Chui C S, Mohan R
Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York 10021.
Med Phys. 1988 Mar-Apr;15(2):138-44. doi: 10.1118/1.596267.
A method has been developed to extract pencil beam kernels from measured broad beam profiles. In theory, the convolution of a symmetric kernel with a step function will yield a function that is symmetric about the inflection point. Conversely, by deconvolution, the kernel may be extracted from a measured distribution. In practice, however, due to the uncertainties and errors associated with the measurements and due to the singularities produced in the fast Fourier transforms employed in the deconvolution process, the kernels thus obtained and the dose distributions calculated therefrom, often exhibit erratic fluctuations. We propose a method that transforms measured profiles to new, modified distributions so that they satisfy the theoretical symmetry condition. The resultant kernel from the deconvolution is then free of fluctuations. We applied this method to compute photon and electron dose distributions at various depths in water and electron fluence distributions in air. The agreement between measured and computed profiles is within 1% in dose or 1 mm in distance in high dose gradient regions.
已开发出一种从测量的宽束轮廓中提取笔形束核的方法。理论上，对称核与阶跃函数的卷积将产生一个关于拐点对称的函数。相反，通过反卷积，可以从测量分布中提取核。然而，在实际中，由于与测量相关的不确定性和误差，以及反卷积过程中使用的快速傅里叶变换产生的奇异性，由此获得的核以及从中计算出的剂量分布，常常表现出不稳定的波动。我们提出一种方法，将测量轮廓转换为新的、经过修正的分布，使其满足理论对称条件。然后，反卷积得到的核就没有波动了。我们应用此方法计算了水中不同深度处的光子和电子剂量分布以及空气中的电子注量分布。在高剂量梯度区域，测量轮廓与计算轮廓之间的剂量一致性在1%以内，距离一致性在1毫米以内。
