Bender Edward T
Department of Human Oncology, School of Medicine and Public Health, University of Wisconsin-Madison, 600 Highland Avenue, Madison, Wisconsin 53792.
Med Phys. 2014 May;41(5):051706. doi: 10.1118/1.4870380.
To investigate the theoretical limits to the tradeoff between dose gradient and uniformity when modulation is used in the context of cone based SRS, and to design a prototype collimation device that allows for steeper dose gradients and/or higher target uniformity as compared to a standard circular collimator.
An inverse planning optimization is performed in the context of idealized phantom geometry to determine the ideal fluence pattern that best approximates a "rect function" dose distribution. Ideal fluence patterns were approximated in a prototype device and radiochromic film dosimetry was utilized to compare the prototype device to a standard circular collimator.
For choices of prescription isodose lines above approximately 50%, utilizing modulation allows for an improved tradeoff between dose gradient index and dose heterogeneity index. Compensators placed within the circular collimator can achieve the necessary modulation.
Using modulation with features on a submillimeter distance scale, it is possible to increase the dose gradient and/or uniformity in small fields.
研究在基于锥形束的立体定向放射治疗（SRS）中使用调制时剂量梯度与均匀性之间权衡的理论极限，并设计一种原型准直装置，与标准圆形准直器相比，该装置能实现更陡的剂量梯度和/或更高的靶区均匀性。
在理想化的体模几何结构中进行逆向计划优化，以确定最接近“矩形函数”剂量分布的理想注量模式。在原型装置中近似理想注量模式，并利用放射变色薄膜剂量测定法将原型装置与标准圆形准直器进行比较。
对于处方等剂量线高于约50%的选择，使用调制可改善剂量梯度指数与剂量异质性指数之间的权衡。放置在圆形准直器内的补偿器可实现必要的调制。
使用亚毫米距离尺度特征的调制，可以增加小射野中的剂量梯度和/或均匀性。
