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Discuss best practices and workflow advice for Surface Guided Radiation Therapy on all treatment sites.
By marko_laaksomaa Finland flag
Has anyone controlled secondary patient motion caused by 6D correction somehow in a daily practice? Have you taken new images after 2-3 degrees pitch and/or roll CBCT- corrections to verify that the patient has not shown sliding or spontaneous patient movement on the treatment couch due to large rotations performed? Have you utilized SGRT to show this possible error source, how exactly? Thank you! ... fb8f2e4c7e

Best regards Marko
By marko_laaksomaa Finland flag
May be some kind of solution is to acquire new “this session only” reference surface just before 6D couch shifts, then shift the couch and compare the AlignRT delta shifts with 6D couch corrections. Then we need to be aweke what is happening :geek: If those values agree with for example 2 mm and 1° accuracy, then the patient has not much moved during the 6D couch correction process. A limitation to reliably verify the succeeding of the 6D couch corrections with AlignRT is that the area of monitoring may shift in LNG for example that much that the external anatomy differs much of its original ROI location after the couch shifts. This is possible for example if the ROI is delineated too near stomach, too cranially, with the pelvis patient. In this kind of case, if the couch is shifted 1 cm in LNG based on CBCT match and AlignRT monitoring meets the stomach which has not been inside AlignRT ROI, at least pitch may differ dramatically between couch corrections and AlignRT. This means that in pelvis I think we should leave some kind of margin outside the fat tissue of stomach when delineating the pelvis ROI. With the phantoms this is not an issue, but with patients, with differing and deforming surface anatomy the situation is different. However, in several cases when the ROI locates in reliable rigid area, I could even rely on AlignRT when approximately verifying the succeeding of 6D couch corrections, to verify that the patient has not moved during or due to 6D couch correction in other words, which is the case of this topic right now. This is a great thing that SGRT with certain limitations can offer this possibility and may eliminate the need to acquire new CBCTs and thereby reduces the radiation dose, because re-imaging can be ignored. To discuss with the patient that the couch may move a lot before treatment, after imaging, may help a little, such that the patient does not get scared and for that reason move during the 6D couch corrections. Some may consider that this whole thing is not an issue at all and not worth to evaluate. What do you think?