Term
| How much biological damage due to x-rays is the result of indirect action? |
|
Definition
| 2/3 of damage is due to indirect action. |
|
|
Term
|
Definition
| G1, S (DNA synthesis), G2, and M (mitosis) |
|
|
Term
What phase of the cell cycle are cells most radiosensitive?
Most radioresistant? |
|
Definition
| most sensitive in M, most resistant in S |
|
|
Term
| What types of cells are the most radiosensitive and the least? |
|
Definition
| Cells that are rapidly dividing are most radiosensitive and highly differentiaed and/or nonproliferating cells are the least radiosensitive. |
|
|
Term
Define Oxygen Enhancement Ratio
What is a typical value. What does it mean. |
|
Definition
| Ratio of the dose to hypoxic cells / dose to oxygenated cells that cause the same amount of biological damage. Typical values are 2-3. This mean oxygenated cells are 2-3 time more sensitive to radiation. |
|
|
Term
|
Definition
| Linear Energy Transfer - enegy transfer per unit length of track (keV/um) |
|
|
Term
| What is the value of LET for x-rays? |
|
Definition
|
|
Term
|
Definition
Relative Biological Effectivness
RBE = Dose of 250 keV x-rays / Dose of test radiation that produces the same biological effect. |
|
|
Term
| How does RBE vary with LET? |
|
Definition
| RBE increases with LET up to about 100 keV/μm, then RBE falls off due to "overkill" |
|
|
Term
| Biological effects of radiation depend on |
|
Definition
| total dose absorbed and radiation type |
|
|
Term
|
Definition
It quantifies biological damage by different types of radiation. It equals the absorbed dose times the radiation weighting factor.
H = D * ωR |
|
|
Term
| What are the values for radiation weighting factors. |
|
Definition
x-rays and gamma rays - 1
protons - 2
neutrons - 2.5 to 20 depending on energy
alpha particles - 20 |
|
|
Term
| What is the LD50 for adults without medical intervention? |
|
Definition
|
|
Term
| Describe the different syndromes of acute radiation syndrome. |
|
Definition
Hematopoietic - 2-10 Gy - Blood elements decline in 2-3 weeks.
Gastrointestinal - > 10 Gy - Loss of gastrointestinal lining. Results are lethal - 5-10 days
Neurovascular or CNS - > 50 Gy -changes in the brain blood vessels - death in 1-2 days |
|
|
Term
| Describe deterministic effect |
|
Definition
| An effect that has a threshold, above which the effect occurs. As the dose increases, the effect becomes worse. |
|
|
Term
| What is the practical threshold dose for deterministic effects in diagnostic radiology? |
|
Definition
|
|
Term
| What are some examples of deterministic effects? |
|
Definition
| skin reactions, radiation induced cataracts, sterility |
|
|
Term
Threshold dose for transient erythema,
erythema, dry desquamation, moist desquamation, necrosis? |
|
Definition
transient erythema > 2 Gy
erythema - 5-10 Gy, dry desquamation - 10 Gy, moist desquamation - 15 Gy, necrosis - > 15 Gy |
|
|
Term
| At what skin dose does temporary epilation occur? Permanent epilation? |
|
Definition
| Temporary 3-5 Gy, Permanent > 7 Gy |
|
|
Term
| Tissue weighting factors for calculating effective dose are defined where? |
|
Definition
|
|
Term
| What is the current ICRP dose threshold for radiation induced cataracts? |
|
Definition
| 0.5 Gy for acute and chronic exposure |
|
|
Term
| What is the threshold dose for sterility in men? |
|
Definition
temporary - 2.5 Gy
permanent - 5 Gy |
|
|
Term
| What is the threshold dose for permanent sterility in females? |
|
Definition
6 Gy, but it's age dependant.
12 Gy prepubertal to 2 Gy premenopausal |
|
|
Term
| What are the 4 stages of ARS? |
|
Definition
| 1) Prodromal stage, 2) latent phase, 3) manifest illness, 4) recovery or death |
|
|
Term
| What are the teratogenic effects during the pre-implantation phase? |
|
Definition
| Pre-implantation occurs from fertilization to day 9. The cells are undifferentiated. Either too many of them die from the radiation leading to failure to implant and embryo death or the damaged cells are replaced and the embryo develops normally. "All or nothing" effect. |
|
|
Term
| What are the teratogenic effects during organogenesis? |
|
Definition
| Organogenesis runs from week 2 to week 8. Major internal organs are formed. Radiation may result in malformations - microcephaly being the most common, also general growth retardation can occur. |
|
|
Term
| What are the teratogenic effects during the fetal growth stage? |
|
Definition
| Fetal growth stage is from week 8 until term. The most sensitive period is from week 8 to week 15. Mental retardation and permanent growth retardation are the most common detrimental effects. |
|
|
Term
| After 15 weeks, what is the most significant radiation related risk to the fetus? |
|
Definition
| Excess risk of childhood cancer, approximately 6% per Gy. |
|
|
Term
|
Definition
| The dose required to double the incidence of spontaneous mutations. Doubling dose is thought to be 1-2 Gy in humans for low dose rate exposures. |
|
|
Term
| Below what dose are fetal effects not likely to occur? |
|
Definition
|
|
Term
| What is the hereditary risk (genetic) for radiation exposure? |
|
Definition
|
|
Term
| What is the excess cancer mortality for low dose and low dose rate radiation? |
|
Definition
|
|
Term
| What was the dose threshold for cataracts? Acute and chronic exposure? |
|
Definition
|
|
Term
| What is the primary concern with radiation below 2 Gy? |
|
Definition
|
|
Term
| What are the stochastic risks from radiation exposure? |
|
Definition
| carcinogenesis and hereditary effects |
|
|
Term
| The most radiosensitive organs are |
|
Definition
| bone marrow, breast, stomach, lungs, and colon |
|
|
Term
| What is DDREF. What is it's value. |
|
Definition
Dose and Dose Rate Effectiveness Factor
DDREF = 2
Used for converting high dose and dose rate risk estimates into low dose and dose rate risk estimates. |
|
|
Term
| The most important factor in determing the risk of cancer. |
|
Definition
| The age of the exposed individual. |
|
|
Term
| Children are approximately ____ times more radiosensitive than retired adults. |
|
Definition
|
|
Term
| For an A/P projection, the embryo dose is about ____ of the entrance air kerma. |
|
Definition
|
|
Term
| What are the four R's of radiobiology? |
|
Definition
| Repair, Repopulation, Redistribution, Reoxygenation |
|
|
