Zhu X R, Low D A, Harms W B, Purdy J A
Mallinckrodt Institute of Radiology, Washington University School of Medicine, Saint Louis, Missouri 63110, USA.
Med Phys. 1995 Aug;22(8):1315-27. doi: 10.1118/1.597516.
A convolution-adapted ratio of tissue-air ratios (CARTAR) method of dose calculation has been developed at the Mallinckrodt Institute of Radiology. This photon pencil-beam algorithm has been developed and implemented specifically for three-dimensional treatment planning. In a standard ratio of tissue-air ratios (RTAR) algorithm, doses to points in irregular field geometries are not adequately modeled. This is inconsistent with the advent of conformal therapy, the goal of which is to conform the dose distribution to the target volume while sparing neighboring sensitive normal critical structures. This motivated us to develop an algorithm that can model the beam penumbra near irregular field edges, while retaining much of the speed for the original RTAR algorithm. The dose calculation algorithm uses two-dimensional (2D) convolutions, computed by 2D fast Fourier transform, of pencil-beam kernels with a beam transmission array to calculate 2D off-axis profiles at a series of depths. These profiles are used to replace the product of the transmission function and measured square-field boundary factors used in the standard RTAR calculation. The 2D pencil-beam kernels were derived from measured data for each modality using commonly available dosimetry equipment. The CARTAR algorithm is capable of modeling the penumbra near block edges as well as the loss of primary and scattered beam in partially blocked regions. This paper describes the dose calculation algorithm, implementation, and verification.
马林克罗特放射研究所开发了一种适用于卷积的组织空气比（CARTAR）剂量计算方法。这种光子笔形束算法是专门为三维治疗计划而开发和实施的。在标准的组织空气比（RTAR）算法中，对不规则野几何形状中点的剂量建模不够充分。这与适形治疗的出现不一致，适形治疗的目标是使剂量分布与靶体积相符，同时保护相邻的敏感正常关键结构。这促使我们开发一种算法，该算法可以对不规则野边缘附近的射束半值层进行建模，同时保持原始RTAR算法的大部分速度。剂量计算算法使用二维（2D）卷积，通过2D快速傅里叶变换将笔形束核与射束传输阵列进行卷积，以计算一系列深度处的二维离轴剖面。这些剖面用于替代标准RTAR计算中使用的传输函数与测量的方形野边界因子的乘积。二维笔形束核是使用常用的剂量测定设备从每种模态的测量数据中推导出来的。CARTAR算法能够对遮挡边缘附近的半值层以及部分遮挡区域中的原发射线和散射线损失进行建模。本文描述了剂量计算算法、实现和验证。
