7 Radiobiology/Patient Dosimetry Flashcards
What is the definition of Direct action?
Occurs when Compton/photoelectrons directly ionize a target molecule.
What is the definition of indirect action?
Occurs when Compton/photoelectrons interact with water to produce a (free) hydroxyl radical.
What is the definition of Free radicals?
Chemically reactive molecules with unpaired electrons produced by ionizing radiation.
What is the definition of Radiobiology?
Radiobiology is the study of the effects of ionizing radiation in cells and animal models.
What is Cell cycles for mammalian?
Mitosis (M), G1, DNA synthesis (S), and G2.
What are the most sensitive stages in cell cycles?
In M and G1 and most resistant during S.
What is the definition of somatic effect?
Cells can result in the induction of cancer (fatal and nonfatal). Induction of cancer by radiation takes years and decades to develop.
What is the definition of the hereditary effect?
–Damaged sperm and eggs (i.e., germ cells) can result in (mutations), are sometimes called genetic effects.
oxygen enhancement ratio (OER)
(doses of hypoxic irradiation)/(dose of aerated irradiation) that produces the same amount of biologic damage.
Linear energy transfer (LET)
The energy transferred per unit length of track.
Relative biologic effectiveness (RBE)
The ratio D250/Dtest, in which D250 is the dose of 250-kV x-rays and Dtest is the dose from the test radiation.
Uses of Relative biologic effectiveness (RBE)
To compare the ability of different types of radiation to cause biologic damage.
Equivalent dose (H) as sievert (Sv).
Quantifies biologic damage by different types of radiation.
is the absorbed dose (D) multiplied by the radiation weighting factor (wR) of the radiation, or H = D × wR.
Deterministic effects
- A deterministic effect has a threshold dose, below which the effect does not occur.
- When the threshold dose is exceeded, deterministic effects are possible.
- Deterministic effects also include cataract induction and induction of sterility.
Carcinogenesis effects
A stochastic effect of radiation, meaning random or probabilistic.
The effective dose (E)
Obtained by taking into account the equivalent dose to all exposed organs, as well as each organ’s relative radiosensitivity.
The organ weighting factor w
A measure of the relative organ radiosensitivity for the induction of stochastic effects.
The most radiosensitive organs
The red bone marrow, colon, lung, breast, and stomach.
Moderately sensitive organs
The bladder, esophagus, liver, and thyroid.
Lower-sensitivity organs
The skin, bone surfaces, brain, and salivary glands.
What fraction of cell damage most likely results from direct action of x-ray radiation?
1/3 is direct, and the remaining 2/3 is indirect damage.
A whole-body dose of ∼100 Gy
Kill in 1 to 2 days
A whole-body dose of ∼10 Gy
Kills in 5 to 10 days due to loss of epithelial lining of the gastrointestinal tract (i.e., GI syndrome).
A whole-body dose of ∼2 to 5 Gy
Sterilizes dividing precursor stem cells, which reduces
circulating blood elements within 2 or 3 weeks (i.e., hematopoietic syndrome).
A whole-body dose of 1 Gy
Reduce the number of lymphocytes.
For skin doses
- 2 Gy, transient erythema may occur in a matter of hours.
- 6 Gy produce erythema 1 to 2 weeks.
- 10 Gy can produce dry desquamation.
- > 15 Gy can produce Moist desquamation.
- ∼7 Gy, epilation can be permanent.
Cataractogenesis doses
–An acute dose of ∼2 Gy is required to produce a cataract.
–For chronic exposure, the threshold dose for radiation-induced cataracts is ∼5 Gy.
Sterility doses
- 0.2 Gy can produce a diminished sperm count.
–Doses above 0.5 Gy can result in azoospermia (temporary sterility).
–Sterility requires a single dose of ∼6 Gy in men.
–Permanent sterility can result from ∼3 Gy fractionated over a few weeks.
–The dose required for permanent sterility in the female ovaries is reported to be as high
as 12 Gy in prepuberty.
–Female permanent sterility results from a dose of ∼2 Gy for premenopausal women.
A common backscatter value used in radiology is
1.4.
