Physics book

Question 1

What is the equilvalent dose?

Answer 1

Dose x Weight factor

Question 2

what is the weighting factor for different molecules

Answer 2

1 for electrons and photons (gamma and x-ray)

5-20 for neutrons

5 for protons

20 for alpha

Question 3

What is the effective dose?

Answer 3

Equilvalent dose x tissue factor

Sv

Question 4

What is a deterministic effect? Stochastic effect?

Answer 4

1. Deterministic
   
   1. there is a threshold (burns, gut necrosis, cataract)
   2. Severity is dose related
2. Stochastic - there is no threshold - Shit happens = cancer
   
   1. Severity is not related to dose
   2. Probability increases with dose
   3. heritable effects and carcinogenesis

Question 5

What is LET and what does it stand for?

Answer 5

Linear energy transfer - amount of energy deposited per unit path

High LET: Neutrons, protons, alphas, heavy ions

Low LET: Photons, Gamma rays, electrons, positrons

Question 6

What is the RBE?

Answer 6

It is the relative capability of radiation with differeing LETs to produce a biologic reaction.

RBE = Dose of 250 kV x-ray/Dose in Gy of test radiation

Ex: A reaction is produced by 5 Gy of test radiation. It takes 10Gy of 250kVp x-rays to produce the same reaction…what is the RBE?

10/5= 2 RBE= 2

Question 7

As LET increase RBE does what?

Answer 7

Increase…to a point. Then any more LET is just over kill. Can kill shit twice.

Question 8

What is the difference between Direct and indirect radiation?

Answer 8

1. Direct
   
   1. Acts on DNA
   2. Most likely for High LET radiation
2. Indirect
   
   1. Acts on water creating free radicals which then damage DNA
   2. Low LET
   3. This process is promoted by the presence of O2

Question 9

What are the most sensitive phases of the cell cycle?

Answer 9

M>G2>G1>S

G1 has the most variable length cause faster cell turn over.

Question 10

What part of the GI tract is most sensitive to radiation?

Answer 10

Small bowel.

Question 11

What is the most sensitive cell in blood?

Answer 11

lymphocytes (0.25 Gy is enough to depress circulating)

Question 12

What are the phases of Acute radiation syndrome and when do they occur?

Answer 12

1. Bone marrow
   
   1. >2gy
   2. Latent period 1-6weeks
2. GI
   
   1. >8Gy
   2. Latent period 5-7 Days
   3. Death in 2 weeks from sepsis
3. CNS
   
   1. 20-50 Gy
   2. Latent period 4-6 hours
   3. Death within 3 days

Question 13

What is a marker of severity of radiation exposure and is a poor prognosis?

Answer 13

Early vomitting… the earlier the worse.

Question 14

What is the L50/30 in radiation exposure and what dose it mean?

Answer 14

Lethal dose for 50% of the people in 30 days

3-4Gy

Question 15

Radiation effect of the fetus:

1. First two weeks is called what and what happens when exposed to 50-100mGy?
2. 8-15 weeks is considered what as a period of sensistivity? What happens to the fetus?
3. After 15 weeks what happens?

Answer 15

1. Implantation - death at 50-100mGy
2. 8-15 weeks is the most sensitive time - Reduced head diameter and mental retardation
3. Brain is less sensitive to radiation

Question 16

What is the difference between senile cataracts and radiation induced cataracts?

Answer 16

Senile involve the anterior lens

Radiation induced involve the posterior

Question 17

What is the threshold for cataracts?

Answer 17

2.5Gy acute

Annual = 150mSv

Question 18

The majority of biologic change is mediated by what?

Answer 18

Free radicals

Question 19

Risk of radiation induced cancer for adults and kids?

Answer 19

Adults = 4-5% per Sv

15% per Sv in kids

Question 20

What is the greatest source of exposure to ionizing radiation for the general population in the US?

Answer 20

Medical imaging - CT