A Clinical Investigation Of Protecting Auditory Function By Mri-guiding Intensity Modulated Radiation Therapy During Treatment Of Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma(NPC) is the malignant tumor with the highest rates of incidence in China. Radiotherapy is actually the best frontline treatment. The tumor size and involved sites of patients are different, however, auditory organs of the middle ear and the inner ear are usually located around the tumor target. When patients are treated by radiation, their auditory organs are risking heavy dose of radiation during intensity modulated radiation therapy(IMRT), therefore, irreversible hearing impairment will be caused. Under the condition of modern radiotherapy techniques, the 5-year survival rate of NPC has reached 80-90%. One of the hot points in recent research is how to improve the survival qualities of patients. This study investigated the effects of accurate target delineation after image fusion of MRI and CT during intensity modulated radiation therapy(IMRT) of nasopharyngeal carcinoma, to protect auditory organs.The T1-weighted and T2-weighted MRI images and CT images were scanned in 17 patients. After CT-MRI image fusion, the values of tumor target volume for CT images and fused images were both achieved. Based on statistical analysis, the values of tumor target volume are larger on CT images then on fused images. The delineation of the gross tumor volume(GTV) and middle ear organs is more effective on CT image, meanwhile the effect of delineation of inner ear organs is better on T2-weighted MRI images.This study investigated the effects of dose limitation and improved protective weighting on auditory organ dose distribution during IMRT of nasopharyngeal carcinoma, without reducing tumor dose. Results indicated that limiting the average dose administered to the auditory system, and further more promoting the protection weighting of the auditory system, the average dose administered to the auditory system was greatly reduced.Vestibulocochlear nerve was reconstructed through diffusion tenser imaging-based fiber tracking. The extracted vestibulocochlear nerve was finally mapped to CT image. Results suggested that limiting the average dose administered to the vestibulocochlear nerve reduced the averge dose received by the nerve.Our research demonstrated that, the accuracy of delineation of tumor targets and auditory organs could be greatly improved in CT-MRI fusion images. Reduction of the average dose administered to the auditory system along with protecting the vestibulocochlear nerve during IMRT, at the same time, the other normal organs at risk keeped in a limited dose as required. The incidence of hearing impairment could be reduced and the quality of life of patients could be further improved.