Gamma Radiation

The Difference Between Alpha, Beta and Gamma Radiation

Physical Origin

Gamma radiation, unlike alpha or beta, does not consist of any particles, instead, it is a photon of energy being emitted from an unstable nucleus.

Size, speed and range

Having no mass or charge, gamma radiation can travel through most forms of matter and further than alpha or beta radiation. Gamma rays travel at the speed of light and are used for External Beam Radiotherapy (EBRT) – the most common form of radiation therapy.
 

Gamma radiation is less targeted due to its long range and high penetration effect, increasing the risk that radiation will not only be deposited inside the tumor but will also harm the surrounding healthy tissue.

Image 9 - Gamma decay

Effect on cell

Gamma rays have a low LET and deposit less energy on targeted areas causing mainly single-stranded DNA breaks that are more easily repairable.[iv] As a result of gamma rays, much lower Relative Biological Effectiveness (RBE) compared to alpha radiation, higher doses are required to cause the equivalent biological damage, resulting in an increased risk of healthy tissues being destroyed in the crossfire.  


Furthermore, unlike alpha radiation, gamma radiation requires the presence of oxygen to create significant damage to the DNA - the so-called Oxygen Enhancement Ratio (OER) or oxygen enhancement effect. For solid tumors, where the inner parts are less oxygenated than normal tissue, an up to three times higher dose is needed to achieve the same therapeutic effect as in tissue with normal oxygenation. This use of increased dose brings with it increased risks of side effects from the long range of activity of gamma radiation.

 

 

 

Shielding

Thick, dense shielding is necessary to protect against gamma rays. To stop typical gamma rays by a factor of a billion, it would take 4.2 meters of water and 40 cm of lead! The higher the energy of the gamma ray, the thicker the shield must be.  

 

Why is alpha radiation better for cancer treatment?

 
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