Spine 25: year 2000
53Thyroid Cancer after Childhood Radiotherapy Ron, E Pediatric Radiology :
54Infant Radiotherapy for “Enlarged Thymus” … 96 minutes of x rays
55Fetal Exposure Oxford Study of Childhood Cancer Obituary in New York Times 2002
56Cancer risk in fetuses exposed in 3rd trimester The excessive risk is 47% in the fetuses irradiated.
57Atomic Bomb Survivor Follow Up Pierce and Preston 2000 Original 84,000 survivors followed for 55 yearsEventually had 50,000 survivors that were followed ( )Increased cancer rate even at low dose ( Sv or 500 mrad-1.5 rad)Excessive cancer deaths were demonstrated
58Pierce et al; Rad Res 154 pg 183: 2000 .... = cancer death rate for at-risk population (A bomb survivors)__ = cancer death rate otherwise expectedStraight lines represent two different starting points to guess at which point radiation dose is a problem. One begins at zero and the other at 0.06 Sv.
59Is there a safe dose? Linear non-threshold (NLT) dose Dose below which there is no risk of carcinogenesis?
60NCRP Report – cannot prove safety of any radiation dose
61Linear No-threshold Principle “There is no need to even consider a linear no-threshold principle when we have direct human evidence of carcinogenesis at doses of <10mSv.”Pierce DA, Preston DL 2000; 154:
62Linear No-threshold Principle LNT is NOT the issue!“Other populations” have not had 50 years of meticulous research to detect cancerSample size – 84,000 people at start of studyAge at exposure was known from the startLength of follow-up – over 55 years of f/u
68Brenner et al 2003“Above doses of mSv (protracted exposure) or mSv (acute exposure), direct epidemiologic evidence from human populations demonstrate the exposure to ionizing radiation increases the risk of some cancer.”
70CT Use in the US Increased dramatically in the recent years Estimated that 11% of all CT scans performed in the US are performed in childrenThere is a risk of cancer death from CT radiation doseThe younger the patient, the greater the risk
72Infants are 10-15 times more vulnerable than middle age adults Brenner et al; Pediatric Radiology, Apr 2002: pg 230
73Females are at higher risk Females are at higher risk. Age at exposure is the most important factor.Hall Pediatric Radiology Apr 2002 pg 226
74Important Concepts Greatest effect is on actively growing cells Infant, fetusCumulative dose, life long effectEDE – Effective Dose EquivalentFor the same dose, a child is much more vulnerable because of the way the dose is calculated.When measuring the dose at the midpoint of an adult phantom (32 cm), the beam has already passed completely through the child.
75Consider the Premature Infant HepatoblastomaOccurs at a higher rate in premature infants (40%)Infants studied by Alicia Stewart were term infantsOur premature infants can now survive at weeks gestationThe premature infant is at much higher risk to radiation exposure.
765. Use of Appropriate Technique Film screen radiography - using more radiation exposure than needed results in a black imageDigital and computed radiography with post-processing – can make almost any overexposed image look diagnostic by manipulating contrast and brightness
77Shunt Survey Can’t tell technique just by looking at it
79Dose parameters should be included whenever possible
80Uncoupling end result from information regarding dose is a dangerous practice When the exam does not include the technique parameters used to acquire the images,The amount of radiation used may be more than needed.
81Assessing RiskCT related cancer death /million in a life time (not per year)Radiation dose times less than CT dose
826. Joint Efforts of Health Care Workers What can be done? What resources are available?
83We are all responsible Practitioner who orders CT Radiologist who determines CT protocolCT technologist that performs the CT scan
84How do we respond? Be sure that an imaging test is necessary Use the least invasive modality which gives a high likelihood of correct diagnosisConsider all the options for imagingMR and US use NO radiationDiscuss the case with a pediatric radiologist if uncertain which modality to use
85When CT is used appropriately It saves livesFast, accurate, comprehensiveEspecially useful for trauma patients or emergency conditionsIt has the greatest detail in imagingSub mm resolution (IAC), high resolution lung detailIt is less sensitive to patient motion than MRIt is less sensitive to gas than USIt creates a volume of data which permits multiplanar reconstruction as well as 3D surface rendering
86How do we respond? www.ImageGently.com Understand the radiation doses associated with various imaging modalitiesOrder imaging tests on basis of medical indications, not because of parental/legal/insurance pressureDiscuss problem cases with radiologist, engage their expertiseInform parents/patients of radiation risk
87What is the best (most appropriate) imaging exam What is the best (most appropriate) imaging exam? What are the alternatives?First febrile seizureFirst non-febrile seizureHeadachesRLQ abdominal painAcute flank pain with hematuriaUnusual head shapeEvaluate vascular ring
88Image Gently More is often not better. One size does not fit all... There's no question: CT helps us save kids' lives. But, when we image, radiation matters!Children are more sensitive to radiation.What we do now lasts their lifetimes.So, when we image, let's image gently:More is often not better.
89Image Gently When CT is the right thing to do: Child size the kVp and mA One scan (single phase) is often enoughGet as much information as possible from the single phase (IV contrast, enteric contrast) Scan only the indicated area
90ALARAAs Low As Reasonably AchievableTheir future is in our hands.