Optimization study of postoperative radiotherapy plans for parotid cancer based on cochlea protection
Objective To optimize the radiotherapy plan after parotid cancer surgery based on reducing the cochlear dose,so as to achieve the optimal protection of the cochlea.Methods The data of 20 patients who had completed postoperative radiotherapy for parotid cancer in Guangdong Provincial Peoples Hospital Affiliated to Southern Medical University from January 1,2020 to December 30,2023 were retrospectively collected,and the radiotherapy plan of these patients was re-designed.In the new plan,the use of volumetric arc intensity modulated radiation therapy(VMAT)technology requires that the average dose received by the ipsilateral cochlea should be as low as possible,while the target dose requirements remain unchanged.The conformity and uniformity of the target area,as well as the dose to the cochlea and other organs at risk,were analyzed and compared between the original VMAT(VMAT_o)and optimized VMAT(VMAT_n)plans.The probability of radiation-induced ear injury was predicted by using the Normal Tissue Complication Probability(NT-CP)model.Paired t-test or nonparametric paired Wilcoxon test were used to compare the dose to organs at risk and target dose differences between VMAT_o and VMAT_n plans.Results Compared with VMAT_o plan,VMAT_n plan reduced the average cochlear dose from 36.43(17.24,39.12)Gy to 8.12(6.85,9.76)Gy(Z=-3.920,P＜0.001).The conformity and u-niformity of the target area and the dose of other organs at risk were not affected.According to the prediction of NTCP model,the probability of ipsilateral tinnitus decreased from 26.78％(3.77％,32.50％)to 0.92％(0.74％,1.20％)under the VMAT_n plan(Z=-3.920,P＜0.001),and the probability of hearing loss also decreased from 1.75％(0.00％,4.15％)to 0.00％(0.00％,0.00％)under the VMAT_n plan(Z=-3.920,P＜0.001).Conclusions Through the optimization of radio-therapy plan based on cochlear protection,the dose to the cochlea can be significantly reduced without affecting the target radiation dose.Therefore,the probability of tinnitus and hearing loss caused by radiotherapy can be significantly reduced.
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