Hi Steven
I begin with saying, yes, in stereotactic treatments we often need intrafractional imaging. SGRT alone can not see inside the body.
We have simultaneous SGRT+triggered imaging in use only in SBRT prostate. The beam is hold only based on triggered imaging and AlignRT is used for the setup and without beam control during treatment. As mentioned in the study,
https://aapm.onlinelibrary.wiley.com/do ... acm2.13740, even though most of the treatments of the patients went well with this combination (SGRT+triggered imaginf), there was some false beam interruptions due to mentioned blocking of the cameras by the imaging arms. For this reason, some hospitals use AlignRT without beam control in SBRT cases with triggered imaging and manually stop the beam if deltas clearly go out of tolerances, but not due to blinking. With some factors, such as correct ROI delineation, we can affect how to operate optimal with the existing systems. Ok, this was my answer. Then some consideration around this topic.
To me this all present oneself as an area of improvement. Varian has not lately brought any pivotal solutions for reliable intrafractional imaging. In addition, triggered imaging goes 90° in different angle than the beam. On the other hand, it seems like VisionRT needs some small improvements for this mentioned issue; to improve beam not to be hold at any time for the reason that imagers or gantry block the cameras.
The simultaneous real time monitoring with SGRT+ intrafractional imaging, both interrupting (automatically and reliably) the beam based on 6D reference (VRT,LNG,LAT, ROT, ROLL, PITCH) only if patient/target has moved is a good goal for collaboration of Varian+VisionRT.
These two things mentioned above, challenging mostly Varian of course, may lead hospitals to consider to purchase expensive ExacTrac for SBRT/SRS, which offers both SGRT+intrafractional imaging both with automatic beam control in 6D (imaging based on markers and/or bones), even though the ExacTrac SGRT itself is based on one camera system with its own possible challenges again. However, in stereotactic treatments (as seen in this forum several times) in some/most cases we want those both to be used, SGRT for real time monitoring and more reliable imaging during treatment. Further, faster intrafractional correction tool (CBCT) than Varian can nowadays offer is needed. On the other hand, it is not yet possible to shift the couch to correct location based on match to lung tumor with ExacTracs images either, however they are working with that important item.
Please, give more practical answer to Steven and challenge my thoughts.
Marko