Abstract
Objective To investigate the protective effects of reducing average radiation dose and increasing protective weight on the auditory system (tympanic cavity,the bony portion of eustachian tube,vestibule,and cochlea) during intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC).Methods The planning system (ADAC Pinnacle3 8.0m) with direct machine parameter optimization was used to optimize the IMRT planning for 40 patients with NPC (stage Ⅰ + Ⅱ:20 patients ;stage Ⅲ + Ⅳ:20 patients).Without reducing the radiation dose for target volume,the IMRT planning was optimized by limiting the average dose administered to the auditory system or increasing the protective weight for the protected organs in auditory system.The protective effects were assessed by analyzing the average dose received by the auditory system.Results After limiting the average dose administered to the auditory system without reducing the radiation dose for target volume,the average dose received by the auditory system was significantly reduced (3855.5-5391.3 Gy vs 2960.3-4559.6 Gy,P =0.000 for all) ; when the protective weight for the auditory system was increased,the average dose received by the auditory system was even more reduced (3855.5-5391.3 Gy vs 2725.4-4271.4 Gy,P =0.000 for all).For all three regimens,the average dose was significantly higher in stage Ⅲ + Ⅳ patients than in stage Ⅰ + Ⅱ patients (P =0.000 for all).Conclusions For the IMRT planning for NPC,limiting the average dose administered to the auditory system can greatly reduce the average dose received by the auditory system,and increasing the protective weight for the auditory system can further reduce the average dose received by the auditory system.However,the protective effect on the auditory system may be reduced as the stage of NPC increases. Key words: Auditory organ; Dose limitation; Optimized weight; Nasopharyngeal neoplasms/intensity-modulated radiotherapy
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