Lecture 6 Review of Units used in Radiation Safety and Radiation Biology Assessment of Public Dose Unauthorized Use/Removal of Radioactive Materials Misadministrations Record Keeping Requirements Area Surveys and Leak Tests

Radiation Units *Note: For most types of radiation 1 R  1 rad = 1 rem Measure of Amount of radioactive material Ionization in air Absorbed energy per mass Absorbed dose weighted by type of radiation Quantity Activity Exposure Absorbed Dose Dose Equivalent Unit curie (Ci) roentgen (R) Rad (mRad) Rem (mRem) Radiation Units A curie is a very large amount of radioactivity. Nuclear medicine and Radiation Oncology patients are injected (or administered) µCi to mCi quantities of radioactive material for routine diagnostic exams or therapeutic treatments The basic unit of radiation dose is the rad. The rad is defined as the deposition of 0.01 joule of energy (a small amount) per kilogram (kg) of tissue. A rad of x-rays, a rad of gamma rays, and a rad of beta particles are about equally damaging to tissue. However, a rad of another type of ionizing radiation, such as alpha particles or neutrons, is much more damaging to tissue than a rad of gamma rays. The rem was introduced to take into account this variation in tissue damage. This is important because a person may be exposed to more than one type of radiation. For example, it was found that 100 rad of gamma and beta radiation produced the same effect as 100 rad of x-rays. However, only 20 rad of neutrons and 5 rad of alpha particles produced the same effect as 100 rad of x-rays. Therefore, neutron and alpha radiations were more potent and required fewer rad to produce the same effect. The number of rem is calculated by multiplying the number of rad by a radiation weighting factor that accounts for the relative amount of biological damage produced by a specific type of radiation. The radiation weighting factor for x-rays, gamma rays, and beta particles is 1. Thus, a rad of one of these radiations is equal to one rem. For other types of radiation (that are less likely to be present in accidents), the quality factor may be higher. The International Scientific System (SI) assigns different units to the quantities: 1 R = 2.58 X 10-4 C kg-1 1 gray (Gy) = 100 rad 1 sievert (Sv) = 100 rem 1 becquerel (Bq) = 1 disintegration per second *Note: For most types of radiation 1 R  1 rad = 1 rem

In some cases, SI units have replaced conventional units.

Natural Radioactivity in Your Body Nuclide Activity . Uranium 30 pCi (1.1 Bq) Thorium 3 pCi (0.11 Bq) Potassium 40 120 nCi (4.4 kBq) Radium 30 pCi (1.1 Bq) Carbon 14 0.4 µCi (15 kBq) Tritium 0.6 nCi (23 Bq) Polonium 1 nCi (37 Bq)

Background Radiation 360 millirem per year Source: BEIR V Report, 1990

Radiation Exposures at AMH The average occupational radiation exposure to all personnel, who do not handle radioactive material or perform invasive radiology/cardiology procedures, is less than 100 millirem per year. For radiation workers, the federal and state annual radiation exposure limits are set to safe levels (negligible risk of biological effects). The annual whole body radiation exposure limit is 5000 millirem.

Radiation Exposure Roentgens still used. One Roentgen = 2.58 Coulomb/KG of air Therefore, Roentgen is measured as Q/m Q/m = Charge/Mass Useful in the range of photon energies used in radiological sciences.

Radiation Exposure Continued, Devices expressly designed to measure exposure are called air ionization chambers.

Exposure Must be able to assess the intensity of radiation in an environment. Devices can measure the magnitude of electrical charge produced in a detector. Radiation Exposure means the quantity of electrical charged produced per unit mass of air in a detector

Exposure Mathematical Definition: X = Q/m where X = Exposure Q = charge (in Coulombs) m = mass of air

Units used for Exposure Roentgen: 2.58 x 10**-4 C/kg. Still widely used. Most survey meters have scales in units of R, and in cpm

What is a “Dose” of Radiation? When radiation’s energy is deposited into our body’s tissues, that is a dose of radiation. The more energy deposited into the body, the higher the dose. Rad is a unit of measure for radiation dose. Small doses expressed in mrem = 1/1000 rem. Rem & R (Roentgens) are similar units that are often equated to the Rad. BEGIN: III. Radiation Exposure and Biological Effects Lecture: Read slide Remember, I mentioned earlier that not all types of radiation are equally effective at causing biological damage The important concept from this slide is the UNIT of radiation exposure/dose

Radiation Absorbed Dose (RAD) Absorbed dose is measured as E/m Where E=energy, m = mass of absorber material. 1 joule = 1.0 x 107 ergs 1 RAD = 100 ergs of energy deposited /gram of absorbing material. One Rad = 1.0 x 105 ergs/kilogram.

Radiation Absorbed Dose (Gray) One Gray = 1 Joule/kg 1 joule = 1.0 x 107 ergs And one Rad = 1.0 x 105 ergs/kilogram. Therefore, one Gray = 100 rads. 1 rad = 0.01 Gray

Absorbed Dose Measurements We want to be able to quantify the amount of damage to a unit mass of tissue. RAD: Radiation Absorbed Dose SI Unit: Gray 1 Gray = 100 Rads 1 Gray = 1 joule/kg of tissue. 1 rad = 100 ergs/gm.

Dose Equivalent Different biological effects results from the same dose of different types of radiation. DE = DQN Where, D = absorbed dose in Grays or rads, Q = quality factor for the type of radiation, N = product of all other modifying factors that apply in a given situation.

Equivalent to What? The dose of one type of radiation that produces the same amount of biological damage as the dose of a reference radiation which produces the equivalent amount of damage.

Effective Dose Equivalent HE = Σwi x Hi Where: HE = Effective dose equivalent, Σ wi x Hi Means “the sum of” the product of individual dose equivalents and weighting factor for the particular organ.

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

Q Factor Dose is influenced by LET: ionization per unit path length. LET measured as keV/mm or micron. RBE: Relative Biological Effectiveness, determines the dose equivalent. RBE defined: The ratio of the absorbed dose that produces the same damage as the reference dose.

Biological Effectiveness Not all types of radiation produce the same level of damage. Higher LET, such as charged particles, will produce greater damage along a path length/ amount of energy imparted to tissue. A quality factor (RBE) relative biological effectiveness, is applied to measurements to account for this.

Biological Effectiveness REM: Roentgen Equivalent Man. REM takes dose measured in rads and multiplies by the QF to obtain the dose equivalent. Equivalent to what? Gamma and beta radiation are assigned 1. Therefore, alpha, with QF of 20, is equivalent to 20 times the damage from the same dose of gamma radiation.

RBE Examples If 20 RADs of x-rays produce the same biological damage as one rad of neutrons, the RBE is 20. The quality Factor for neutrons of this type is therefore 20. QF is really the only modifying factor used in practice. Therefore N in the above equation can be set to 1, giving:DE = DxQ

Some Other Terms Flux: # of neutrons, photons, etc, passing through one cm2/instant of time Fluence: # of neutrons, photons, etc, that passed through one cm2 over a period of time. Cross Section: a probability of interaction, and thus transmutation after target bombardment.

Image of the Week PET Scan and PET-CT Fusion PET scan, or Positron Emission Tomography, is a powerful tool for detecting several types of cancer.  It is useful for the accurate detection of cancer spread in patients with an established diagnosis of cancer, or for the noninvasive evaluation of nodules detected by chest x-ray or CT.  PET works by having the ability to detect sites of high metabolic activity.  Since many cancers have significantly higher metabolism than normal tissues or noncancerous masses, PET allows sensitive detection of even small cancers.  These images demonstrate the power of PET-CT Fusion in identifying spread of tumor, in this case, spread of melanoma to a patient's liver.

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