- Mon Apr 17, 2023 7:49 am
I think “tattoos or tattooless” have nothing to do with correct breath hold level.
In our practice we use now SSN (reference level) for approximate initial verification to check that patient is in correct location in CC direction at the fixation, but only at the first fraction. Even more important for initial setup is that the patient is well fixed at the head cushion, relaxed and straight. Then we daily use planned couch value in AP direction, showing the correct spine location in AP. FB surface needs to be inside 1mm and 1° thresholds, also in AP direction. If the patient is 1 cm in incorrect LNG at the fixation (which we do not want her to be), it means only 1-2 mm displacement in AP for the spine if the tilt is 10° at the fixation. More effective seems to be to correct roll and arm position to reach FB VRT inside tolerances with planned couch VRT, typically there is needs to relax the patient at the setup. ROI mostly on the rigid surface seems useful. Then the switcing to BH surface ensures the correct BHL, which is as well visible on the patient monitor, the distance between FB and BH VRT should not vary daily, I mean that if the chest chould move 8 mm from FB to BH in VRT, it should move that much daily. With RPM we use daily the same couch VRT together with tattoos. RPM (and Catalyst) measures the baseline from the current chest posture. This seems to lead to good BHL as well (measured as the errors (AP) between spine and the sternum from LAT images). So I think, concerning BHL, to daily send to couch FB VRT with AlignRT may in most cases be adequate as well with not taking care of couch planned VRT. This is the practical workflow most uses, I suppose. We have however noticed it more accurate to use daily the same couch VRT and additionally to setup FB surface inside tight thresholds as well, to daily eliminate the possibilty to allow chest being differently relaxed (comparable to interfractional baseline drift) at the FB setup. The advantage of AlignRT is that already at setup we see that the patient is taking correct BHL from rotations- and LNG- and LATs parts as well, is in correct isocenter in BH as well. I do not see it important to daily check any SSDs or indexed values to show that the patient is in correct LNG in the fixation, since the reason may as well be that the posture of the patient is different not the LNG position of the patient, which one to correct? Sometimes I see that patient is asked to come caudally on the fixation to reach reference mark at sideindex and after this patient is not at the headrest anymore. This is what we should not do, since patient has for sure been well aligned at the headrest at the CT. I think AlignRT is more accurate to tell these and everything else we need to know. Some kind of daily images tell the rest.
Best regards rtt Marko