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 DAPR_20,10, were studied to yield more information on its feasibility over the conventional quality specifier tissue-phantom ratio or TPR_20,10. The DAPR_20,10 may 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 DAPR_20,10 were studied and it was shown that the DAPR_20,10 increases with increasing beam energy similarly to TPR_20,10 but 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 DAPR_20,10. 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.

在小场放射治疗 (RT) 中，一个重大挑战是定义患者吸收的辐射剂量，其中必须以高精度测量光束质量。对提出的新光束质量说明符的特性，即水中 20 和 10 厘米深度或 DAPR _20,10的剂量面积积比进行了研究，以产生更多关于其与传统质量说明符组织模型比的可行性的信息或 TPR _20,10。DAPR _20,10可以使用大面积电离室 (LAC) 来测量，而不是使用检测器、光束和水模体定位以及光束扰动引入不确定性的小体积室或半导体。光束形状、尺寸和能量对 DAPR _{20,10的影响}研究表明，DAPR _{20,10与 TPR 20,10}类似，随着光束能量的增加而增加，但相比之下，光束尺寸和形状依赖性较小。光束限制装置外的光束轮廓已被证明对 DAPR _20,10有很大的贡献。大面积腔室有潜力用于 DAPR 测量及其在用于光束质量测量的小射束 RT 剂量学中的应用。