The Comparative Study On Intensity-modulated Radiotherapy For Nasopharyngeal Carcinoma:Different Target Volumes Definition And Different Target Dose Limited Methods Of The Cochlea And Innner Ear On The Protection Of Inner Ear Structure

Part one.Study of difference on inner ear organs sparing between QUANTEC cochlea and inner ear integral dose limited IMRT planning for nasopharyngeal carcinomaPurpose:To state the difference on inner ear organs sparing between QUANTEC cochlea and inner ear integral dose limited IMRT planning for nasopharyngeal carcinoma（NPC）,and to provide evidence for sparing of inner ear.Materials and Methods:20 patients with NPC(T_1-4)pathologically diagnosed were selected and inner ear,cochlea,vestibule and internal auditory canal（IAC）were contoured respectively on CT simulation image.Two sets IMRT plans was designed based QUANTEC cochlea（Dmean<4500cGy）and inner ear integral（Dmean<5000cGy）dose limited method respectively,and dosimetric difference were evaluated between them.Results:Volume of inner ear,cochlea,vestibule and IAC in 20 NPC cases is6.755cm³,0.256cm³,0.434cm³ and 0.686cm³ respectively.Dmean of cochlea based the cochlea and inner ear dose limited methods were 4658cGy and 4725cGy respectively,and those are all higher than level of 4500cGy,while Dmean of inner ear are all lower than level of 5000cGy（4658cGy and 4725cGy）.Dmax and Dmean of cochlea based QUANTEC cochlea planning are significantly lower than the inner ear planning（5569cGy Vs 5701cGy,P=0.020 and 4658cGy Vs 4725cGy,P=0.047cGy）,and Dmax of vestibular is also significantly reduced（5144cGy Vs 5178cGy,P=0.015）.While there is no dosimetric differences between the two plans in inner ear,IAC and Dmean of vestibule based.Conclusion:The QUANTEC cochlea dose limited method can improve the protection of the inner ear,at the same time simplify the outline of the inner ear,so it can replace method of inner ear integral dose limited for sparing the inner ear structures.Part two.The differences in normal tissue complication probability of innner ear and cochlea between target volumes recommended by Radiation Therapy Oncology Group and China in intensity-modulated radiotherapy for T_1-2 nasopharyngeal carcinomaPurpose: To evaluate the difference in normal tissue complication probability（NTCP）of inner ear and cochlea between target volumes recommended by China and Radiation Therapy Oncology Group（RTOG）in intensity-modulated radiotherapy for T_1-2 nasopharyngeal carcinoma,and to provide the basis of dose-volume effect for protection of inner ear and cochlea in intensity-modulated radiotherapy for nasopharyngeal carcinoma.Materials and Methods: A total of 20 patients with T_1-2 nasopharyngeal carcinoma were selected,and inner ear and cochlea were delineated on CT imagine.Target volumes delineation and treatment plan designing were performed according to the method recommended by RTOG0225（RTOG target volumes delineation method）and the Chinese Working Committee for Clinical Staging of nasopharyngeal carcinoma in 2010（Chinese target volumes delineation method）,and the differences were calculated in the dose to inner ear/ cochlea and NTCP.Results: In the RTOG and Chinese methods for target volumes delineation,Dmean to the left inner ear was（4489±440）c Gy/（4039±482）c Gy;to the right inner ear was（4339±749）c Gy/（3926±739）c Gy;to the left cochlea was（5109±396）c Gy /（4584±474）c Gy;to the right cochlea was（4855±774）c Gy/（4381±783）c Gy,respectively.In two methods for target volumes delineation,P to the left/right inner ear and the left/right cochlea were 0.000.In the RTOG and Chinese methods for target volumes delineation,Dmax to the left inner ear was（6369±355）c Gy/（5901±426）c Gy;to the right inner ear was（6247±463）c Gy /（5699±529）c Gy;to the left cochlea was（5794±354）c Gy /（5230±387）c Gy;to the right cochlea was（5616±562）c Gy / （5061±649）c Gy,respectively.In two methods for target volumes delineation,P to the left/right inner ear and the left/right cochlea were 0.000.In the RTOG and Chinese methods for target volumes delineation,NTCP to the left inner ear was 12（5.25²3.5）/ 3.5（2⁹.5）;to the right inner ear was 8（2.25¹9.75）/2.5（1⁸）;to the left cochlea was 23.5（16.25³5.75）/9（5.25¹6.75）;to the right cochlea was 14（6.25³3.75）/6（1.25¹2.5）,respectively.In two methods for target volumes delineation,P to the left/right inner ear and the left/right cochlea were 0.000、0.000、0.000、0.001.Conclusion: For T_1-2 nasopharyngeal carcinoma the NTCP of the inner ear is closely associated with target volume dose and irradiated volume,but the cochlea which has no obvious correlation with irradiated volume is related with irradiated dose.Of the two target volume delineation methods,the dose to the inner ear/cochlea and NTCP determined by the Chinese target volume delineation method are significantly lower than those determined by the RTOG method.