Analysis Of Influencing Factors Of Hearing Impairment After Intensity Modulated Radiotherapy For Nasopharyngeal Cancer

Object:Discover the effect that influencing factors have on hearing in nasopharyngeal carcinoma patients after intensity modulated radiation therapy,and to provide assistance for making radiotherapy plans.Method: We selected 75 cases of patients of pathologically confirmed nasopharyngeal cancer who had taken their first intensity modulated radiotherapy in department of radiotherapy in the fourth hospital of hebei medical university from Jan 2005 to Dec 2009. Subsequently,we drew the ear structure from plan system,read the corresponding volume dose from plan system,mean dose,and maximum dose,and deduced the correlation of the data with hearing impairment using the software"SPSS13.0". Theχ~2 test was used for the comparison of the measured data,and P<0.05 was considered statistically significant.Results: The T stage(P=0.023) , history of otitis media before radiotherapy (P=0.023) and nasopharyngeal cancer's invasion into lateral wall (P=0.033) shows significant correlation with hearing impairment after radiotherapy. Possible impact of radiation dose on hearing : middle ear:(1) Middle ear average dose>45Gy(P=0.035),middle ear V30>75%,(P=0.043),middle ear V50>65%(P=0.048),have a statistically significant different incidence of developing hearing impairment;and middle ear average>50Gy,have a statistically significant different incidence of developing Grade II hearing impairment(P=0.019).(2)External ear maximum dose>45Gy (P=0.036),have a statistically significant different incidence of developing hearing impairment.;external ear maximum>60Gy(P=0.021),external ear V10>80%(P=0.003),external ear V20>60%(P=0.003) have a statistically significant different incidence of developing Grade II hearing impairment.Conclusion: The appropriate ear dose range is: the middle ear average≤ 45Gy,the middle ear V30≤75%,middle ear V50≤65%,and external ear maximum≤45Gy. The appropriate ear dose range to avoid Grade II ear hearing loss after intensity modulated radiotherapy for nasopharyngeal cancer is: the middle ear average≤50Gy,external earV10≤80%,external earV20≤60%,the external ear maximum≤60Gy.For the patients who have history of otitis media before radiotherapy should low the dose.