Late Effects - Student Notes

Which 2 factors are plotted on a dose response curve?

Dose vs biologic response

What is the term for a deterministic dose response curve?

Nonstochastic

What is the term for a probabilistic dose response curve?

Stochastic

Which curve is dose dependent - i.e., has a threshold dose?

Nonstochastic (determined by threshold dose)

What happens to the biologic effect as dose increases on a nonstochastic dose response curve?

Effect severity increases with dose

What happens to the biologic effect as dose increases on a stochastic dose response curve?

Dose increase = probability that effect will occur increases

What is the most common late (chronic) stochastic biologic response to radiation?

Cancer

Why is there no early stochastic somatic biologic response to irradiation?

Not enough time for probability of effect occurrence to build

What is the term for a genetic mutation in future generations due to irradiation of parental gonads prior to conception?

Mutagenesis

What is the term used to describe disease within a population?

Epidemiology

Which type of response curve is demonstrated in the image?

Cell survival curve

Which type of curves are demonstrated in the image?

Dose Response Curves

What is the use of a dose response curve?

1. Set dose limits for occupational radiation workers

2. Room design for general public safety

What are some examples of late radiation effects?

1. Cataracts (nonstochastic)

2. Leukemia (stochastic)

3. Genetic mutations

Describe this dose response curve

1. Linear

2. Nonstochastic (determined by threshold dose)

3. Severity of effect increases as dose increases

What are some biologic effects which would be represented by this dose response curve?

1. Erythema

2. Hematologic changes

3. Epilation

4. Desquamation

5. ARS

Describe this dose response curve

1. Nonlinear

2. Nonstochastic (determined by threshold dose)

3. Severity of effect increases as dose increases (in straight line portion)

What happens to the dose response in the tail, straight line, and shoulder portions of the curve?

1. Tail indicates recovery at lower doses

2. Straight line indicates sharp increase in biologic response

3. Shoulder indicates recovery or death

What are some biologic effects which would be represented by this dose response curve?

1. Cataracts

2. Radiation therapy (fractionated & pronated)

Describe this dose response curve

1. Linear

2. Stochastic (not dose dependent)

3. No threshold

4. Probability of effect increases as dose increases

What is significant about this particular dose response model?

1. Assumes no safe radiation dose

2. Most conservative model

3. All dose limits in use today are based on this curve

What type of curve is represented by this image and what exactly is being estimated by this curve?

1. Linear quadratic model

2. Estimates risk from low dose and/or low LET radiation

What are some examples of biologic effects that would be represented by this dose model?

1. Leukemia

2. Breast cancer

3. Thyroid cancer

4. Genetic effects

What is the term for biologic effects from a fetus irradiated in utero?

Teratogenic (congenital malformations, decreased birth weight, childhood malignancies)

Irradiation of parental gonads resulting in birth defects of the child - somatic or genetic?

Genetic

What is the absolute risk of radiation-induced carcinogenesis according to the Committee on the Biologic Effects of Radiation (BEIR)?

1. 5 x10^-4 rem^-1

2. 1 in 50,000 for every rem

Which radiation induced cancer has the shortest latent period?

Leukemia

Which late non-stochastic radiation effect is also dependent on age?

Cataracts

What was the main biologic effect observed in children after the Chernobyl disaster?

Thyroid cancer (ground I131, cows eating grass, contaminated milk)

What is the estimate of human life span shortening from irradiation?

10 days for every rad absorbed

What is the term for the prediction of the number of excess (radiation-induced) cancers that will increase in a given population as age increases and natural cancer occurrences increase?

Relative risk

What is the threshold dose of radiation-induced cataractogenesis?

1. 2 Gy - threshold dose of 15 years

2. Age dependent

Which trimester of pregnancy is the most radiosensitive period?

1st trimester

What is the definiton of gestation?

Conception to birth (9 months)

What is the relationship between gestation and radiosensitivty?

1. As gestation increases, radiosensitivity decreases

2. Inverse relationship

What are the 3 stages & time frames of embryonic (birth defect0 risk after irradiation?

1. Preimplantation (0-9 days after conception)

2. Organogenesis (10 days - 12 weeks)

3. Fetal (12 weeks - term)

What is the fetal dose threshold beyond which medical abortion should be considered?

1. 0.1 Sv (1000 mSv) directly absorbed by fetus

2. Significant radiation exposure from fluoroscopy-guided interventional pelvic procedures or radiation therapy

During which time period of gestation is the fetus most susceptible to CNS malformations?

8-25 weeks (organogenesis)

Which type of malformations are most common during 3-20 weeks of gestation?

Skeletal malformations

What is the most likely result of significant radiation exposure to the fetus in the first 2-3 weeks of gestation?

Embryonic abortion

What is the term for death of the fetus prior to birth?

Prenatal death (fetal death)

In which stage of gestation are malformations or radiation-induced congenital abnormalities most likely to occur?

Organogenesis

What radiation-induced congenital abnormalities are most likely during organogenesis?

Mental retardation & microcephaly

What is the term for the dose causing an increase by 2 times in the number of spontaneous mutations in a given generation?

Doubling dose

What is the radiation equivalent doubling dose for humans?

1.56 Sv (156 rem)

What is considered a safe dose of radiation?

No radiation dose is considered safe