Short- distance radiotherapy or brachytherapy:
The advantage: it gives a very large dose to the tumor with a minimum radiation to the surrounding normal tissue.
Disadvantage : The no uniformity of the dose and the radiation safety.
- The radiation source is radium but it replaced by 222Rn (radon gas) which is obtained by placing radium in a solution. Radon also by radioactive gold 198Au .There is also 125I which is used for permanent implants.
-Brachytherapy is also use beta particles ,fast electrons emitted certain radionucleus.
- The (Yttrium 90) 90Y is the most common source of beta particles ,it is continuously being formed by the decay of strontium 90Sr which emits beta ray with energy of 0.54 Mev and 90Y emits β-ray with energy of up to 2.22Mev ,these rays can penetrate about 4mm and almost ideal for treating lesions on the eye.
Electrons in radiotherapy :
- Electrons ,unlike gamma rays and x-rays ,have a fixed range.
- The radiation at low electron energies is relatively uniform over most of its travel and this advantage is gradually lost in going to higher electron energies .
- Disadvantage : there is some skin sparing since the maximum dose occur below the surface but its amount is small compared to that from high energy x-ray beams.
π-(Pi minus) mesons in radiotherapy:
- Disadvantage: there life time is 10-8sec, high cost ,and protection problems.
- Advantage: eliminate some or all of the oxygen effect