In-vivo Evaluation And Control Of Light Dose In Photodynamic Therapy For Port Wine Stains

Port wine stains(PWS)is a congenital disease,which mainly occurs on the face and neck.PWS even lead to disfigurement,with serious psychological burden to patients.At present,photodynamic therapy(PDT)is used for the treatment of PWS.However,For different individuals or tissues,personalized treatment is essential.Because the lacking of quantitative calculation and projection method of light dose,the treatment effectiveness of PWS is poor and the treatment cycle is very long.The distribution of optical parameter and photosensitizer can be measured by effective assessment method,which provides the basis for the quantitative calculation and control of light dose in PDT.In this paper,We studied light dose in PDT and developed a system.The system not only can measure the distribution of optical parameters and photosensitizer simultaneously,but also can realize the quantitative projection of the light dose in PDT.It has features of non-contact and non-invasive detection,wide field illumination,and high speed measurement,which enables it suit for the in-vivo assessment and therapy of PWS.To obtain the distribution of surface light source in PDT for PWS.Firstly,the optical parameters model of the skin tissue is calculated and established.The absorption coefficient and scattering coefficient of the whole blood were calculated,and the optical parameters of different-grades PWS were determined according to the theory of capillary morphology and the percentage of volume of capillaries.Thus,a theoretical basis for the calculation of light dose in PDT were developed.Secondly,a calculation method of quantitative light dose in PDT was established,and the method was validated by a series of simulation experiments.Including the situation of surface light sources and lesion areas are one-to-one corresponding and the situation of a number of light sources are corresponding to one lesion area.Further,the influence of light source refinement is analyzed,and the result shows that the finer the calculation grid of light source is,the more favorable for the quantitative of light dose calculation is.We used look-up table method to measure the optical parameters of tissue with a standard phantom acting as a reference,and the results show that the relative error of optical parameters determination is between-7%and + 10%.Next,we discussed the influence of the error on the calculation of light dose.The results demonstrate that the error in determination of optical properties results in a maximum relative error of 27.52%,for thickened nodule region,and a maximum error bellow 10%for other lesions in caculation of light dose.Finally,we constructed the system for quantitative evaluation and the control of light dose in PDT.The system is constitute of the light source projection module,the detection module and mechanical structure.Based on QT graphical interface development tools,integrated control of digital micro-mirror device(DMD),electronic multiplying charge coupled device(EMCCD)and the translation stage is achieved.Experiments were conducted and the results verified the correctness and effectiveness of the integrated program.The system can realize the measurement of optical parameters and photosensitizer,so that the basis for the calculation of light dose distribution in PDT is acquired.Further,quantitative delivery of light dose is achieved.