In the first three fractions we check from AP images that rotation of the vertebra (th1-th10) is inside 1 cm and the pitch/BHL measured from LAT image is in SI inside 7 mm and in AP inside 5 mm, this is measured from LAT image as the displacement errors between vertebra th6 and upper part of sternum. If these criterions are met, matching location is the compromise match between ribs and sternum in SI, ribs in the LAT direction, and sternum in the AP-direction. With this compromise match tangential image accuracy is with at least 90% effectiveness inside 5mm in SI and 4 mm in AP/LAT with AlignRT. Position of the shoulder joint should be inside 8 mm after compromise match, if not, either small (1-2 mm) shift in the matching location is done towards shoulder joint or arm re-setup is performed. If addition to these SI,LAT,AP isocenter in the orthogonal images are systematically inside 5 mm in the first three fraction, daily tangential AND weekly AP/LAT IGRT- protocol is performed. If the named threshold are exceeded in the three first fractions we continue with the orthogonal images as long as we have solved the problem. This mostly requires new VRT surfaces and changes in the original ROI.
If only AP/LAT images are acquired matching guidelines and protocols in the unit should be in good order to treat blindly the tangential. If only tangential images are acquired, one do not see enough about patient entire chest wall position. Both is better but unpractical. So we try in the first fractions make this AlignRT to discuss with the orthogonal images as reliably as possible and after that make IGRT protocoll lighter.
Best regards Marko