Dose Constraints Of Optic Oerves And Chiasm In Locally Advanced Nasopharyngeal Carcinoma Patients Treated With Intensity-Modulated Radiotherapy

Objective:This study evaluates the radiation induced optic neuropathy (RION) in nasopharyngeal carcinoma (NPC) patients of which the dose to 2% of the volume (D2) for the optic nerves and/or chiasm exceed 55Gy undergoing intensity-modulated radiotherapy (IMRT), and assess the optic nerves and chiasm tolerance dose.Methods:The clinical and dosimetric characteristics in 108 NPC patients treated with IMRT between May 2009 and December 2013 were retrospectively reviewed. The Common Terminology Criteria for Adverse Events (CTCAE) Version 3.0 grading criteria for visual impairment were utilized. Logistic regression analyses were performed to assess patient-and treatment-related factors on the development of RION. Survival estimates were determined by the Kaplan-Meier method.Results:No patient had severe RION (Grade 3-5) diagnosed, although 7 of 108 patients had slight (Grade 1-2) optic nerve disorder. No variables were foundto correlate with thiscomplication(P>0.05). For 193 optic nerves of 103 patients, the median Drriax was 68.59Gy (range,58.34-76.18Gy), the median D2 was 64.26Gy (range,55.14-74.04Gy), the median D5 was 62.15Gy (range, 53.72-73.15Gy), the median D30 was 53.12Gy (range,47.31-70.49Gy) and the median Dm was 45.02Gy (range,39.22-67.76Gy). For chiasms of 105 patients, these numbers were-Dmax:median 70.75Gy (range 57.49-74.85Gy), D2: median 67.02Gy (range 55.16-73.05Gy), D5:median 65.28Gy (range 52.59-72.39Gy), D30:median 58.52Gy (range 39.05-70.04Gy), and Dm: median 55.49Gy (range 29.33-69.76Gy). With a median follow-up of 32 months (range,13-77 months), the 3-year estimated OS, LRFS and DMFS were 90.0%,94.5% and 86.4%, respectively.Conclusion:Our study suggests that for optic nerves and chiasm the dose constraint<55Gy derived from conventional radiotherapy seems not applied to IMRT. Furthermore, the generally accepted optic nerves and chiasm dose constraints might be appropriately relaxed in order to improve target coverage, with promising initial results among advanced NPC patients treated with IMRT.