In small-field radiotherapy (RT), a significant challenge is to define the amount of radiation dose absorbed in the patient where the quality of the beam has to be measured with high accuracy. The properties of a proposed new beam quality specifier, namely the dose-area-product ratio at 20 and 10 cm depths in water or DAPR20,10, were studied to yield more information on its feasibility over the conventional quality specifier tissue-phantom ratio or TPR20,10. The DAPR20,10may be measured with a large-area ionization chamber (LAC) instead of small volume chambers or semi-conductors where detector, beam and water phantom positioning and beam perturbations introduce uncertainties. The effects of beam shape, size and energy on the DAPR20,10were studied and it was shown that the DAPR20,10increases with increasing beam energy similarly to TPR20,10but in contrast exhibits a small beam size and shape dependence. The beam profile outside the beam limiting devices has been shown to have a large contribution to the DAPR20,10. There is potential in large area chambers to be used in DAPR measurement and its use in dosimetry of small-beam RT for beam quality measurements.

中文翻译：

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外部小束放射治疗的剂量-面积乘积比：临床光子束的束形状，大小和能量依赖性。

在小视场放射治疗（RT）中，一项重大挑战是定义必须精确测量光束质量的患者吸收的辐射剂量。研究了拟议的新型光束质量说明器的特性，即在20或10厘米深度处的剂量-面积比或水或DAPR20,10，以提供有关其优于常规质量说明器组织-体模比或TPR20，10。DAPR20,10可以使用大面积电离室（LAC）来代替，而不是用于检测器，电子束和水体模的定位以及电子束扰动会带来不确定性的小体积电子室或半导体。研究了光束形状，大小和能量对DAPR20,10的影响，结果表明，与TPR20类似，DAPR20,10随着光束能量的增加而增加，与之相反，图10所示的光束具有较小的光束尺寸和形状依赖性。光束限制装置外部的光束轮廓已显示出对DAPR20,10的巨大贡献。大面积腔室有潜力用于DAPR测量，以及在小束RT剂量学中用于光束质量测量的潜力。