鼻咽癌放疗面颈联合颈后电子束野铅模制作问题的研究

目的探讨鼻咽癌放疗面颈联合颈后电子束野铅模制作问题。方法对5例不同等中心点深度的鼻咽癌面颈联合野放疗患者,按照分野前后的灯光野投影,在患者固定面罩上画出颈后电子束照射野。应用几何关系计算出所给定源片距的校正源片距,分别按照实际源片距和校正后源片距制作电子束铅模,到加速器下治疗摆位,测量源片距校正前后铅挡野与体表野的符合性。结果应用几何关系计算出所给定源片距的校正源片距,均大于给定源片距。源片距校正前的铅挡野与体表野偏差明显较大,最大偏差达1.25 cm;源片距校正后铅挡野与体表野偏差较小,最大偏差为0.22 cm。结论鼻咽癌面颈联合野后程分野颈后电子束野铅模制作时,应用首程等中心照射影像资料制作出来的铅模,偏差较大,通过源片距校正方法,铅挡野与体表照射野符合性较好。

Discussing Moulding Leaden Block in Posterior Neck Electron Beam Irradiation When Using Face-neck Field Irradiation for the Radiotherapy of Nasopharyngeal Carcinoma

Objective To discuss about moulding leaden block in posterior neck electron beam irradiation for the radiotherapy of nasopharyngeal carcinoma.Methods Five nasopharyngeal carcinoma patients with different depth of isocenter points were selected in this research.We sketched the posterior neck electron beam irradiation field on the facial mask according to lamplight projection,and calculated the corrected source to film distance by geometry method based on given source to film distance.The leaden blocks were made respectively according to the practical and corrected source to film.Then the patients were moved to the accelerator and localized for radiotherapy.We evaluated the conformance of the radiation fields from both practical and corrected source to film distance while each compared to the original surface mark.Results The corrected source to film distance of each patient is bigger than practical source to film distance.And the field based on practical source to film distance leaded relatively large deviation,which can reach 1.25 cm on maximum.After corrected,the deviation can be narrow down to 0.22 cm.Conclusion Moulding leaden block for posterior neck irradiation based on original image with isocenter point would lead to a relatively large deviation.The leaden block field and the surface mark would fit better by correcting the source to film distance.