[Objective] To present a more effective way to determinate the target volume in electron beam irradiation while using three-dimensional treatment planning system.[Methods] Contoured the target volume according to the images from CT simulation,and designed the electron beam irradiation field by using 3DTPS.Calculated the shifting coordinate of irradiation field based on the original coordinate.Installed the applicator with the leaden block of electron beam onto the accelerator.Turned on the lamp field and marked the cross line on the plate.A foam mould which was marked with filed centre and direction should be cutted based on the DR image from TPS.The leaden block would be made on a premise that the cross lines on the plate and the foam were coincident.Evaluated the feasibility of this method by radiotherapy verification.[Results] The offset degree of target centre was less than 2.2 mm,also the maximum deviation is less than 1.7 mm.[Conclusion] The method that coincide the irradiation field centre and the centre from TPS can solve the problem of target area's variation.Also the method can ensure the process of electron irradiation going smoothly.

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.

临床应用电子束放疗时常常会遇到不对称野,如乳腺癌术后胸壁电子线照射、鼻咽癌后上颈电子线补量照射等.不对称野通常是指限光筒上铅挡野中心偏离标准限光筒射束中心,临床上在进行射野设计、能量选择和剂量计算时需了解不同大小、不同偏轴位置的不对称野的电子束特性。

Purpose:Research about the method and clinical application of postural fixation adding on the broad of simulated positioner.Method:Using formed hot press molding to sampling on the broad of accelerator provided with fixture.As the way mentioned above to sample on the simulated positioner.Mark the relevant position of broad,and adding the fixture.Results:Observing 270 patients with first accelerated therapy.Conclusion:Comparing there graticule,we can get that this method(introduced in this paper) can make the mistake within 2mm.So,it is worth to promote in the hospital with same level.