Whitehurst C, Pantelides M L, Moore J V, Blacklock N J
Department of Experimental Radiation Oncology, Paterson Institute for Cancer Research, Christie Hospital, Manchester, UK.
Photochem Photobiol. 1993 Oct;58(4):589-93. doi: 10.1111/j.1751-1097.1993.tb04937.x.
The understanding of light distribution within the target organ is essential in ensuring efficacy and safety in photodynamic therapy (PDT). A computer simulator of light distribution in prostatic tissue was employed for optimizing dosimetry for PDT in localized prostatic cancer. The program was based on empirically determined light distributions and optical constants and an assumed fluence rate differential from fiber source to necrosis periphery. The diffusion theory approximation to the Boltzmann transport equation was the applicable formulation relevant to prostatic tissue, which has a high albedo with forward-scattering characteristics. Solving this equation of diffusive transfer for the appropriate fiber geometry yielded the energy fluence distributions for cleaved fiber and cylindrical diffuser light delivery. These distributions, confirmed by our measurements, show a 1/r and 1/square root of r dependency (r = distance from light source) of the fluence phi (r) for the cleaved fiber and diffuser, respectively. This manifests itself by the tighter spacing of energy fluence isodoses in the case of the cleaved fiber. It was predicted that for a typical PDT regime a single interstitially placed cleaved fiber would treat 0.05-0.72 cm3. Four parallel fibers improved the uniformity of light distribution and treatment volume, and an interfiber separation of 12 mm would be necessary to provide optimal overlap of PDT necrosis, treating 0.26-3.6 cm3. The cylindrical diffuser, however, could treat larger volumes, and it was predicted that four 3 cm long diffusers at an optimal separation of 25 mm would treat 25-88 cm3 of prostatic tissue.
了解目标器官内的光分布对于确保光动力疗法（PDT）的疗效和安全性至关重要。采用了一种前列腺组织光分布的计算机模拟器来优化局限性前列腺癌PDT的剂量测定。该程序基于经验确定的光分布、光学常数以及从光纤源到坏死周边的假定注量率差异。对玻尔兹曼输运方程的扩散理论近似是适用于前列腺组织的公式，前列腺组织具有高反照率和前向散射特性。针对合适的光纤几何形状求解这个扩散传输方程，得到了劈开光纤和圆柱形扩散器光传输的能量注量分布。经我们测量证实，这些分布分别显示了劈开光纤和扩散器的注量φ(r)对1/r和1/√r的依赖性（r = 距光源的距离）。在劈开光纤的情况下，能量注量等剂量线间距更紧密就体现了这一点。据预测，对于典型的PDT方案，单根间隙放置的劈开光纤可治疗0.05 - 0.72 cm³。四根平行光纤改善了光分布的均匀性和治疗体积，为提供PDT坏死的最佳重叠，纤维间间距需为12 mm，可治疗0.26 - 3.6 cm³。然而，圆柱形扩散器可治疗更大的体积，据预测，四个3 cm长、最佳间距为25 mm的扩散器可治疗25 - 88 cm³的前列腺组织。
