4 R's of Radiobiology
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:
Deep Breath! :D
1. Remember the concept of Logarithm!
When base is 10:
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
and then after the third dose of Gy —> 0.9x0.9x(1-0.9) … etc would be the amount of cells that will be killed.
That's were the log comes in! After certain number of dose==>
0.9certain number x (1-0.9) should be calculated.
0.9certain number - 0.9 certain number+1 should be calculated
- 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.
- 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 charged-particle 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.
- 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 ==> poorly-differentiated and fast-proliferating tissues are more radiosensitive than well-differentiated and slow-proliferating tissues
Also look at Radiobiology and Lung