mahoney 5

Question 1

stochastic effect def***

Answer 1

• responses where probability of occurrence increases with dose
  
  • I.e. The HIGHER the dose, the GREATER the chance of effects
• Result from LOW RADIATION doses over LONG TIME

Question 2

Deterministic effect def (nonstochastic)***

Answer 2

• Severity of response INCREASES with dose
  
  • the higher the dose, the more severe the response
• Have Threshold dose which needs to be exceeded before response is seen and severity of resposne proportional to dose
• example: Radiation sickness causes death to hematologic, GI, and nervous system
  
  • occurs eqrly over hours or days

Question 3

Law of Bergonie and Tribondeau

Answer 3

• Sensitivity of tissues depends upon proliferative capacity (rapidly dividing cells more sensitive than slowly dividing cells) and differentiation (full differentiated cells less senstivit)
• Most sensitive = bone marrow > lymphocytes > GI
• More resistant = CNS

Question 4

what are the 4 phsyical factors affecting radiosensitivity

Answer 4

• Linear energy transfer (LET)
  
  • measure of amount of energy transferred along path of radiation
• Relative biologic effectiveness
  
  • effectiveness of one form of radiation compared to another
• Protraction (for TX)
  
  • radiation dose to neoplasm is delivered continuously, but at a lower dose rate
• Fractionation (for TX)
  
  • same radiation dose rate to neoplasm is delivered to equal fractions, each separated by period of time

Question 5

Direct effects of radiation

Answer 5

• Radiation interacts directly with a molecule like DNA
• accounts for small fraction of damage at low LET, but most of damage at HIGH LET

Question 6

indirect radiation effects

Answer 6

• Caused by free radicals formed from ionizing radiation interacting with body
• free radicals migrate from the initial site of ionization of DNA, transfers its excess energy and disrupts bonds
• accounts for most damage at LOW LET

Question 7

cumulative annual dose for an average dose

Answer 7

1/10 of (age in yrs X 1 rem

• for 40 yrs old, dose should not exceed 4 rem or 4000mrem

Question 8

Dose Limits

Answer 8

• DL: the amount of radiation that if received annually runs the risk of death to 1:10,000

Question 9

Limits for occupationally exposed to radiation

Answer 9

• annual effective dose: 50mSv (5 rem)
• cumulative annual effective dose: 10mSv (1rem) x age
• Equivalent annual dose for skin, hands, feet: 500mSv (50 rem)
• Equivalent annual dose for lens of eye: 150mSv (15 rem)
• Pregnant worker: 5mSv (.5rem) for the 9 months of pregnancy
• Limit for children less than 18 = 1mSv (100mrem) for annual exposure