Comparison of photon absorption and thermal effect between conventional and interstitial photodynamic therapy using Monte Carlo simulation and agarose gel phantom

Abstract

Photodynamic therapy (PDT) is a form of therapy involving light and a photosensitizing chemical substance, used in conjunction with molecular oxygen to elicit cell death. There are two representative types of PDT – conventional PDT (cPDT) and interstitial PDT (iPDT). In this study, we tried to compare these two methods in terms of photon absorption and thermal effect. Monte Carlo simulation is used in various fields of study such as finance, engineering and it has been regarded as the ‘gold standard’ for simulating light propagation in biological tissue because it is a fundamental and versatile method of modeling light transport in tissues. The movement of photon can be simulated from defined x, y, z coordinates through the tissue medium following its specific optical properties. We utilized a Monte Carlo method to simulate cPDT and iPDT on tumor medium, and the information of magnitude and the distribution of photon absorption within the tumor were extracted. To verify the simulation results, an agarose gel phantom was fabricated and the temperature distribution in the phantom was monitored during cPDT and iPDT. The simulation data showed that iPDT has greater amount of absorbed photons than cPDT, and the temperature distribution in gel phantom also showed higher temperature distribution in the case of iPDT than cPDT. These results proved that iPDT can be more effective in tumor treatment compared to cPDT.