Long-term treatment outcome of nasopharyngeal carcinoma (NPC) using intensity-modulated radiotherapy (IMRT).

Abstract

5582 Background: A number of centers have reported promising early results of treating NPC patients using IMRT, in terms of locoregional control and parotid sparing. This study evaluated the sustainability of early favorable results, and late events. Methods: 231 consecutive NPC patients were treated with IMRT between 2000 and 2005. The proportion of stage I, IIA, IIB, III, IVA, and IVB disease was 8%, 5%, 14%, 32%, 28%, and 13% respectively. The prescribed dose was 66 Gy over 33 daily fractions to the gross tumor, 60 Gy to the planning target volume, and 54–60 Gy to the clinically negative neck. Majority of T1-2a patients received brachytherapy boost (12 Gy/ 4 fractions), and T2b-T4 patients received conformal or IMRT boost (6-8 Gy/ 3-4 fractions). Stage III–IVB patients also received concurrent chemotherapy, with or without neoadjuvant chemotherapy. Results: The median follow-up period was 59 months. The overall 6-year local failure-free survival (LFFS), regional failure-free survival (RFFS), distant metastasis-free survival (DMFS), and overall survival (OS) was 82%, 91%, 75%, and 66% respectively. Between 3 to 6 years there was a drop in LFFS, RFFS, and OS, while DMFS plateaued. Local failure was dominated by within-field failure (85%). 68% of local failure involved the skull base and intracranial region (rT3/4). Only two patients developed visual impairment despite a proportion of T3/4 patients had received > 54Gy to the optic nerves or chiasm. Radiation-induced malignancy occurred in 3 patients (2 in oral tongue, 1 in nasal cavity). The 5-year cumulative incidence of radiation-induced tongue cancer was 1.43%, higher than that seen after 2-dimensional radiotherapy. Conclusions: Although IMRT at a dose between 66-74 Gy achieves good early response and promising late toxicity profile, further locoregional recurrence can be seen on longer follow-up, especially at or above skull-base region. More vigorous use of adaptive and image-guidance radiotherapy may be needed to overcome potential setup error and volumetric changes during treatment course. The incidence of radiation-induced oral tongue cancer warrants further assessment. No significant financial relationships to disclose.