Ming-Hsiang Liou, Tsair-Fwu Lee, Shyh-An Yeh, Pei-Ju Chao, Hui-Min Ting, Yu-Jie Huang, Hsiao-Yi Lee
Division of Radiation Oncology, Yuan's General Hospital, Taiwan
Purpose: To determine the best-fit parameters for the logistic and the Lyman-Kutcher-Burman (LKB) normal tissue complication probability (NTCP) models for optimizing cochlea constraints to avoid causing tinnitus after head-and-neck cancer (HNC) intensity-modulated radiation therapy (IMRT).
Methods and Materials: A total of 422 ears from 211 patients with HNC were included in the study. The analytical endpoint was defined as grade 2+ tinnitus that occurred within 1 year of IMRT. The logistic and LΚΒ NTCP models were used to assess the incidence of grade 2+ tinnitus. The best-fit values for TD50 were determined using maximumlikelihood estimates. A guideline of TD25 is recommended for the tolerance dose to produce a 25% complication rate within a specific period of time.
Results: Forty-five of the four hundred and twenty-two samples (10.7%) developed grade 2+ tinnitus symptoms after IMRT, as diagnosed by a clinician. The NTCP-fitted parameters were TD50 = 37.35 Gy (CI, 36.50-38.20), Γ50 = 1.60 (CI, 1.58-1.62), and TD50 = 35.92 Gy (CI, 35.07-36.77), m = 0.20 (CI, 0.18-0.22) for the logistic and LKB models, respectively.
Conclusion: To maintain the incidence of grade 2+ tinnitus toxicity <20%, we suggest that the mean dose to the cochlea should be <29 Gy.
Keywords: Tinnitus, NTCP, cochlea, head and neck, constraints.