Bob,
You pose some very interesting questions in terms of the evolution of the GK and LINAC machines. Candidly, in terms of how many of what type of system or machine are out there, I'm not sure , but I'm also not clear how relevant that is to a treatment choice. Having been in the hospital supply business my entire business career I can say confidently that decisions on what machines to purchase by a hospital don't always reflect a "best of breed" criteria. For example, GK like many medical device manufacturers , has established many financially supportive relationships with key medical centers that purchased it's machines such as Pitt and UVA which influences what they buy and recommend to patients. Others that can't afford a dedicated GK machine, get one that can do IMRT but be utilized for radiosurgery when necessary by means of a headframe or other restraint such as Novalis. Politics, backside money, mutiliplicity of functionality with limited capital dollars all impact big capital purchases of CK, GK and others. It is what it is, but the machines are what they are.
LINAC machines arose in the 80's as an alternative to the cobalt radioactive source of GK. The biological impact to the AN is the same, the difference is that the cobalt is "dirtier" to dispose of then the radiation generated by the linear accelerator which does not have the disposal issue. There is no differential to the patient or AN
You're absolutely right that there are a variety of FSR protocols both in terms of total GY delivered and number of days to deliver it. It is clearly variable to the individual preferences of the physician as well as the unique aspects of the tumor as they program it into the computer. In the CK environment , while the majority of the practioners seem to use the 3 day approach such as I had, I have also seen folks that had 1 or 5. Is one better than the other or is that there that much difference in outcome in any of them is a great question which I think is best answered by asking how long have they done the protocol and what do their outcomes show over what period of time. Additionally, the number of treatments is often dictated by the machines ability. GK and CK are the most accurate and can deliver higher doses in less treatments safely. Other machines such as Novalis are not as accuarate and will usually have a larger number of treatments at a lower dose to compensate. In other words, knowing they will have more "collateral" damage than the other machines , they spread the treatments over more days
I don't know if the above gets at all of your questions , but hopefully it addresses some
mark
