Attendee Question from 9th International Novalis Circle Congress.
Section: Physics Elements - Treatment Time Effects and BED
Speaker: Matt Skinner
Do you consider that the dose to each voxel should be corrected by time and dose rate? The dose delivered to each voxel in a VMAT treatment is time dependent.
Comments
M
Hopewell's 2013 article on VS with Gamma Knife did this. They looked voxel-by-voxel and produced iso BED distribution instead of isodose and you can see the difference between the two. Ideally, yes, the dose delivered to each voxel does vary by time throughout the treatment however VMAT delivery in VS is different than Gamma Knife where individual isocenters are delivered sequentially so one aspect of the tumor may not receive appreciable dose until later (or earlier) in the delivery - or it receives part early on and the other part much later. In VMAT, each arc does provide, generally speaking, more irradiation of the entire target volume, so dose builds up across the target. In our study we also found that the treatment times were far shorter on the linac - mean time was 8.3 minutes for a typical 4 arc plan, with a range of 4 to 18 minutes. All but one plan was delivered in under 14 minutes.