Radiation biology Flashcards
What is exposure (X)?
Amount of electrical charge produced by ionizing EM radiation per mass
X = Q/m
How is exposure measured? (equation and labels)
X = Q/m
Roentgen or C/kg
1 Roentgen = 2.58 x 10-4 C/kg
What is the absorbed dose?
energy of ionizing radiation absorbed per unit mass by a body.
Product of absorbed dose averaged over tissue or organ and the weighting factor (Wr) for the type and energy of radiation used.
How is absorbed dose measured? (Equation and labels)
D = Energy/mass
Gy or rad
1 Gy = 100 rad
1 rad = 0.01Gy
What is the equivalent dose (H)?
Differing ionizing radiations will produce different biological damage. Equivalent dose accounts for the difference in different radiation types by applying a weighting factor
How is equivalent dose calculated? (Equation and labels)
What are different weighting factors for different radiation types?
H = D (absorbed dose) x Weighting factor Sv and rem X ray, gamma/beta rays = 1 Protons = 2 Neutrons = 2.5-20 Alpha = 20
What is the effective dose?
Biologic tissues vary in sensitivity to effects of ionizing radiation. Tissue weighting factors were developed as part of radiation protection protocol.
(Sum of products of equivalent dose x weighting factor for each tissue exposed)
How is effective dose measured?
Sum of the products of the equivalent dose (weighting factor X absorbed dose) to each of the organ/tissue irradiated and the corresponding weighting factor for that organ or tissue.
Expressed in Sv and rem
How do you convert Gy to rad?
1 Gy = 100 rad
1 rad = 10mGy (0.01Gy)
How do you convert Sievert to rem?
1 Sv = 100 rem
1 rem = 10mSv (0.01Sv)
How does Sievert relate to Gy?
Sievert is equivalent dose - multiply the absorbed dose (Gy) by the weighting factor of the ionzing radiation (1 for rads, 20 for alpha particles)
What is a deterministic effect? (3 criteria)
1) Severity increases with dose
2) Practical threshold – above which loss of tissue function can occur. Below this level - effects will not occur
3) Probability of occurrence increases with dose (cataracts)
What is a stochastic effect (3 criteria)
1) Severity is independent of dose
2) No threshold
3) Probability of occurrence increases with dose (cancer)
Which tissues wlil have a higher effective dose? (Higher weighting factor)
Breast, bone marrow, colon, lung, stomach, gonads
What is direct vs indirect radiation?
A) Direct – particulate radiation (alpha particles, neutrons)
1) Directly interacts with critical targets in the cells and causes damage
B) Indirect – diagnostic radiology (xrays)
1) Radiation will interact with water (not important portions of the cells) that will produce free radicals, and these radicals to damage to the critical portions of the cells.
