2813 - Craniocaudal Spread Patterns of Retropharyngeal Lymph Node Metastasis in Patients with Oropharyngeal Carcinoma

10:45am - 12:00pm PT

Hall F

Screen: 30

POSTER

Presenter(s)

Mika Nakatake, MD - Nagasaki University, Nagasaki, Nagasaki

M. Nakatake¹, R. Toya¹, Y. Fukugawa², S. Shiraishi³, Y. Orita⁴, T. Hirai³, and N. Oya²; ¹Department of Radiological Sciences, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan, ²Department of Radiation Oncology, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan, ³Department of Diagnostic Radiology, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan, ⁴Department of Otolaryngology–Head and Neck Surgery, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan

Purpose/Objective(s): The widespread adoption of intensity-modulated radiotherapy (RT) has removed the need for an extended neck position during RT for head and neck cancers. Therefore, a treatment position that minimizes patient burden, such as that used for diagnostic imaging, is desirable. Currently, consensus guidelines published by Grégoire et al. in 2014 have been widely used for delineating neck node levels. However, no studies have comprehensively evaluated the spread patterns of retropharyngeal lymph node metastases (RPLNMs) in patients with oropharyngeal carcinoma (OPC). We determined the appropriate craniocaudal border of the retropharyngeal lymph nodes (RPLNs) in patients with OPC in order to recommend an optimized target volume for elective nodal irradiation (ENI).

Materials/Methods: Two board-certified radiation oncologists reviewed pretreatment FDG–PET/CT and contrast-enhanced thin-slice CT and MR images of 137 patients with OPC who underwent RT between 2011 and 2020. The radiological diagnostic criteria for RPLNM were a short-axis diameter =5 mm, necrosis, and/or abnormal FDG uptake. We assessed the distribution of RPLNMs and the position of the hyoid bone based on the vertebral body and disk level using images of the diagnostic (contrast-enhanced MR images) and RT (CT simulator images with neck extension) positions.

Results: Among the 137 patients with 274 sides, 37 patients with 43 sides developed RPLNM. The cranial border of RPLNMs was found above the hard palate on 5 (1.8%) and 3 (1.1%) sides, between the hard palate and cranial edge of the C1 body on 26 (9.5%) and 25 (9.1%) sides, at the C1 body on 10 (3.7%) and 12 (4.4%) sides, and at the C2 body on 2 (0.7%) and 3 (1.1%) sides in the diagnostic and RT positions, respectively. The caudal border of the RPLNMs was found between the hard palate and the caudal edge of the C2 body on 39 (14.3%) and 39 (14.3%) sides, at the C2/3 level on 2 (0.7%) and 2 (0.7%) sides, the C3 body on 1 (0.4%) and 1 (0.4%) sides, and at the C3/4 level on 1 (0.4%) and 1 (0.4%) sides in the diagnostic and RT positions, respectively. Among the 37 patients with RPLNM, the caudal edge of the hyoid bone body was most commonly located at the level of the C5 body in 13 (35.1%) patients, followed by the C4 body in 12 (32.4%) patients in the diagnostic position. In the RT position, the caudal edge of the hyoid bone body was most commonly located at the level of the C3 body in 16 (43.2%) patients, followed by the C4 body in 11 (29.7%) patients.

Conclusion: Patients with OPC rarely present with RPLNMs above the hard palate and below the C2/3 level. The cranial edge level of the hyoid bone varied significantly among the treatment positions. The craniocaudal borders of the RPLNs for ENI should be defined as the hard palate and cranial edge of C3.