Radiation biology

Question 1

What is the LD 50/60 in humans?

Answer 1

4 Gy

Question 2

What are the tissue weighing factors for the most sensitive tissues (and some others)?

Answer 2

0.12 - lung, stomach, colon, bone marrow, BREAST, remainder (other intraabdo organs, heart, LNs, muscles, prostate, uterus)
0.08 - Gonads
0.04 - Liver, oesophagus, bladder, thyroid
0.01 - Skin, cortical bone, brain, salivary gland

Question 3

High dose radiation and their consequences (and rough dose range)

Answer 3

3-5 Gy - loss of viable bone marrow, 50% death within 60 days (LD 50/60)
5-12 Gy - severe GI damage and death within weeks
50 Gy - neurovascular syndrome, death within days

Question 4

What dose-response model does the BEIR VII report recommend for calculating the risk of solid tumor induction from ionizing radiation?

Answer 4

Linear, no threshold

Question 5

What is the most sensitive time for mental retardation in a fetus?

Answer 5

8-15 weeks (2 - 4 months)

Question 6

What is the most sensitive time for malformation in a fetus?

Answer 6

3 -8 weeks

Question 7

What is the most sensitive time for growth retardation in a fetus?

Answer 7

4th week to term (but mostly in 1st trimester up to 12 weeks)

Question 8

What is the likelihood of inducing childhood cancer per mSv in fetal irradiation?

Answer 8

1 in 10,000 per mSv/mGy of exposure for CHILDHOOD CANCER

Question 9

What skin reaction would you expect at a dose of 2-5 Gy?

Answer 9

Transient erythema (onset 2-24 hours)
Transient epilation with no long term effects

Question 10

What skin reaction would you expect at a dose of 5-10 Gy?

Answer 10

Transient, prolonged erythema (at higher doses)
Epilation, permanent partial epilation

Question 11

What skin reaction would you expect at a dose of 10 - 15 Gy?

Answer 11

Prolonged erythema, desquamation (would heal), telangiectasia +/- dermal atrophy or induration. Weak skin
Permanent epilation

Question 12

What skin reaction would you expect at a dose of >15 Gy?

Answer 12

Erythema, dermal atrophy, desquamation, ulceration from non-healing desquamation, late skin breakdown
Permanent epilation

Question 13

What is the dose threshold for cataract induction?

Answer 13

0.5 Gy cumulative dose
Several year latency period, develops at posterior pole and migrates anteriorly

Question 14

How do you calculate the fetal dose in XR exams?

Answer 14

Using the percentage depth dose (PDD), usually 25% in 1st and 2nd trimester. Fetal is usually 8cm below the skin surface
Fetal dose (mGy) = ESD x 0.25

Question 15

What is the lifetime risk of fatal carcinogenesis per 1 Sv?

Answer 15

~5-10% per Sv

Question 16

What is the dose limit to skin?

Answer 16

500mSv

Question 17

What is the lens dose limit?

Answer 17

20mSv per year, 0.5Gy threshold for cataract formation