Abstract-This paper is to study the accessible depth by photons within biological tissue for Photodynamic Therapy of cancer. For the measurements of light propagation within tissue, we applied the diode Laser of 660nm wavelength and by assuming the medium to be homogeneous, we neglect the effects of any refractive index mismatches between the tissue layers. The result have yielded the penetration depth of light within biological tissue. Keywords -Photodynamic Therapy, Light Propagation, Diode Laser.
I. INTRODUCTIONPhotodynamic therapy is an effective method to treat cancer by means of light action on photosensitizer in tissue. It is considered that destroying effect is mainly due to the formation of singlet oxygen resulting from the interaction of light excited photosensitizer with molecular oxygen (triplet state in the ground state). So the destroying effect will be proportional to the rate of singlet oxygen formation which is in turn depends on light intensity, photosensitizer concentration and molecular oxygen concentration [1].Proper intensity of laser could determined by the measurement of propagation of light within normal and cancer tissues. For the effective PDT, we should controlled the value of photosensitizer, power density of laser and supplied oxygen to tissue. Increasing the power density of laser has problem like heating damage of tissues from laser [2,3]. High intensity of laser leads interaciton of light excited photosensitizer with molecular oxygen activity. It makes the blood oxygen saturation decrease. The interaction is also decreased due to insufficient oxygen. Stopping of irradiation increase the interaction means that pulse type of irradiation is effective method for the PDT.We measure the light propagation within biological tissue as post steps of determine the property condition of PDT like as intensity of laser power and irradiation time control.II. METHODOLOGY 1. Experimental diode Laser System Diode laser resonator, 660nm wavelength and 300mW maximum power, was used in this measurement. Diode laser system was consist of CPU, Key Input, LCD Display, Laser Resonator. Laser Power Supply and Laser Power controller. Fig.1. shows the block diagram of diode laser system. Irradiation time and frequency were changed from 10m second to 99 second on/off time by setting for variable measurement conditions. Power density was also changed 10mW/cm 2 ~ 300mW/cm 2 by controller.
Measurement of light propagationThe characterstic of light within tissue is summarized reflection, absorption, scattering and penetration [4,5,6]. We measured scattering and penetration depth within biological tissue by spectroscopy. Fig. 2. shows measurement method. Light through the sample tissue was detected by spectrometer.
Fig. 2. Method of measurement of light propagationWe investigated the heating damage of tissue with microscope after exposed by continuous wave form. 200mW/cm2 of power density was free from heating damage. This power was fixed to peak power of pulse waveform. We measured power density through variable...