Chang Chang, Wang Ken K-H, Zhu Timothy C
Department of Radiation Oncology, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104.
Proc SPIE Int Soc Opt Eng. 2010 Mar 2;7551. doi: 10.1117/12.843000.
To accurately calculate light fluence rate distribution in prostate photodynamic therapy (PDT), optical heterogeneity has to be taken into account. Previous study has shown that a kernel based on analytic solution of the diffusion equation can perform the calculation with accuracy comparable to Finite-element method. An assumption is made that light fluence rate detected at a point in the medium is affected primarily by the optical properties of points (or elements) on the line between the source and the point. The exponential decay term of the light fluence rate is expressed as an integral of effective attenuation coefficient of each point along the line. The kernel method is first developed for a point source and then extended for a linear source. A linear source is considered being composed of multiple point sources and light fluence rate is summation of the fluence rates generated by the point sources. In this study, we have implemented a fast ray-trace algorithm to substantially speed up the calculation. The kernel calculation is compared with FEM calculation and is examined with light fluence rate measurements. The examination with clinical measurement data shows that calculated fluence rates present similar features in distribution as the measurement, with errors of 30%-70% for the peak fluence rates. We concluded that our heterogeneous algorithm is potentially valuable for light fluence rate optimization during interstitial PDT.
为了准确计算前列腺光动力疗法（PDT）中的光通量率分布，必须考虑光学不均匀性。先前的研究表明，基于扩散方程解析解的核可以实现与有限元方法相当的精度计算。假设在介质中某一点检测到的光通量率主要受源点与该点之间连线上各点（或单元）光学特性的影响。光通量率的指数衰减项表示为沿该线各点有效衰减系数的积分。核方法首先针对点光源开发，然后扩展到线光源。线光源被视为由多个点光源组成，光通量率是这些点光源产生的通量率之和。在本研究中，我们实现了一种快速光线追踪算法，以大幅加快计算速度。将核计算与有限元计算进行比较，并通过光通量率测量进行检验。临床测量数据检验表明，计算得到的通量率分布特征与测量结果相似，峰值通量率误差为30%-70%。我们得出结论，我们的非均匀算法在间质光动力疗法中对光通量率优化具有潜在价值。
