Study of level Ib delineation, dose analysis and regional recurrence in level Ib lymph node-negative nasopharyngeal carcinoma patients treated by intensity-modulated radiotherapy

Abstract

Objective To investigate the level Ⅰb contouring, dose analysis and regional recurrence in level Ⅰb lymph node-negative (Ⅰb-negative) nasopharyngeal carcinoma (NPC) patients treated by intensity-modulated radiotherapy (IMRT). Methods One hundred ninety newly-diagnosed, Ⅰb-negative NPC patients treated by IMRT were enrolled. Level Ⅰb contouring and dose prescribing in this cohort were classified into planned prophylactic irradiation (PPI) group (56 cases) and non-planned prophylactic irradiation (non-PPI) group (134 cases). The mean dose (Dmean) of the level Ⅰb bilaterally and submandibular glands (SMGs) was recorded for comparison. Results After a median follow-up of 47 months, there was no level Ⅰb regional recurrences noted in the entire group. The mean doses of level Ⅰb and the submandibular glands were significantly lower in the non-PPI group than those in the PPI group as follows: (50.81±5.37) Gy vs (59.68±3.32) Gy for the left level Ⅰb, (51.55±5.02) Gy vs (59.66±3.85) Gy for the left submandibular gland, (51.55±5.02) Gy vs (59.66±3.85) Gy for the right level Ⅰb and (57.25±4.69) Gy vs (63.41±2.88) Gy for the right submandibular gland (all P=0.000). Conclusion In this retrospective analysis of non-randomized single institute data, it seems unlikely that PPI to level Ⅰb is necessary in Ⅰb-negative NPC patients treated by IMRT. Key words: Nasopharyngeal neoplasms; Intensity-modulated radiotherapy; Prophylactic irradiation