HI,
1.I read about stereo tactic radio surgery physics , but i don't understand what is the important different between external beam radio therapy and srs.
except the stereo tactic techniques which is required for fixing skull and narrowing beam which aided to intracranial target volume?
I have many question for example:
I don't know how we can flat this narrow beam in different arc? it is the same procedures which is done in external therapy by filter?
2. In the gamma knife system we need to how many source ? the number of ports is equal the number of source?or more?
Thanks in advance.
A first answer.
The nr of sources in Gammaknife is identical to the nr of ports. The number is 201 co-60 sources of about 12 GBq Co-60.
And if you overlap so many beam profiles a gaussian dose distribution works as well as "flat" profiles.
Trying to add value to Hanno's answer, a major difference between stereotactic radiosurgery (SRS) and external bean radiation therapy (EBRT) is the dose delivered in the number of fractions. SRS delivers what will results as an ablative dose (e.g. 15-20Gy) in generally a single fraction whilst EBRT may deliver 40-80Gy over 16-20-35 fractions. Radiologically the SRS delivers a dose equivalent to something around 100-120Gy in a 2Gy fractionated approach all over a 1hour single visit session.
SRS is also generally employed on small lesions up to about 0.3cm-3cm max diameter (dose is adjusted according to size) rather than e.g. EBRT for a lung lesions ~8cm sphere.
The 201 beams from the 201 Co-60 sources (although I believe now the number of sources have been reduced in the new Elekta Pefextion) can be collimated in size or "switched" off. The old gamma knife had a collimator piece that had to be loaded into the machine after each port was appropriately loaded, I have attached a few photos of got back in 94 of a unit in the UK. The newer gamma knife does the collimation internally.
Thanks so much
although i read some books but i don't have visual concept of srs and there are some unclear point in my mind.
since i should present this subject 7 days later i fear about questions which will have been asked from me !.
thanks again for your answers and photos.
To give you a further impression I add a chapter of one of my textbooks. It´s written in german, but the figures are easily understandable.
Good succes with your presentation. You may use my figures.
Thanks a lot for your help.
your file is use full.
it is my pleasure, i will use from them.(with permition).
HI Mr. Nazmabadi
many thanks for your answers
ensha'allah , I tend to optimization in IMRT.
Hope you are success in your life as in your job.
Thanks again.
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