Forums SGRT – Best Practice Head and neck setup Reply To: Head and neck setup


Marko Laaksomaa
Participant

So, I matched offline some claviculas in the setup images in Group L (laser) with 5- point closed mask and in Group A (AlignRT) with 3 point open mask, one clavicula at the time. Workflow is outlined earlier in the text. Offline matching was performed to the claviculas point, which located 9 cm laterally from the bony vertebral midline in AP- kV- image. In total, 232 clavicula-match was performed in A and 528 matches in L. The combined (left + right clavicula) results demonstrate the residual errors of the clavicula after daily IGRT. If the re-setup was performed in either group due to displacement of the claviculas, the images before re-setup were included in the study. Thus, the results better demonstrate the real reproducibility of the setup itself. In the named point, residual error of the clavicula exceeded 6 mm in the setup images in the LNG in 23% (L) and 35% (A) of the fractions. The random error was smaller in group L than in Group A (3.8 mm vs. 5.7 mm p= 0.01). Margin needed in that point of clavicula, with daily IGRT, calculated with VanHerk formula was 1.1 cm in both groups.
I think that in the cases where raw systematic displacement of the clavicula exists, with SGRT it is easier to reduce this error with new reference surfaces. If systematic clavicular displacement error exists in Group L, it is in theory more difficult to approximate the new correct location of the shoulders inside the 5-point mask and reproduce this at the setup daily. The number of patients is still too small, but the beginning demonstrates that with postural setup, we need more practice to setup shoulders accurately. Otherwise AlignRT with neck patients seems promising. Lastly, on the first phase of the study patients had ring on their hands to hold. In these results given above, most of the patients had this ring. We considered not to use that ring now, instead arms now lay relaxed on the side. It seems to be easier to setup such arms/shoulders with postural setup. I know, that we will get this shoulder reproducibility with AlignRT to acceptable level soon, but this text could be a word of caution, change to SGRT in neck will not necessarily happen completely without challenges.
The ones that are using postural setup to setup shoulders in neck RT, please could you give some tips here or with e- mail marko.laaksomaa@pshp.fi. Thank you.