Murrer L H, Marijnissen H P, Star W M
Department of Radiation Oncology, University Hospital Rotterdam-Daniel Den Hoed Cancer Centre, The Netherlands.
Lasers Surg Med. 1998;22(4):193-206. doi: 10.1002/(sici)1096-9101(1998)22:4<193::aid-lsm3>3.0.co;2-k.
Light dosimetry for endobronchial photodynamic therapy is not very advanced to date. This study investigates the dependency of the fluence rate distribution in the bronchial wall on several parameters.
STUDY DESIGN/MATERIALS AND METHODS: A Monte Carlo model is employed for the illumination of a cylindrical cavity by a linear diffuser to compute the fluence rate distribution in the tissue. The influence of optical and geometrical properties (e.g., the absorption coefficient of the bronchial mucosa and the diameter of the treated lumen) have been investigated, as well as the consequences of varying output characteristics of the diffusers. The optical properties used are those of ex vivo pig bronchial mucosa.
With on-axis linear diffusers that can be modelled as a row of isotropic point sources, a constant fluence rate buildup factor can be employed for varying diffuser lengths and lumen diameters. Extreme off-axis placement of the diffuser causes a highly variable, considerable increase in the maximum fluence rate as well as a highly asymmetrical fluence rate profile on the circumference of the illuminated lumen. The fluence rate profiles resulting from illumination with realistic diffusers can be evaluated by implementing the measured radiance profiles of these diffusers in the model. The changes in fluence rate caused by variations in the optical properties of the bronchial mucosa could be accounted for by diffusion theory. This relationship can be used to extrapolate the ex vivo results to the clinical situation.
A set of practical rules of thumb is presented that can help to estimate fluence rate distributions in clinical practice.
迄今为止，支气管内光动力疗法的光剂量学发展尚不十分先进。本研究调查了支气管壁中注量率分布对多个参数的依赖性。
研究设计/材料与方法：采用蒙特卡罗模型，通过线性扩散器对圆柱形腔体进行照明，以计算组织中的注量率分布。研究了光学和几何特性（如支气管黏膜的吸收系数和治疗管腔的直径）的影响，以及扩散器输出特性变化的后果。所使用的光学特性为离体猪支气管黏膜的光学特性。
对于可建模为一排各向同性点光源的同轴线性扩散器，对于不同的扩散器长度和管腔直径，可采用恒定的注量率积累因子。扩散器在轴外的极端放置会导致最大注量率出现高度可变且显著的增加，以及在被照明管腔的圆周上出现高度不对称的注量率分布。通过在模型中实现这些扩散器的实测辐射率分布，可以评估用实际扩散器照明所产生的注量率分布。支气管黏膜光学特性变化引起的注量率变化可用扩散理论来解释。这种关系可用于将离体结果外推至临床情况。
提出了一套实用的经验法则，有助于在临床实践中估计注量率分布。
