Certainly interesting and important question. Sometimes we have such belly breathing DIBH candidates at CT. We use RPM at the CT, marker box locates at the sternum (Improving the reproducibility of voluntary deep inspiration breath hold technique during adjuvant left-sided breast cancer radiotherapy. Skyttä et al.). Therapist try to coach the patient to rise the chest wall at least 6 mm in DIBH, BHL window is typically 3 mm, so the upper level of window is at the distance of 9 mm from the baseline minimum. If the patient cannot do that despite the rtts instructions to perform BH with thoracic breathing maneuver, typically with these patients FB is used and DIBH is excluded. The important knowledge from the literature is that abdomen DIBH saves the heart and patients benefit it if compared to FB (1. Abdominal DIBH reduces the cardiac dose even further: a prospective analysis. Zhao et al. 2. Comparison of thoracic and abdominal deep inspiration breath holds in whole-breast irradiation for patients with left-sided breast cancer. Hirata et al.). With Catalyst, in addition to SGRT features, user can use one or two trigger points to when necessary simultaneously control both chest and belly rise in VRT direction in DIBH, with defined thresholds. With AlignRT we have to choose either typical ROI for breast RT, which is in this kind of case not showing chest rise in BH, or bellyROI which is supposed to be unpractical and far away from the target, breast in this case. Some kind of combination of chest wall and belly with the ROI delineation MAY be used with these patients. It would be beneficial if with AlignRT we could have an option to chooce to simultaneously monitor two areas at the same time, perhaps both with beam control. The other additional area of interest could be only small point on the belly or wherever user wants to set it, demonstrating the breathing and BHL of that certain area. Finally, I am as well interested in to know how are other hospitals treating total belly breathers with AlignRT in BH, if they are.
Best regards Marko