7 Radiobiology/Patient Dosimetry

Question 1

What is the definition of Direct action?

Answer 1

Occurs when Compton/photoelectrons directly ionize a target molecule.

Question 2

What is the definition of indirect action?

Answer 2

Occurs when Compton/photoelectrons interact with water to produce a (free) hydroxyl radical.

Question 3

What is the definition of Free radicals?

Answer 3

Chemically reactive molecules with unpaired electrons produced by ionizing radiation.

Question 4

What is the definition of Radiobiology?

Answer 4

Radiobiology is the study of the effects of ionizing radiation in cells and animal models.

Question 5

What is Cell cycles for mammalian?

Answer 5

Mitosis (M), G1, DNA synthesis (S), and G2.

Question 6

What are the most sensitive stages in cell cycles?

Answer 6

In M and G1 and most resistant during S.

Question 7

What is the definition of somatic effect?

Answer 7

Cells can result in the induction of cancer (fatal and nonfatal). Induction of cancer by radiation takes years and decades to develop.

Question 8

What is the definition of the hereditary effect?

Answer 8

–Damaged sperm and eggs (i.e., germ cells) can result in (mutations), are sometimes called genetic effects.

Question 9

oxygen enhancement ratio (OER)

Answer 9

(doses of hypoxic irradiation)/(dose of aerated irradiation) that produces the same amount of biologic damage.

Question 10

Linear energy transfer (LET)

Answer 10

The energy transferred per unit length of track.

Question 11

Relative biologic effectiveness (RBE)

Answer 11

The ratio D250/Dtest, in which D250 is the dose of 250-kV x-rays and Dtest is the dose from the test radiation.

Question 12

Uses of Relative biologic effectiveness (RBE)

Answer 12

To compare the ability of different types of radiation to cause biologic damage.

Question 13

Equivalent dose (H) as sievert (Sv).

Answer 13

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.

Question 14

Deterministic effects

Answer 14

• 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.

Question 15

Carcinogenesis effects

Answer 15

A stochastic effect of radiation, meaning random or probabilistic.

Question 16

The effective dose (E)

Answer 16

Obtained by taking into account the equivalent dose to all exposed organs, as well as each organ’s relative radiosensitivity.

Question 17

The organ weighting factor w

Answer 17

A measure of the relative organ radiosensitivity for the induction of stochastic effects.

Question 18

The most radiosensitive organs

Answer 18

The red bone marrow, colon, lung, breast, and stomach.

Question 19

Moderately sensitive organs

Answer 19

The bladder, esophagus, liver, and thyroid.

Question 20

Lower-sensitivity organs

Answer 20

The skin, bone surfaces, brain, and salivary glands.

Question 21

What fraction of cell damage most likely results from direct action of x-ray radiation?

Answer 21

1/3 is direct, and the remaining 2/3 is indirect damage.

Question 22

A whole-body dose of ∼100 Gy

Answer 22

Kill in 1 to 2 days

Question 23

A whole-body dose of ∼10 Gy

Answer 23

Kills in 5 to 10 days due to loss of epithelial lining of the
gastrointestinal tract (i.e., GI syndrome).

Question 24

A whole-body dose of ∼2 to 5 Gy

Answer 24

Sterilizes dividing precursor stem cells, which reduces

circulating blood elements within 2 or 3 weeks (i.e., hematopoietic syndrome).

Question 25

A whole-body dose of 1 Gy

Answer 25

Reduce the number of lymphocytes.

Question 26

For skin doses

Answer 26

• 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.

Question 27

Cataractogenesis doses

Answer 27

–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.

Question 28

Sterility doses

Answer 28

• 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.

Question 29

A common backscatter value used in radiology is

Answer 29

1.4.