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

Marko Laaksomaa

Hi all
…With current workflow, where patients arms now are set relaxed on the sides, clavicular displacement errors after daily IGRT (online match typically performed based on c3) in LNG direction are smaller in comparison to previous data with AlignRT. As well we begin to learn how to use postural setup etc. 6 mm or larger clavicular displacement exists now in 21% of the offline matched cases (offline matched claviculas n=180 in new data). The random error is 4.3 mm and no difference between 5 point open mask and AlignRT open mask group exist anymore (p=0.41). All the patients still have outliers concerning shoulder reproducibility and still even 2 cm clavicular displacements were noticed in latest data too. This is typical with 5- point masks as well and shifts can occur equally both early and late in treatment. (Neubauer et al. Assessment of shoulder position variation and its impact on IMRT and VMAT doses for head and neck cancer). Weight loss and thereby changed body contour for example is well controlled with new reference surfaces with AlignRT in comparison to 5- point masks without SGRT, in the cases when treatment is allowed to continue without re- planning. I have never offline matched claviculas before this study and it was a surprise how much claviculas can have displacement inside 5 point masks. At the same time with clavicular matches (reported here), I have done comparison of residual errors to c1, c5/7, mandible and base of the skull between the Groups (AlignRT+ 3 point open mask+ daily IGRT) and (laser setup+ 5-point mask+ daily IGRT). No difference in the residual errors or errors between the structures exist between the groups so far. Calculated residual margins in the named locations are 5 mm or below with daily IGRT. Methods to offline evaluate the images are taken from paper published over 10 years ago, but which is still relevant to demonstrate the complexity to treat accurately the large neck PTV (van Kranen et al. Setup Uncertainties of Anatomical Sub-Regions in Head-and-Neck Cancer Patients After Offline CBCT Guidance). It has also been reported that when we reduce the mask material (from 5- point mask to 3 point mask for example), patient is feeling less anxiety (Sharp et al. Randomized trial on two types of thermoplastic masks for patient immobilization during radiation therapy for head-and-neck cancer). This is our goal as well with SGRT and with open masks. With AlignRT faceROI in SRS treatments good setup results for the skull are found in comparison to CBCT 6D data, which was considered as a reference (Lee et al. Accuracy of surface-guided patient setup for conventional radiotherapy of brain and nasopharnx cancer). If in addition to this patient keeps the mouth closed similarly at the CT and at the linac, faceROI should be a good starting point to reach good accuracy in the mandible and in the base of the skull, which are important landmarks in the neck RT. Now it seems that this AlignRT head and neck setup workflow which was presented in the SGRT community first by M. Tallhamer, seems to work well with small additional adjustments. Lastly, it seems that taking the new SGRT surface for the setup is often necessary (after perfect images) if we want to see and setup the straightness of the patient with postural setup, since DICOM typically ends too cranially. Lets hope that we can keep the same good course as we have at the moment with AlignRT neck RT and slightly improve the shoulder reproducibility. I will let you know again at some point. All the best!

Best regards Marko