Radiophamaceuticals in Nuclear Cardiac Imaging - PowerPoint PPT Presentation

Title: Radiophamaceuticals in Nuclear Cardiac Imaging


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Radiophamaceuticals in Nuclear Cardiac Imaging
Vasken Dilsizian, M.D. Professor of Medicine and
Radiology Director of Cardiovascular Nuclear
Medicine and Cardiac Positron Emission
Tomography University of Maryland School of
Medicine
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Radiopharmaceuticals Used in Nuclear Cardiac
Imaging Procedures

• Myocardial perfusion
• SPECT PET
• Thallium-201 Rubidium-82
• Tc-99m Sestamibi N-13 ammonia
• Tc-99m Tetrofosmin
• Cardiac function
• - Tc-99m Pertechnetate
• Myocardial metabolism
• - F-18 Deoxyglucose

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Clinical Application of Nuclear Cardiac Imaging
Procedures in the Pediatric Population

• Congenital Heart Disease
• Diagnosis of Coronary Circulation Anomalies
• Kawasaki Disease
• Hypertrophic Cardiomyopathy
• Monitoring Chemotherapy

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(Components of the Cardiac Sarcomere)
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Administration of Radiopharmaceuticals in the
Pediatric Population

• It is common for the radiopharmaceutical doses to
  be based on
• Body Weight
• Body Surface Area
• Another approach is to administer Relative Dose
  based on radiation exposure. That is, mCi
  administered to a child that gives the same
  absorbed radiation as 1 mCi administered to an
  adult

Reynolds JC, Proceedings of Workshop for
Treatment of Thyroid Cancer in Childhood, NIH 1992
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Goals of Nuclear Imaging in the Pediatric
Population

• Inject the lowest dose possible without
  sacrificing Image Quality or Diagnostic
  Accuracy
• Risk vs Benefits Risk of radiation exposure vs
  benefits of understanding the underlying disease
  process (inherent in all medical decisions)

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Radiation Exposure With Studies Involving
Radiopharmaceuticals

• Radiopharmaceuticals produce nonhomogeneous
  exposure to the whole body. That is, exposure
  dose varies for each organ depending on the
  biokinetics of the radiopharmaceutical.

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Various Concepts Used to Evaluate the Total Risk
of a Procedure

• Total-body or Whole-body dose The total energy
  deposited in the body divided by the mass of the
  body. This approach assumes a uniform whole-body
  exposure to radiation.
• Effective dose (E) or Effective dose equivalent
  (HE) Involves multiplying individual organ
  doses by risk weighing factors and summing the
  individual contributions into a single dose.

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Tissue Weighing factor (wT)

• The values of wT take into account the numbers of
  1) fatal cancers and 2) risk of hereditary
  disease above normal incidence per unit of
  ionizing radiation for each organ system for
  which such effects are known to occur.

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CALCULATION OF EFFECTIVE DOSE
The effective dose is the sum of the weighted
equivalent doses in all the tissues and organs of
the body. It is given by the expression   E
? T (wT x HT) where E the effective whole body
dose   wT the tissue weighting factor for
tissue T   HT the equivalent dose in tissue or
organ T absorbed dose averaged over a tissue or
organ and weighted for the radiation quality.
The radiation quality factor for clinical
radiation (photons, x-rays) is 1 thus, the
equivalent dose is equal to the absorbed organ
dose.
NIH RSC Report Improving Informed Consent for
Research Radiation Studies, 10/17/2001
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Tissue Weighting Factors, wT (ICRP 73, 1996)1
wT
wT
Organ
Organ
Gonads 0.20
Bone Marrow 0.12
Colon 0.12
Lung 0.12
Stomach 0.12
Bladder 0.05
Breast 0.05
Liver 0.05
Esophagus 0.05
Thyroid 0.05
Skin 0.01
Bone Surface 0.01
  Remainder of tissues or organs 0.05
1 The values have been developed from a reference
population of equal numbers of both sexes and a
wide range of ages. In the definition of
effective dose, they apply to workers, to the
whole population, and to either sex.
International Commission on Radiological
Protection (ICRP), publication 73, 1996 NIH RSC
Report Improving Informed Consent for Research
Radiation Studies, 10/17/2001
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Calculation of Effective Dose for 10mCi of FDG in
an Adult Subject
Effective Dose
Effective Dose
Organ
Dose (rem)
WT
Dose (rem)
Organ
WT
Breasts 0.340 0.050 0.017
Esophagus 0.440 0.050 0.022
Stomach 0.470 0.120 0.056
Colon 0.482 0.120 0.058
Heart 2.200 0.025 0.055
Liver 0.580 0.050 0.029
Lungs 0.640 0.120 0.077
Ovaries 0.530 0.200 0.106
R. Marrow 0.470 0.120 0.056
Bone 0.410 0.010 0.004
Skin 0.300 0.010 0.003
Thyroid 0.390 0.050 0.020
Bladder 3.200 0.050 0.160
Remainder 0.689 0.025 0.017
Effective Dose
0.680
1.000
NIH RSC Report Improving Informed Consent for
Research Radiation Studies, 10/17/2001 Dosimetry
Source Coronado, L. (F-18)FDG Internal Rad Dosim
for Research Protocols, NIH, 10/30/91
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Radiation Risk Estimation
The additional fatal cancer risk for a subject
group, participating in a clinical or research
radiation study, can be estimated by the
following expression   (Total effective dose for
the study, in rem) X (fatal cancer risk per
rem for age group)  
NIH RSC Report Improving Informed Consent for
Research Radiation Studies, 10/17/2001
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Nominal Probability Coefficients for Stochastic
Effects Detriment x 10 4 per rem
 
For children, the risks are 2-3 times greater
than for adults, while for individuals over 50
years of age, the risks are 1/5th to 1/10th of
that of younger cohorts.
International Commission on Radiological
Protection (ICRP), publication 60 (p.22)
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Radiation Risk Estimation
  (Total effective dose for the study, in rem)
X (fatal cancer risk per rem for age group)
  As illustrated in the previous effective dose
calculation (FDG scan of 10 mCi), the additional
estimated increase in fatal cancer risk for the
adult subject is as follows   (0.680 rem) (4.0
x 10 -4 per rem) 0.00027 0.027   Note
that the natural incidence of fatal cancer is
25. Therefore, the theoretical total risk of
fatal cancer for the group of adult subjects
participating in this example study is predicted
as 25.027 , or, rounded to 25.03. It is
important to remember that effective dose is a
theoretical quantity no organ or system,
including the total body, actually receives the
calculated dose.
NIH RSC Report Improving Informed Consent for
Research Radiation Studies, 10/17/2001
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Radiation Dose Guideline Established for
Research Subjects at the NIH
Previous Guideline Organ dose of 3 rem -
quarterly Organ dose of 5 rem -
annual Current Guideline Total effective
dose of 5 rem annual Guideline Value for
Pediatric Subjects (lt18 yrs) 1/10th the adult
value, or 0.5 rem per year
NIH RSC Report Improving Informed Consent for
Research Radiation Studies, 10/17/2001