Ostapiak O Z, Zhu Y, Van Dyk J
Ontario Cancer Institute, Toronto, Canada.
Med Phys. 1997 May;24(5):743-50. doi: 10.1118/1.597995.
Modern three-dimensional (3-D) photon dose calculation algorithms need to be fast and accurate if they are to be practical for treatment optimization. Refinements to a previously proposed finite-size pencil beam (FSPB) method are presented in order to fulfill these needs. Specifically, a fast Fourier transform (FFT) convolution technique is used to speed calculation of the FSPB; the fluence spectrum is modeled, and the effects of finite source size, a Gaussian x-ray source intensity profile and partial transmission through a multileaf collimator (MLC) leaf are approximated. The use of FFT techniques in the calculation of small diverging fields involves approximations that are investigated for a 6 MV beam and shown to introduce errors that vary with energy but do not exceed 0.7% on the central axis. Dose distributions calculated by FSPB superposition are in excellent agreement with those calculated by full field FFT convolution. Two key advances over the original implementation of the FSPB model are demonstrated: the fast calculation of the FSPB facilitates development, and the incorporation of realistic beam parameters enables accurate modeling of clinical beams.
现代三维（3-D）光子剂量计算算法若要在治疗优化中具有实用性，就需要快速且准确。为满足这些需求，本文对先前提出的有限尺寸笔形束（FSPB）方法进行了改进。具体而言，采用快速傅里叶变换（FFT）卷积技术来加速FSPB的计算；对注量谱进行建模，并近似考虑有限源尺寸、高斯X射线源强度分布以及通过多叶准直器（MLC）叶片的部分透射的影响。在小发散野的计算中使用FFT技术涉及一些近似，针对6兆伏的射束对这些近似进行了研究，结果表明这些近似所引入的误差随能量变化，但在中心轴上不超过0.7%。通过FSPB叠加计算得到的剂量分布与通过全场FFT卷积计算得到的剂量分布高度吻合。文中展示了相对于FSPB模型原始实现的两个关键进展：FSPB的快速计算便于开发，而纳入实际射束参数能够对临床射束进行精确建模。
