Murrer L H, Marijnissen J P, Star W M
Department of Clinical Physics, Dr Daniel Den Hoed Cancer Centre, Erasmus University Hospital, Rotterdam, The Netherlands.
Phys Med Biol. 1995 Nov;40(11):1807-17. doi: 10.1088/0031-9155/40/11/003.
The light distribution during photodynamic therapy of the bronchial tree has been estimated by measuring the fluence rate in ex vivo experiments on dissected pig bronchi. The trachea was illuminated (630 nm) with a cylindrical diffuser and the fluence rate was measured with a fibre optic isotropic probe. The experiment with the diffuser on the central axis was also simulated with Monte Carlo techniques using the optical properties that were determined with a double-integrating-sphere set-up. The results from ex vivo experiments and the Monte Carlo simulations were found to agree within the error of measurement (15%), indicating that the Monte Carlo technique can be used to estimate the light distribution for varying geometries and optical properties. The results showed that the light fluence rate in the mucosa of the tracheal tract may increase by a factor of six compared to the fluence rate in air (in the absence of tissue). This is due to the scattering properties of the tissue and the multiple reflections within the cavity. Further ex vivo experiments showed that the positioning of the diffuser is critical for the fluence rate in the lesion to be treated. When the position of the diffuser was changed from the central axis to near the lesion, the fluence rate in the mucosa increased significantly by several orders of magnitude as compared to the initial (central) illumination. The inter- and intraspecimen variations in this increase were large (+/- 35%) because of variations in optical and geometrical properties and light source positioning, respectively. These variations might cause under- or overdosage resulting in either insufficient tumour necrosis or excessive normal tissue damage.
通过在离体猪支气管实验中测量注量率，估算了支气管树光动力治疗期间的光分布。用圆柱形漫射器照射气管（630纳米），并用光纤各向同性探头测量注量率。还使用蒙特卡罗技术，利用双积分球装置测定的光学特性，模拟了漫射器位于中心轴上的实验。发现离体实验结果与蒙特卡罗模拟结果在测量误差（15%）范围内相符，这表明蒙特卡罗技术可用于估算不同几何形状和光学特性下的光分布。结果表明，与空气中（无组织时）的注量率相比，气管黏膜中的光注量率可能会增加6倍。这是由于组织的散射特性以及腔内的多次反射。进一步的离体实验表明，漫射器的位置对于待治疗病变中的注量率至关重要。当漫射器的位置从中心轴移至靠近病变处时，与初始（中心）照射相比，黏膜中的注量率显著增加了几个数量级。由于光学和几何特性以及光源位置的变化，这种增加在样本间和样本内的差异很大（±35%）。这些差异可能导致剂量不足或过量，从而导致肿瘤坏死不足或正常组织过度损伤。
