Lecture 6Lecture 6

• Review of Units used in Radiation Safety Review of Units used in Radiation Safety and Radiation Biologyand Radiation Biology

• Assessment of Public DoseAssessment of Public Dose• Unauthorized Use/Removal of Radioactive Unauthorized Use/Removal of Radioactive

MaterialsMaterials• MisadministrationsMisadministrations• Record Keeping RequirementsRecord Keeping Requirements• Area Surveys and Leak TestsArea Surveys and Leak Tests

Measure of

Amount ofradioactive material Ionization in air

Absorbed energy per mass

Absorbed dose weighted by type of radiation

Radiation UnitsRadiation Units

*Note: For most types of radiation 1 R 1 rad = 1 rem

Quantity

Activity

Exposure

Absorbed Dose

Dose Equivalent

Unit

curie (Ci)

roentgen (R)

Rad(mRad)

Rem(mRem)

In some cases, SI units have In some cases, SI units have replaced conventional units.replaced conventional units.

Sources of Average Radiation Dose to the U.S. Population

Radon, 20055%

Internal, 3910%

Terrestrial, 288%

Cosmic, 278%

Nuclear Medicine, 144%

Medical x-rays, 3911%

Consumer Products, 103%

Other, 30.8%

Source: BEIR V Report, 1990

Background RadiationBackground Radiation360 millirem per year360 millirem per year

Radiation Exposures at AMHRadiation Exposures at AMH

• The average occupational radiation exposure to all The average occupational radiation exposure to all personnel, who do not handle radioactive material or personnel, who do not handle radioactive material or perform invasive radiology/cardiology procedures, is perform invasive radiology/cardiology procedures, is less than 100 millirem per year.less than 100 millirem per year.

• For radiation workers, the federal and state For radiation workers, the federal and state annualannual radiation exposure limits are set to safe levels radiation exposure limits are set to safe levels (negligible risk of biological effects). The annual (negligible risk of biological effects). The annual whole body radiation exposure limit is 5000 millirem.whole body radiation exposure limit is 5000 millirem.

Radiation ExposureRadiation Exposure

• Roentgens still used.Roentgens still used.

• One Roentgen = 2.58 Coulomb/KG of airOne Roentgen = 2.58 Coulomb/KG of air

• Therefore, Roentgen is measured as Q/mTherefore, Roentgen is measured as Q/m

• Q/m = Charge/MassQ/m = Charge/Mass

• Useful in the range of photon energies used in Useful in the range of photon energies used in radiological sciences.radiological sciences.

Radiation Exposure Continued,Radiation Exposure Continued,

• Devices expressly designed to measure Devices expressly designed to measure exposure are called air ionization chambers.exposure are called air ionization chambers.

Exposure Exposure • Must be able to assess the intensity of radiation in Must be able to assess the intensity of radiation in

an environment.an environment.

• Devices can measure the magnitude of electrical Devices can measure the magnitude of electrical charge produced in a detector.charge produced in a detector.

• Radiation Exposure means the quantity of Radiation Exposure means the quantity of electrical charged produced per unit mass of air in electrical charged produced per unit mass of air in a detectora detector

Exposure Exposure • Mathematical Definition:Mathematical Definition:

• X = Q/mX = Q/m

• where X = Exposurewhere X = Exposure

• Q Q = charge (in Coulombs) = charge (in Coulombs)

• mm = mass of air = mass of air

Units used for Exposure Units used for Exposure

• Roentgen: 2.58 x 10**-4 C/kg.Roentgen: 2.58 x 10**-4 C/kg.

• Still widely used.Still widely used.

• Most survey meters have scales in units of R, and Most survey meters have scales in units of R, and in cpmin cpm

What is a “Dose” of RadiationWhat is a “Dose” of Radiation??

• When radiation’s energy is deposited into our body’s When radiation’s energy is deposited into our body’s tissues, that is tissues, that is a dosea dose of radiation. of radiation.

• The more energy deposited into the body, the higher the The more energy deposited into the body, the higher the dose.dose.

• Rad Rad is a unit of measure foris a unit of measure for radiation dose.radiation dose.

• Small doses expressed inSmall doses expressed in mrem mrem = 1/1000 rem= 1/1000 rem..

• RemRem & & RR (Roentgens) are similar units that are often (Roentgens) are similar units that are often equated to the Rad.equated to the Rad.

Radiation Absorbed Dose (RAD)Radiation Absorbed Dose (RAD)

• Absorbed dose is measured as E/mAbsorbed dose is measured as E/m

• Where E=energy, m = mass of absorber Where E=energy, m = mass of absorber material.material.

• 1 joule = 1.0 x 101 joule = 1.0 x 1077 ergs ergs

• 1 RAD = 100 ergs of energy deposited /gram 1 RAD = 100 ergs of energy deposited /gram of absorbing material.of absorbing material.

• One Rad = 1.0 x 10One Rad = 1.0 x 105 5 ergs/kilogramergs/kilogram..

Radiation Absorbed Dose (Gray)Radiation Absorbed Dose (Gray)

• One Gray = 1 Joule/kgOne Gray = 1 Joule/kg

• 1 joule = 1.0 x 101 joule = 1.0 x 1077 ergs ergs

• And one Rad = 1.0 x 10And one Rad = 1.0 x 105 5 ergs/kilogram.ergs/kilogram.

• Therefore, one Gray = 100 rads.Therefore, one Gray = 100 rads.

• 1 rad = 0.01 Gray1 rad = 0.01 Gray

Absorbed Dose MeasurementsAbsorbed Dose Measurements

• We want to be able to quantify the amount We want to be able to quantify the amount of damage to a unit mass of tissue. of damage to a unit mass of tissue.

• RAD: Radiation Absorbed DoseRAD: Radiation Absorbed Dose

• SI Unit: GraySI Unit: Gray

• 1 Gray = 100 Rads1 Gray = 100 Rads

• 1 Gray = 1 joule/kg of tissue. 1 Gray = 1 joule/kg of tissue.

• 1 rad = 100 ergs/gm.1 rad = 100 ergs/gm.

Dose EquivalentDose Equivalent

• Different biological effects results from the Different biological effects results from the same dose of different types of radiation.same dose of different types of radiation.

• DE = DQNDE = DQN

• Where, D = absorbed dose in Grays or rads, Q Where, D = absorbed dose in Grays or rads, Q = quality factor for the type of radiation, N = = quality factor for the type of radiation, N = product of all other modifying factors that product of all other modifying factors that apply in a given situation.apply in a given situation.

Equivalent to What?Equivalent to What?

The dose of one type of radiation that The dose of one type of radiation that produces the same amount of biological produces the same amount of biological

damage as the dose of a reference damage as the dose of a reference radiation which produces the radiation which produces the

equivalentequivalent amount of damage. amount of damage.

Effective Dose EquivalentEffective Dose Equivalent

• HHEE = = ΣΣwwii x H x Hii

• Where: HWhere: HEE = Effective dose equivalent, = Effective dose equivalent,

• Σ Σ wwii x H x Hi i Means “the sum of” the product of Means “the sum of” the product of

individual dose equivalents and weighting individual dose equivalents and weighting factor for the particular organ. factor for the particular organ.

Effective Dose EquivalentEffective Dose Equivalent

• The effective dose equivalent for the whole-The effective dose equivalent for the whole-body is the sum of dose-equivalents for body is the sum of dose-equivalents for various organs in the body weighted to various organs in the body weighted to account for different sensitivities of the organs account for different sensitivities of the organs to radiation. It includes the dose from radiation to radiation. It includes the dose from radiation sources internal and/or external to the body. sources internal and/or external to the body. The effective dose equivalent is usually The effective dose equivalent is usually expressed in units of millirem (mrem). expressed in units of millirem (mrem).

Q FactorQ Factor

• Dose is influenced by LET: ionization per unit Dose is influenced by LET: ionization per unit path length. path length.

• LET measured as keV/mm or micron.LET measured as keV/mm or micron.• RBE: Relative Biological Effectiveness, RBE: Relative Biological Effectiveness,

determines the dose equivalent. determines the dose equivalent. • RBE defined: The ratio of the absorbed dose RBE defined: The ratio of the absorbed dose

that produces the same damage as the that produces the same damage as the reference dose.reference dose.

Biological EffectivenessBiological Effectiveness

• Not all types of radiation produce the same Not all types of radiation produce the same level of damage. level of damage.

• Higher LET, such as charged particles, will Higher LET, such as charged particles, will produce greater damage along a path produce greater damage along a path length/ amount of energy imparted to tissue.length/ amount of energy imparted to tissue.

• A quality factor (RBE) relative biological A quality factor (RBE) relative biological effectiveness, is applied to measurements to effectiveness, is applied to measurements to account for this.account for this.

Biological EffectivenessBiological Effectiveness

• REM: Roentgen Equivalent Man.REM: Roentgen Equivalent Man.

• REM takes dose measured in rads and REM takes dose measured in rads and multiplies by the QF to obtain the dose multiplies by the QF to obtain the dose equivalent. Equivalent to what?equivalent. Equivalent to what?

• Gamma and beta radiation are assigned 1.Gamma and beta radiation are assigned 1.

• Therefore, alpha, with QF of 20, is Therefore, alpha, with QF of 20, is equivalent to 20 times the damage from the equivalent to 20 times the damage from the same dose of gamma radiation. same dose of gamma radiation.

RBE ExamplesRBE Examples

• If 20 RADs of x-rays produce the same If 20 RADs of x-rays produce the same biological damage as one rad of neutrons, the biological damage as one rad of neutrons, the RBE is 20. The quality Factor for neutrons of RBE is 20. The quality Factor for neutrons of this type is therefore 20.this type is therefore 20.

• QF is really the only modifying factor used in QF is really the only modifying factor used in practice. Therefore N in the above equation practice. Therefore N in the above equation can be set to 1, giving:DE = DxQcan be set to 1, giving:DE = DxQ

Some Other TermsSome Other Terms

• Flux: # of neutrons, photons, etc, passing Flux: # of neutrons, photons, etc, passing through one cmthrough one cm22/instant of time/instant of time

• Fluence: # of neutrons, photons, etc, that Fluence: # of neutrons, photons, etc, that passed through one cmpassed through one cm2 2 over a period of time.over a period of time.

• Cross Section: a probability of interaction, and Cross Section: a probability of interaction, and thus transmutation after target bombardment.thus transmutation after target bombardment.

Image of the WeekImage of the Week

  

  • PET Scan and PET-CT FusionPET Scan and PET-CT Fusion• PET scan, or Positron Emission PET scan, or Positron Emission

Tomography, is a powerful tool for Tomography, is a powerful tool for detecting several types of cancer.  It is detecting several types of cancer.  It is useful for the accurate detection of useful for the accurate detection of cancer spread in patients with an cancer spread in patients with an established diagnosis of cancer, or for established diagnosis of cancer, or for the noninvasive evaluation of nodules the noninvasive evaluation of nodules detected by chest x-ray or CT.  PET detected by chest x-ray or CT.  PET works by having the ability to detect works by having the ability to detect sites of high metabolic activity.  Since sites of high metabolic activity.  Since many cancers have significantly higher many cancers have significantly higher metabolism than normal tissues or metabolism than normal tissues or noncancerous masses, PET allows noncancerous masses, PET allows sensitive detection of even small sensitive detection of even small cancers.  cancers. 

• These images demonstrate the power of These images demonstrate the power of PET-CT Fusion in identifying spread of PET-CT Fusion in identifying spread of tumor, in this case, spread of melanoma tumor, in this case, spread of melanoma to a patient's liver.to a patient's liver.

Image of the WeekImage of the Week

• PET-CT Fusion is a newer PET-CT Fusion is a newer refinement of the refinement of the technique that allows the technique that allows the most accurate correlation most accurate correlation of anatomic information of anatomic information (from the CT) and (from the CT) and metabolic information metabolic information (from the PET scan) and (from the PET scan) and helps to ensure the highest helps to ensure the highest degree of accuracy for the degree of accuracy for the exam.exam.