Rad Bio
Chapter 5 Lecture Notes
Long-term radiation effects (low doses over a long period of time) for occupational exposure.
Epidemiology (p. 70) – the science that examines the incidence, distribution, and control of disease in a population. We’ll observe radiation-induced cancer from the following sources:
1. atomic bomb survivors
2. medically exposed patients
3. occupationally exposed personnel
4. populations who receive high background exposure
Occupational exposure is measured by a linear, non-threshold response curve
Relative risk (p. 71) – theory that after the latent period, risk for obtaining cancer is related to the natural age-specific cancer risk for that population. So if a 17 year old and a 68 year old are induced with a dose to the lens of the eye, the 68 y/o will have a higher “relative risk” for obtaining cataracts after the latent period.
Absolute risk - theorizes that as a person ages, their risk for obtaining cancer increases. Remember this is due to life-long accumulation of small doses of radiation. Just like life-long smoking – increased risk for the person who’s been smoking 20 years compared to 1 year.
Relative risk example (p. 75) – ranges from 1 to 10, with long-term effects ranging between 1 and 2 (1 being no effect at all). A relative risk of 1.5 means there has been a 50% increase of incidence in the irradiated group compared to the non-irradiated group.
1.5 = 150
100
(p. 74 example)
Relative risk = Observed cases
Expected cases
400 = .003 (incidence of irradiated people developing leukemia) - observed
150,000
120 = .0012 (incidence of leukemia in non-irradiated people) – expected
100,000
.003 = 2.5 (2 and ½ times more likely to develop leukemia if you were irradiated)
.0012
Absolute risk example (p. 77) – need to know two different dose levels to calculate.
Risk for radiation induced breast cancer = (6 cases/10-6 persons/rad/yr)
Test = (10-4 persons)(1rad)(15yr)
Multiply together = .000006 x 10-4 (or 10,000) x 1 x 15 = 0.9
Excessive risk – found when you observe the number of incidences in irradiated population and subtract the number of normally expected cases.
Excessive risk = observed – expected (example p. 77)
(p. 78) Radiation induced malignancies can be discovered shortly after exposure, but ionizing radiation can cause damage that does not manifest itself for years or even decades. These include
1. leukemia
2. skin carcinoma
3. thyroid cancer
4. breast cancer
5. osteosarcoma
6. lung cancer
Leukemia (p. 80) – studies taken from atomic bomb survivors, patients treated with radiation for ankylosing spondylitis, and radiologists.
1. one of the most rare diseases, but also one of the most frequently observed radiation-induced cancers.
2. responsible for about 1/6 of fatalities from radiocarcinogenesis
3. can be acute or chronic
4. can originate in the lymph tissue or the bone marrow
5. incidence of leukemia from radiation decreases with age
6. linear non-threshold dose response
7. latent period of 4-7 years
8. at-risk period of 15-20 years
Skin Carcinoma – studies taken from people receiving radiation treatment for acne and ringworm who developed skin cancer later.
1. follows a threshold dose-response curve
2. latent period of 5-10 years
3. 5-2,000 rads = relative risk of 4 to1
4. 10,000 rads and above = relative risk of 27 to 1
5. not present today in radiology personnel
Thyroid Cancer (p. 81) – studies taken from infants treated with radiation for thyroid enlargement and people who were children at the time of the atomic blasts.
1. responsible for 12% of deaths attributed to radiation induced malignancies
2. females have 3-5 times greater risk for thyroid Ca due to hormonal influences
3. papillary nodules – nipple like
4. follicular – cavity like
5. latent period for benign nodules = 5-35 yrs
6. latent period for malignant nodules = 10-35 yrs
7. linear non-threshold response curve
Breast Ca (p.81)
1. Low LET radiation which is age-dependent
2. women 15 y/o are 50 times more likely to develop Ca after an exposure of 10 rads than the 55 y/o range
3. linear dose-response relationship
4. latent period from 10-40 years
5. low doses received during mammography not proven to increase risk of Ca
Osteosarcoma (p. 82) – studies taken from watch-dial painters who used radioactive radium to make the watch dials luminesce in the dark.
1. overall relative risk of 122 to 1
2. linear quadratic dose-response
Lung Ca – studies taken from miners of uranium, who were exposed to inhalation of radon gas, which is a by product of decaying uranium.
1. alpha particles with high LET and RBE were the radiation source
2. linear non-threshold dose response
GSD (p. 85-86) – average calculated low gonadal dose received by the entire population to see effects in future generations. It assumes that this dose would have the same effect as the actual dose received by those who were exposed.
1. annual GSD is 130 mrem
2. background radiation makes up 102 mrem (78%)
3. medical radiation makes up 20 mrem (22%)
4. see chart on p. 87
Irradiation of the Fetus (p. 90)
1. doses up to 5 rads have not demonstrated any significant risk for congenital malformation or retarded growth
Pre-implantation stage – when sperm joins with egg
1. damage during this stage can cause prenatal death
2. occurs after doses of 5-10 rads
Major organogenesis stage – 2nd to 8th week after conception
1. CNS one of the most sensitive at low LET doses less than 25 rads
Fetal growth stage (beginning at day 45)
1. main anomalies seen are nervous system
2. damage in this stage may not manifest until later in life (i.e. behavioral changes, reduced IQ, or cancer)
Cancer in utero is up to three times more frequent following irradiation in the first trimester, compared to second and third. Annual occupational exposure limit for fetus is 0.5rem (measured with fetal badge)
Stochastic effects (p. 96) – occur randomly in nature, and are said to be nonthreshold. They measure the probability of occurrence of an effect rather than its severity.
Non-stochastic effects – require high doses of radiation to occur, and said to be threshold. Measures the severity of the effect, rather than the probability of occurrence.