Usually all conventional radiotherapy LINAC have a collimator rotation, like varian elekta etc. But in the recent machines like Tomotherapy or VERO brain lab, the collimatort rotation is missing. So how practical is it to eleminate collimator rotation for 40 by 20 field collimator.
I think it is wise to remember that a Linac and Tomo are quite different beasts. Remember that tomo delivers a fan beam with a binary MLC in a helical fashio whilst a linac can at best deliver VMAT. Some other authors (just google the question) have shown that both IMRT and VMAT plans can be optimised with collimator rotation so if you wish to believe that then yes collimator rotation is still needed. Additionally you may not always going to treat everything with VMAT or IMRT so field shapes may be compromised without a collimator rotation. There is plenty of literature available on all these subjects.
Tomo and Vero are very different from LINAC I think in LINAC rotating collimator are compulsory whther in Tomo and Vero diue to field size is not necessary
In IMRT plans for each field we use the collimator rotation where MLCs move across PTV along its shortest extent. This often produces superior plans (better OAR sparing with the same PTV coverage) and often allow removal of the carriage move. The later normally results in less MUs required for the dose delivery.
On an IMRT with step and shoot collimator rotation adds an advantage but on a rapid arc or a vmat does they use collimator rotation?????
Yes an collimator rotation of non zero is important. First of all to spread out the inter leaf leakage, which for old MLC's can be 2-5%. For VMAT a non zero coll angle ads more degrees of freedom to the optimizer. From the MLC coordinate system each MLC work on different parts of the target during the rotation. Different optimizers work best around different angles. For SBRT lung Varian and Pinnacle work well between 15-35 degrees, where as Monaco prefer smaller coll rotations of 5 to 15 degrees.
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