Farina B, Saponaro S, Pignoli E, Tomatis S, Marchesini R
Istituto Nazionale per lo Studio e la Cura dei Tumori, Milan, Italy.
Phys Med Biol. 1999 Jan;44(1):1-11. doi: 10.1088/0031-9155/44/1/002.
The propagation of light emitted by a linear light diffuser in a cylindrical hollow organ was investigated by means of the Monte Carlo (MC) method. The height and radius of the cavity, scattering (mu(s)) (or reduced scattering, mu'(s)) and absorption (mu(a)) coefficients, anisotropy (g), and refractive indices of the media involved (n1, n2) are required as input data by the MC code, as are characteristics of the light diffuser (length, delivered power and emission profile). Results of our MC model were tested by measuring the light fluence rate in a tissue-simulating phantom (mu(a) = 0.5 cm(-1), mu(s) = 23 cm(-1) and g = 0.75) irradiated at 633 nm with a cylindrical diffuser. Since geometric and optical parameters determine the behaviour of light propagation in tissue, MC simulations with different sets of input parameters were carried out to provide qualitative as well as quantitative data useful in planning photodynamic therapy. Data are reported on light penetration and fluence rate build-up at mu(a) and mu'(s) values ranging between 0.1 and 5 cm(-1) and 2.5 and 50 cm(-1), respectively. Furthermore, results suggest that a shift and spread could occur in the isofluence curves along the symmetry axis, which depend on the diameter of the treated lumen as well as on the emission profile of the light diffuser. Using our data it is possible to estimate how inaccuracy in knowledge of the optical coefficients can affect (i.e. usually by increasing) the light dose scheduled at a certain depth into tissue.
采用蒙特卡罗（MC）方法研究了线性光扩散器发出的光在圆柱形中空器官中的传播。MC代码需要腔体的高度和半径、散射系数（μ(s)）（或约化散射系数，μ'(s)）、吸收系数（μ(a)）、各向异性（g）以及所涉及介质的折射率（n1、n2）作为输入数据，还需要光扩散器的特性（长度、输出功率和发射轮廓）。通过测量用圆柱形扩散器在633nm波长下照射的组织模拟体模（μ(a)=0.5cm⁻¹，μ(s)=23cm⁻¹，g=0.75）中的光通量率，对我们的MC模型结果进行了测试。由于几何和光学参数决定了光在组织中的传播行为，因此进行了不同输入参数集的MC模拟，以提供在光动力治疗规划中有用的定性和定量数据。报告了分别在μ(a)值介于0.1和5cm⁻¹之间以及μ'(s)值介于2.5和50cm⁻¹之间时的光穿透和通量率积累的数据。此外，结果表明，等光强曲线可能会沿着对称轴发生偏移和展宽，这取决于治疗管腔的直径以及光扩散器的发射轮廓。利用我们的数据，可以估计光学系数知识的不准确会如何影响（即通常是增加）预定在组织中某一深度的光剂量。
