Brainstem Tolerance To Intensity-modulated Radiation Therapy Of Advanced T-stage Nasopharyngeal Carcinoma

OBJECTIVE: The aim of this study was to conduct an analysis of patients with advanced T-stage nasopharyngeal carcinoma and to document the incidence of brainstem toxicity after intensity-modulated radiation the-rapy (IMRT).METHODS: Forty-six patients with advanced T-stage nasopharyngeal carcinoma (NPC) underwent IMRT between 2007 and 2009. Dose-volume histograms were calculated for target and critical non-target structures. Radiotherapy was given once a day, 2.2 to 2.4 Gy per fraction, five fractions per week, with prescribed target doses ranging from 69.8 to 76.1 Gy (mean = 73.8 Gy). Limited doses to organs at risk were set according to the Radiation Therapy Oncology Group protocol (RTOG 0225), to protect normal tissues or minimize toxicity.RESULTS: Four (8.7%) patients developed brainstem toxicity. Increased risk of brainstem toxicity was significantly associated with maximum dose to the brainstem and V₅₀, V₅₅, V₆₀. Multivariate analysis identified an independent factor as an important prognosticator, i.e. V₆₀ (P = 0.00).CONCLUSION: The tolerance of the brainstem to IMRT is correlated to the volume included in high dose regions rather than the maximum dose of the brainstem alone. V₆₀ smaller than 1.90 cm³ appears to be clinically acceptable for patients with advanced T-stage NPC. Analysis of the exposed volume of brainstem tissue may be useful in IMRT planning for individual patients.