ESTRO 2021 Abstract Book

S601

ESTRO 2021

exerted an independent role on EMOT, SOC or SYST acute deterioration (Table 2).

Conclusion Contrarily to that commonly believed, the acute PRO IT deriving from WPRT delivered with modern IMRT techniques is minimal. Interestingly, the WPRT-induced intestinal symptom most feared by the RO community, diarrhea, had an only negligible role in impairing the PRO QoL which was, quite unexpectedly, far more compromised by intestinal symptoms apparently only minimally affected by RT.

Poster discussions: Poster discussion 8: Head and Neck

PD-0770 Validation of USPIO-enhanced MRI to guide nodal irradiation in head and neck cancer patients D. Driessen 1 , T. Dijkema 1 , S. Pegge 2 , P. Zámecnik 2 , I. van Engen-van Grunsven 3 , W. Weijs 4 , R. Takes 5 , T. Scheenen 2 , H. Kaanders 1 1 Radboudumc, Radiation Oncology, Nijmegen, The Netherlands; 2 Radboudumc, Medical Imaging, Nijmegen, The Netherlands; 3 Radboudumc, Pathology, Nijmegen, The Netherlands; 4 Radboudumc, Oral- and Maxillofacial Surgery and Head and Neck Surgery, Nijmegen, The Netherlands; 5 Radboudumc, Otorhinolaryngology and Head and Neck Surgery, Nijmegen, The Netherlands Purpose or Objective At present, despite state-of-the-art staging, around 20% of head and neck cancer (HNC) patients with a clinically negative neck will have occult metastases. This is why the lymphatics are often treated electively and bilaterally to eradicate subclinical tumor deposits. More sensitive imaging methods are required to improve the nodal detection threshold. MRI with ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles used as contrast agent is a promising approach (figure 1). It has the potential to identify small nodal metastases and can guide radiation oncologists to safely tailor and de-escalate elective radiation volume and -dose. In this study we evaluate the accuracy of USPIO-MRI for the detection of nodal metastases in HNC.