Potential retropharyngeal lymph node metastasis on diagnostic image and changes in retropharyngeal regional dose depending on the irradiation technique in maxillary sinus cancer

We retrospectively analyzed the frequency of retropharyngeal lymph node （Rp） metastasis on diagnostic images and the irradiation dose to the same area in 55 patients with advanced maxillary sinus squamous cell carcinoma who underwent external radiotherapy and superselective intra-arterial chemotherapy at Juntendo Hospital. Reassessment of pretreatment images revealed potential Rp metastases in 10 patients （18％）; 9 who were diagnosed with a minor axis of ≥ 5 mm and 1 diagnosed with a major axis of ≥ 10 mm. Patients who underwent MRI or PET-CT tended to have a high rate of Rp node metastases （P ＝ 0.090）. The median irradiation dose for Rp metastasis was 57.7 Gy, and 8/10 patients were irradiated with high doses without targeting. As a result, no recurrence of Rp metastasis was observed. When the Rp region is not targeted during intensity-modulated radiation therapy, the Rp region dose is significantly lower than that of three-dimensional radiation therapy （47.4 Gy vs. 36.0 Gy, respectively; p ＝ 0.040）.