# Basic 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:

OK!

Deep Breath! :D

1. Remember the concept of Logarithm!

When base is 10:

So

(2)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(1-0.9)

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==>

0.9 ^{certain number} x (1-0.9) should be calculated.

or

0.9 ^{certain number} - 0.9 ^{certain number-1} should be calculated

# alpha/beta ratio

## Alpha

- 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.

## Beta

- 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.

## Alpha/Beta

- Think about small alpha/beta ==> So beta should be big ==> that means repair capacity 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