| Objective: Radiation therapy of nasopharyngeal carcinoma may lead to high frequency radiation damage of cochlea,which results in sensorineural hearing loss in high frequency band.Controversy still exists about the dose volume tolerance of cochlea in the era of intensity-modulated radiation therapy.Through the analysis of the inner ear cochlear volume dosimetry limited intensity-modulated radiotherapy for nasopharyngeal carcinoma,to investigate the cochlear target delineation method,collect basic data of normal cochlear volume,analysis the actually received dose of cochlea in each stage and its influence factors。so that we can lay a foundation for the research on dose volume tolerance of cochlea for the next step of the actual explorationMethod: Retrospective statistics 202 cases with nasopharyngeal carcinoma from January 2009 to March 2016 in the First Affiliated Hospital of Fujian Medical University IMRT cases,all patients with IMRT plans have been set up inner dose volume limit（V50≤50%）.First,delineating cochlea in the treatment planning system（TPS）,recalculating the dose of cochlea,collecting the date of average volume、average dose(Dmean)、close to the maximum dose（D2%）of the bilateral cochlea.Then calculating the mean cochlear size and different clinical stages（T,N,TNM）cochlea the accepted dose of Dmean and D2%,analysis of the factors affecting the cochlear dose.Using SPSS 24 software for data processing and statistical analysis.Results: 1)The actual prescription dose of D95% PTVnx on nasopharyngeal in T1、T2、T3、T4:61.727 Gy + 12.50,62.890 + 18.02 Gy,62.620 Gy,61.985 + 15.57 Gy + 27.78,D95% showed no significant dose differences of different stages of T（P=0.920 > 0.05）.2)The average number of bilateral cochlear volume（Vmean）was 0.142cm3 + 0.022,the average volume of left and right cochlea（VL,VR）were 0.143 cm3 + 0.024,0.142 cm3 + 0.024,the median were 0.140 cm3,0.140 cm3,VL and VR no significant difference （χ2=0.010,P=0.920）;the difference between men and women VL,VR and Vmean there was no statistical significance（χ2=0.001,P=0.970;χ2=0.801,P=0.371;χ2=0.019,P=0.889）.3)Bilateral cochlear Dmean mean of 5095.8 + 948.2,which left Dmean for 5179.5c Gy + 1106.5,median 5034 c Gy,maximum 7528 c Gy and minimum 2574 c Gy;the right side is 5012.0c Gy + 1034.6,median 4895 c Gy,maximum 7512 c Gy,minimum 2445 c Gy;bilateral cochlear D2% mean 5854.0c Gy + 892,which left D2% for 5935.4c Gy.1008.8,median 5824.5c Gy,maximum 7908 c Gy and minimum 3085 c Gy;the right side is 5772.4c Gy + 1025.4,median 5720 c Gy,maximum 7994 c Gy,minimum 1890 c Gy.4)T1,T2,T3,T4,the average dose of Dmean-L left cochlea were 44.686 Gy and 46.434 Gy + 10.382 + 8.329,50.318 + 9.379,60.629 + Gy Gy 9.695,D2%-L were 51.610 Gy and 54.544 Gy + 937.1 + 7.577,57.949 + 8.690 Gy,67.851 Gy + 7.925;right cochlea Dmean-R = 43.398 Gy + 8.307,44.728 + 7.710 Gy,49.450 Gy,57.917 + 8.811 Gy + 988.1,D2%-R was 5105.2 Gy + 821.7,5239.9 + 741.6 Gy,5726.1 Gy,6520.9 Gy + 890.7 + 978.7.5)Effects of bilateral cochlear dose(Dmean-L,Dmean-R,D2%-L,D2%-R)of the single factor analysis showed that T stage and TNM stage were significant influencing factors;logistic regression analysis showed that only T staging for bilateral cochlear dose(Dmean-L,Dmean-R,D2%-L,D2%-R the independent impact factor).Conclusion: 1)The volume of normal cochlea and cochlea is about 0.142cm3 + 0.022,the volume of cochlea is similar in male and female,but the difference is not statistically significant.2)The mean Dmean and D2% of bilateral cochlea were 50.958Gy+ 9.482 and 58.540 Gy + 8.92.Within the limits of the inner ear,the actual dose of cochlea,Dmean and D2% remain high,the incidence of SNHL may be high.3)With the increase of T staging and TNM staging,the actual amount of Dmean and D2% in cochlea is larger,suggesting that the nasopharyngeal carcinoma patients with T stage should pay attention to the protection of cochlea,so as to minimize the incidence of sensorineural hearing loss. |
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