Ramón Sanchez - Jacob Seminario Web organizado por la Red Latinoamericana de Protección Radiológica en Medicina

1. June 8, 2020
Medical Radiation in Children.
Ramon Sanchez-Jacob MD
Children’s National Medical Center
George Washington University
rsanchezja@gwu.edu

2. NO CONFLICTS OF INTEREST
June 8, 2020

3. Objectives
• Learn about potential risks from the use of ionizing
radiation
• Be familiar with radiation measurements
• Be familiar with ways to control risks

4. Introduction
• The number of imaging tests using ionizing
radiation are increasing
• Children are more susceptible to radiation
damage
– Higher radiation sensitivity
– Longer life expectancy

5. SOURCES OF RADIATION
NATURAL SOURCES
MAN-MADE SOURCES
– Medical imaging
– Nuclear power and
occupational
– Consumer and miscellanea

6. What is the most significant manmade source of
ionizing radiation?
– Nuclear power
– Occupational
– Consumer and miscellanea
– Medical imaging

7. What is the largest source of ionizing radiation in
medical imaging?
• Nuclear medicine
• Interventional radiology
• CT
• Diagnostic radiology and fluoroscopy

9. • 1995-2008
• Number of CT scans
– 1995 = 330,000
– 2008 = 1,650,000
• Percentage of visits
associated with CT
– 1995 = 1.2%
– 2008 = 5.9%
Larson DB, et al. Radiology 2011; 259(3): 793-801

10. • overall CT utilization was 20% for head, 5% for the
chest and 9% for the abdomen and pelvis.
• Children with no injuries or minimal injury to the
head were scanned 7% and 46% of the time,
respectively, for the chest 3% and 13% and for the
abdomen 6% and 30%.
• For all body regions and all levels of injury severity,
level 1 stand-alone pediatric centers displayed
significantly lower CT utilization rates than others.
June 8, 2020

11. How can be measured?
Direct ways
– Exposure: coulombs
• radiation incident on a patient
– Absorbed dose: Gy - rad
• Deposition of energy/unit mass in the patient’s body
tissue
• Two problems:
– Different types of radiation differ in their ability to
produce effects
– Different tissues and organs have different probabilities
and severities of harm

12. indirect ways (sirvent )
– Equivalent Dose
• energy deposited in a
specific organ
• Absorbed dose xWF
– Effective dose
• Converting dose to specific
organs to an equivalent
risk to the whole body
dose, as if the whole body
had been exposed

13. • Cancer
• Genetic effects
• Skin injuries
• Cataracts
• Infertility
• Cell death
• All of the above
What can ionizing radiation do?

14. What is the mechanism of effect of radiation?
• X rays ( photons) deposit energy at nuclear level causing
ionizations
• Ionization damage DNA
– Directly
– Through generation of free radicals
• Effects:
– Immediate: cell death (radiation necrosis)
– Cell damage: (birth defects – cancer)

15. – Effects are dose dependent (the higher the dose, the
greater the effect)
– Depends on the tissue, clinical effect and dose rate
– There is a threshold dose
– Skin effects, cataracts, sterility, decreased
lymphocyte count
– Rare in diagnostic radiology (<0.01%)
DETERMINISTIC EFFECTS

16. Threshold for deterministic effects in adults ( ICRP 103)
Tissue and effect
Threshold
Total dose in a single
exposure
(Gy)
Annual dose if the case of
fractionated exposure
(Gy/y)
Testes
Temporal sterility
Permanent sterility
0.15
3.5-6.0
0.4
2.0
Ovaries
Sterility 2.5-6.0 >0.2
Lens
Detectable opacity
Cataract
0.5-2.0
5.0
>0.1
>0.15
Bone marrow
Depression of
hematopoesis
0.5 >0.4

17. Titus R. Koenig et als. Radiation injury secondary
to cardiac interventional procedure. AJR
2001;177:3–11
CT brain perfusion scan
From the New York Times
Published: July 31, 2010
DO DETERMINISTIC EFFECTS OCCUR ?

18. • Severity of the result is the same but probability of
occurrence increases with dose
• Not threshold dose below which there is no risk
• Occur at lower levels of exposure (diagnostic radiology)
• Examples:
– Cancer ( damage to DNA)
– Hereditary effects ( germ cell)
• The probability of this effect is very low
STOCHASTIC

19. Probability?
• The risks of developing cancer is approx. 10 %/ Sv ( risk
of dying from cancer is 5%/ Sv)
• A single abdominal CT exposes a teenaged patient to
10 msV (approx.)
• Overall lifetime risk of cancer death: 20-25%
• Estimated increased risk of cancer over a lifetime from
a single CT is 0.03-0.05%
• Equal to the risk for a crash if a car is driven 7500 miles
or a motorcycle 1000 miles

20. How can probability of cancer be determined?
• LNT ( linear non threshold model)
– Assumes that damage is proportional to dose at all dose levels ( no
safety threshold)
• Controversial
– True low dose experiments at cellular level are difficult and
still a work in progress

21. How can probability of cancer be determined?
• Based upon epidemiological data:
• Atomic bomb survivors
• Population exposed for medical reasons
• Nuclear workers
• Chernobyl fallout

22. How much radiation is used in paediatric radiology
examinations compared to other exposures?
Estimated dose
Natural background 3 mSv/year
Airline passenger 0.04 mSv
Chest X-ray 0.01 mSv
UGI 1.2-6.5 mSv
VCUG 0.5- 3.2 mSv
Abdominal CT 6-10 mSv
www.imagegently.org
Days of background
radiation
4 days
1 day
8 months
12 months
20 months

23. 23
Radiation risk in paediatric radiology
Examination Lifetime risk of fatal cancer
Limbs 1/a few million
Chest (PA) 1/million
Spine (AP, PA, Lat) 1/150000
Pelvis 1/120000
AXR 1/100000
VCUG 1/10000
CT Head 1/5000
CT Body 1/1000
Cook JV, Imaging, 13 (2001), Number 4
This does not mean that any one child will get cancer from a single X-ray.
It applies to populations of patients.

24. Hereditary effects
• Observed in offspring born after one or both parents
had been irradiated prior to conception
• Estimation is based on:
– animal studies
– Study on descendants of Hiroshima and Nagasaki
survivors did not show statistically significant increase in
abnormalities

25. Way to control risks?
• Follow the principles of radiation protection
– Prevention of tissue reactions (deterministic effect)
– Limiting the probability of stochastic effects

26. Principles of Radiation protection
– Justification
• Process in which the referring provider and radiologist
make a decision as to whether:
– the examination is clinically indicated
– the benefits outweigh the radiation risks
– Optimization
• ALARA (as low as reasonable achievable) principle
without compromising diagnostic image quality

27. Tools to help improve justification
– Considered alternative techniques such as ultrasound and
MRI will be used
– Pay attention to prior exams and information available from
the referring physician , patient and family
– Keep informed about appropriateness criteria and referral
guidelines

28. Examinations should be performed when appropriate and
necessary
• Many unnecessary exams are performed
– Easy and fast
– Almost immediate results
– Overcautious because of potential malpractice
litigation
– Pressure to use high-end technical examinations
– Financial incentive

29. Avoid inappropriate exams by asking yourself:
• Has it been done?
• Do I need it?
• Do I need it now?
• Have I explained the clinical problem?
• Can the information be obtained with different imaging modalities?

30. Optimisation
• All personnel involved with medical radiation exposure should
have received education and training
• Equipment shall be in accordance with international standards
• Tailor examination parameters to size of the child
• Image only indicated area
• Avoid repeated examinations and multiple phase scans

31. Adequate settings
40mA 80mA 250mA
Karmazyn et al. CT with a Computer-Simulated Dose Reduction Technique for Detection of Pediatric
Nephroureterolithiasis: Comparison of Standard and Reduced Radiation Doses. AJR 2009; 192:143–149

32. Avoid multiple acquisitions
Multiphase CT can increase the dose by as much as 2-3
folds over single phase CT

33. Restrict scan length to what is necessary
Shorter scan length: 20-30% dose reduction

34. June 8, 2020

35. How to handle stressed parents
• Inform and discuss with patient benefits and risk
• How medical imaging helps
– It helps diagnosing disease and injury
– It may reduce surgical intervention
– It may shorten hospital stay

36. How to handle stressed parents
• Different radiological exams have different effective
doses
• Individual risks are difficult to estimate
– It is difficult to extrapolate medical radiation risk from back
ground sources and overall cancer risk

37. 37
Summary
1. Children are more radiosensitive, have longer life expectancy
and higher probability of developing cancer
2. Cancer risk at lower doses is low and the exact relationship
remains controversial
3. Effects may take many years to appear
4. Individual risks are difficult to estimate

38. 5. Order and perform examination only when medical benefit is high
6. AAA (Awareness, Appropriateness, Audit) facilitate and enhance
justification
7. Medical imaging is good , necessary and if done correctly, benefits
outweigh risks
8. CT contributes to most of the radiation exposure but remains an
optimal investigation
9.Tailor examination parameters to size of the child
10. Consider use of alternative modalities (US, MRI)

39. seful websites.
• X-Rays: How Safe AreThey.
http://www.hpa.org.uk/webc/HPAwebFile/HPAweb_C/1194947388410
• Referral guidelines.
http://ec.europa.eu/energy/nuclear/radioprotection/publication/doc/118_en.pdf.
• American Academy of Pediatrics
http://aap.org/sections/Radiology/RadiologyPediatricianPage.pdf.
• Image gently campaign. http://www.pedrad.org/associations/5364/ig/
– What Parents Should Know about CT Scans for Children
• http://www.pedrad.org/associations/5364/files/Image_Gently_8.5x11_Brochure2p
g.pdf
– What Parents should know about Medical Radiation Safety
• http://www.pedrad.org/associations/5364/files/Image_Gently_8.5x11_Brochure.pd
f
– What Parents should know about Medical Radiation Safety in Pediatric Interventional
Radiology
• http://www.pedrad.org/associations/5364/files/Im_Gently_8pg_Eng_IR.pdf