ESTRO 2021 Abstract Book

S602

ESTRO 2021

Materials and Methods In this ongoing prospective study, 25 cT0-4N0-3M0 HNC patients scheduled for a neck dissection will be included. The data of the first 10 patients will be used to define which characteristics on USPIO-MR images represent metastatic and non-metastatic lymph nodes to develop a scoring system (phase I). The data of the next 15 patients will be used for validation (phase II). Prior to surgery, USPIO is intravenously administered and 24-36 hours later an in vivo MRI-scan is performed. After surgery, an ex vivo MRI of the neck dissection specimen is acquired. Suspicious nodes on in vivo USPIO-MRI are identified by two radiologists and correlated to the ex vivo MRI. The ex vivo MRI is present at the dissection room and guides the pathologist to localize the suspicious nodes to enable a node-to-node correlation between MRI and histopathology. Histopathologic results serve as the reference standard to validate the USPIO-MR results. Results Accrual of 10 patients for phase I of the study is completed. Our preliminary results show that during routine diagnostic work-up, 7 pathologic nodes (median size 20 mm) were found. On in vivo USPIO-MRI, 13 pathologic nodes (median size 7.5 mm) were identified and could all be matched to the surgical resection specimen. Histopathologic analysis revealed 12 additional metastatic nodes, i.e. total 25. The median size of the 6 metastases identified on USPIO-MRI but missed with routine imaging was 5.6 mm. USPIO-MRI identified at least one lymph node metastasis in all 6 lymph node positive patients (100%) whereas routine imaging identified at least one lymph node metastasis in only 3 of the 6 patients (50%). The remaining 4 lymph node negative patients were all (100%) correctly identified by routine imaging. USPIO-MRI, however, identified 3 of the 4 falsely positive. Conclusion USPIO-MRI is feasible in HNC patients, has a lower detection threshold when compared to routine diagnostics and correctly identifies all lymph node positive patients. Characterization of positive and negative lymph nodes on USPIO-MRI is currently in progress to particularly reduce the number of false positive results. PD-0771 Correlation of cfDNA with response in carcinoma of head and neck treated with chemoradiotherapy S. Parida 1 , M. Rastogi 1 , A.K. Gandhi 1 , S. Sapru 1 , N. Husain 2 , R. Khurana 1 , R. Hadi 1 , S.P. Mishra 1 , A. Srivastava 1 , A. Bharati 1 , S. Srivastava 1 1 Dr Ram Manohar Lohia Institute of Medical Sciences, Radiation Oncology, Lucknow, India; 2 Dr Ram Manohar Lohia Institute of Medical Sciences, Pathology, Lucknow, India Purpose or Objective Treatment response assessment in locally advanced head and neck squamous cell carcinomas (LAHNSCC) treated with chemoradiotherapy is being done with conventional imaging and clinical examination. Changes in circulating free DNA (cfDNA) levels after treatment have been correlated with treatment response in various cancers. We aimed to correlate cfDNA levels with treatment response and to evaluate it as a potential biomarker in LAHNSCC.

Materials and Methods This was a prospective observational cohort study carried out on 34 LAHNSCC patients (stage III-IVA, AJCC 8 th