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首页> 外文期刊>Medical Physics >The effect of gantry angle on megavoltage photon beam attenuation by a carbon fiber couch insert.
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The effect of gantry angle on megavoltage photon beam attenuation by a carbon fiber couch insert.

机译：台架角度对碳纤维床插入件对兆伏光子束衰减的影响。

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摘要

The use of rigid carbon fiber couch inserts in radiotherapy treatment couches is a well-established method of reducing patient set-up errors associated with couch sag. Several published studies have described such inserts as radiotranslucent with negligible attenuation of the radiation field. Most of these studies were conducted with the radiation field normally incident on the couch and there appears to be no evidence in the literature of the effect of the gantry angle on the extent of beam attenuation by the carbon fiber insert alone during external beam radiotherapy. In this study we examined the magnitude of this effect over a range of posterior oblique gantry angles using a cylindrical solid water phantom containing an ionization chamber placed isocentrically. It was found that a 6 MV photon beam, field size 10 x 5 cm, was attenuated significantly as the gantry angle approached the plane of the couch, from 2% at normal incidence and reaching 9% attenuation at angle of incidence 70 degrees. This could have serious implications regarding dose to the treatment volume for treatments requiring posterior oblique angles of incidence with a possible correction factor necessary in monitor unit calculations.
机译：在放射疗法治疗床中使用硬质碳纤维床插入物是一种行之有效的方法，可减少与床下垂相关的患者站立错误。几项已发表的研究将这种插入物描述为辐射半透明的，而辐射场的衰减可忽略不计。这些研究大多数是在通常入射在沙发上的辐射场下进行的，并且在文献中似乎没有证据表明在外部束放射治疗期间，机架角度对单独碳纤维插入物的束衰减程度的影响。在这项研究中，我们使用包含等离子放置的电离室的圆柱形固体水体模，在后倾斜龙门角度范围内检查了这种效应的强度。已发现，当龙门角度接近沙发平面时，视场大小为10 x 5 cm的6 MV光子束会从法向入射时的2％显着衰减，在入射角70度时达到9％的衰减。对于需要后倾斜入射角的治疗以及在监护仪单位计算中可能需要的校正因子，这可能会对治疗剂量剂量产生严重影响。

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