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16 Cards in this Set

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What is LET?
Linear Energy Transfer, it is the energy transferred per unit of track length in keV/µm
it is an average as the number of ionizations in any segment can vary greatly
Characteristics of low LET
sparsely ionizing radiations (photons, xrays, gamma)
travels long distance through tissue
higher energy radiation
Characteristics of high LET
densely ionizing radiations (alpha, N,P)
travels short distance through tissue
lower energy radiation
Oxygen effect has significant effect on ___ LET radiation and little or none on ____LET radiation.
Oxygen effect has significant effect on LOW LET radiation and little or none on HIGH LET radiation.
What is RBE?
Relative Biological Effectiveness
how is it measured?
A dose of radiation is compared to a "benchmark" dose of 250 keV x-rays as a ratio: dose of 250 keV xrays/ dose of any radiaton = RBE
What is optimum LET and why?
RBE increases with LET to about 100 keV/micrometer because ionizations at this level are at 2nm which is the diameter of a DNA helix
what is the dosage called above this level?
OVERKILL
Name the 5 factors effecting RBE?
1. radiation quality (LET)
2. Radiation dose
3. number of dose fractions
4. Dose rate
5. Biological system or endpoint
What is the law of Bergonie and Tribondeau? which is one of the most important concepts in radiobiology
Ionizing radiation are most effective against cells that are:
1. actively mitotic
2. undifferentiated
3. divide rapidly
4. have a long dividing future
What are the units for measuring absorbed radiation dose?
Rems and Sieverts, 100 rems = 1 Sieverts
For the purposes of radiation protection there is assigned a Radiation Weighting Factor or quality factor Q. state the factors for 4 levels of radiation
Alpha - 20
High energy protons - 10
Thermal neutrons - 2
Beta, gamma, X - 1
State the occupational dose limits for
1. Whole body
2. organ, skin, extremities
3. lens of the eye
1. Whole body - 5 rem/yr
2. organ, skin, extremities - 50 rem/yr
3. lens of the eye - 15 rem/yr
What does ALARA stand for?
As Low As Reasonably Achievable

What is the ALARA philosophy for occupational dose limits?
10% of NRC limits
What is the enhancement ratio for radiosensitizers?
Dose in rads to kill 63% w/o sensitisizer/dose in rads with sensitizer = Enhancement ratio
Over what # indicates a substance has radiosensitive properties?
1
What is the only radiosensitizer that we are really concerned with?
oxygen
What is the most effective radioprotector?
sulfhydryl compounds
what is the problem with using them?
an effective level ingested is toxic to the body
What is the dose reduction factor?
dose to kill 63% with protector/dose to kill 63% w/o protector where a DRF greater than 1 indicates protective qualities
it has protective qualities