Should you change an ROI during a fraction due to camera blockage, without taking imaging to confirm alignment. Once you have an ROI specified and that is tied to an image alignment, i.e., captured after shifts are made from a cbct, does expanding or changing and ROI introducing an offset. Basically, how much can you change the ROI without re imaging, if any? With respect to different treatment site and techniques (3D, DIBH, SBRT, BH SBRT, etc. ), how big of a change is okay?
This is an interesting question. My standpoint is that radiographic imaging is the golden standard and SGRT is a strong and helpful add-on.
Before patient treatment, we check the ‘goodness’ of the ROI (includes as much topographic information as possible, includes isocenter if possible, includes lateral information). When considering how much lateral information to include, we consider the treatment technique and possible camera blockage. However, we do sometimes experience camera blockage during treatment. In such cases, we do not hesitate to edit a ROI during treatment for the sake of reducing camera blockage. The new ROI should of course still satisfy the above criteria. A different ROI, of course, contains slightly different patient alignment information. Following the above ‘rules’ for ROI drawing, the new ROI will carry much of the same information. If editing the ROI causes real-time-deltas to go out of tolerance, we reimage. If real-time-deltas are within tolerance, we continue the treatment without further ado.