Radiation Oncology/Radiobiology/Basic Radiobiology

4 R's of Radiobiology
• Repair
• Reassortment
• Repopulation
• Reoxygention
Basic RadiobiologyEdit
Here I would like to explain the basic concepts in radiobiology in a way, I never forget and in a way that you certainly understand. I am positive that if you understand, then you will never forget as well:
OK!
Deep Breath! :D
1. Remember the concept of Logarithm!
When base is 10:
So
What does that do with radiobiology and radiation oncology?!
2. Think about fractional cell kill!
What the hell is that then?!
Let's say each Gy of dose kill 90%(0.9) of cells —> 10% will be left —> 0.10 will be left
then after the second next Gy —> 0.9x0.10 will be left
or 0.9x(10.9)
and then after the third dose of Gy —> 0.9x0.9x(10.9) … etc would be the amount of cells that will be killed.
That's were the log comes in! After certain number of dose==>
0.9^{certain number} x (10.9) should be calculated.
or
0.9^{certain number}  0.9 ^{certain number+1} should be calculated
ɑ/β ratioEdit
AlphaEdit
 Intrinsic radiosensitivity of the cells
 Defined as how many logs (to the exponential base “e”) are killed (sterilized) per gray, in a “non repairable” way.
BetaEdit
 It reflects cell repair mechanisms.Repairable portion of the radiation damage, requiring 6 h or more for complete repair.
 It can be regarded as the result of two chargedparticle tracks passing through a sensitive target in the cell nucleus in less than 6 h, so this term has to be multiplied by d squared.
Alpha/BetaEdit
 Think about small alpha/beta ==> So beta should be big ==> that means repair mechanisms is large ==> that means time to carry out repair should be long ==> that means cell cycle is long ==> that means tissue is slowly proliferating and evetually it's a late reacting tissue.
 The shoulder will be broad too.
Famous rule of Bergonie and Tribondeau:
 They did experiments on testis Rat.
 Radiosensitivity of cells or tissues is correlated with the frequency of mitoses which they undergo ==> poorlydifferentiated and fastproliferating tissues are more radiosensitive than welldifferentiated and slowproliferating tissues
Also look at Radiobiology and Lung