27. Radiation and bodies. Applications.

Question 1

Explain the phases of radiation damage

Answer 1

Phases of radiation damage:

1. physical phase (10^-17 - 10^-12 s): ionization
2. **chemical phase **(10^-10 - 1 s): free radical reactions
3. biological phase
   
   • hours: alteration in tissues
   • days - years: stomach-bowel cancer, damage haematogenesis, somatic damage

Question 2

Explain the characteristics of stochastic radiation damage refering to the diagram below. Which group might be affected by that particular kind of radiation damage?

Answer 2

Characteristics of stochastic radiation damage:

• threshold dose: none, any small dose can cause damage, probability proportional to absorbed dose (see diagram)
• reason for damage: abnormal cell mutations cause malignant tumors (cancer)
• affected group: personnel at workplaces using ionizing radiation, patients of X-ray and nuclear imaging investigations
• protection: severity is independent of absorbed dose, therefore probability of damage can only be minimized by applying very low doses

Question 3

Explain the characteristics of deterministic radiation damage refering to the diagram below. Which group might be affected by that particular kind of radiation damage?

Answer 3

Characteristics of deterministic radiation damage:

• threshold dose: yes, when dose is lower than threshold the probability of damage is 0. After threshold amount, the severity increases with increasing dose and reaches 100%
• reason for damage: death of cells (death of RBCs)
• affected group: patients in radiotherapy
• protection: severity dependent of absorbed dose, therefore if absorbed dose below threshold no risk

Question 4

Why do we need radiation protection? Answer refering to specific groups.** **

Answer 4

Tasks of radiation protection:

• justification
• detection of the **pollution **

For personnel:

• rule out deterministic effect
• reduction of stochastic effect on a rationally acceptable level:
  
  • ALARA principle
  • dose limits

For patients:

• cost-benefit principle
• measurement and documentation of patient’s dose levels

Question 5

What do equivalent dose and the associated weighting factor mean?

Answer 5

Equivalent dose (H):

effect of radiation (how much E absorbed) on a certain type of tissue (by unit mass). The absorbed dose is weighted by the radiation weight factor w_R

H_skin = w_α * D_skin,α + w_β * D_skin,β + w_γ * D_skin,γ

→ measured in Sievert [Sv] = [J/Kg]

w_R-radiation weighting factor:

characterizes radiation, shows how many times the radiation is more effective to cause biological effect than γ-radiation or X-rays

Question 6

What do effective dose and the associatied weighting factor mean?

Answer 6

Effective dose (E):

Expresses the biological damage of the individual tissue or organ of the body. The effective dose is the sum of the weighted equivalent doses in the body.
E = w_T + H_T

→ measured in Sievert [Sv] = [J/Kg]

w_T – tissue weighting factor:

represents the relative contribution of that organ or tissue to the total damage in case of stochastic effects resulting from uniform irradiation of the whole body

→ gonads (w_T = 0.2) 20 times more sensitive than the skin (w_T = 0.01)

Question 7

What does ALARA stand for? What do the two curves in the diagram below mean?

Answer 7

ALARA = as low as reasonably achievable

principle to optimize radiation protection

• *blue:** shows the cost of the protection → better protection→ lower damage
• *red:** shows the cost of treatment when the worker isn’t protected well →

Question 8

What are dose limits? List the dose limits set according to the ALARA principle. Compare it with some dose values in radiotherapy

Answer 8

Dose limit:

maximum dose with acceptable level of **risk **

for personnel at radiation workplace:

• EU (USA): 20 (50) mSv/year
• 100 mSv/5 years
• 400 mSv/life time

dose values in radiotherapy:

• conventional X-ray: 0.2 - 1 mSv
• CT scan: 2 - 8 mSv
• radiotherapy: 45 - 60 Gy (in 2 Gy fractions)

Question 9

Name 3 methods to decrease the exposure from radition source outside the body

Answer 9

Methods:

• increase the distance the source
• decrease the exposition time
• application of shielding

Question 10

Which radiation is the most dangerous if the source is 1) outside the body or 2) inside the body? Explain.

Answer 10

Risk depends on the type of radiation:

1. If the source is outside the body, γ‐ or X‐radiation is the most dangerous (because of high effective range).
2. If the isotope is incorporated (by inhalation or by swallowing), α‐radiating isotopes are the most dangerous (all the radiation is absorbed in the body tissues).