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Thursday, 28/10/2021
Week 6, Lecture
Dr Azeem Saleem
Radiotherapy
What is radiotherapy?
Use of ionising radiation to treat disease
Treatment modality
Mainly used to treat cancer
50% of patients with cancer have radiotherapy
Can also be used for other diseases such as keloids and COVID
Radiation spectrum
Frequency increases towards the right
Electromagnetic spectrum has a wave
As the frequency gets higher the energy gets higher
Starts with ultraviolet and goes to where radiotherapy is
Start getting ionising radiation at this point
Ionising radiation
Any radiation over a certain frequency which can create ions
Water – any radiation can dislodge electrons from the water molecule and create an
electron
Bound together by chemical bonds so the radiation needs to be strong enough to
break the bonds
Carcinogenic in nature
Typically used for X-Rays and CT scans
Megavoltage radiation
Main sources are gamma rays and photons
Have no mass
Photoelectric effect versus Compton scattering
Megavoltage
o Compton scattering
o Produces ongoing cascade of electrons
o Independent of the atomic number
o No absorption of rays in the bone
o Radiation therapy – not absorbed in the bones so less side effects
Kilovoltage radiation
o x-rays
o photo-electric effect
o energy is deposited onto an atom
o depends on the atomic number – higher the number the more absorbed
o as bones have a high atomic number this is absorbed by the bones showing
the picture
Radiotherapy: Mechanism
When it ionises it creates free radicals
Very highly reactive
Creates DNA damage which results in damage to the radiated area
Both to normal tissue and the tumour
The aim is to damage the tumour
Oxygen very important for effectiveness
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