Monte Carlo simulation of intraoperative photodynamic therapy for glioblastoma : investigating dosimetric parameters and treatment efficacy

Abstract

This thesis looks at using Monte Carlo radiative transfer (MCRT) to simulate the path and effect of light as it travels through biological tissue.

The increase in light-based skin treatments and medical technology has resulted in a need for detailed information on the penetration depth of light into skin. A 6-layer skin model is developed to simulate the propagation of light from 200 nm - 1000 nm into skin with Fitzpatrick photo-type I. The effect of varying stratum corneum thickness and light incident angle is investigated before looking at the lateral spread of a laser beam incident on the skins surface.

Photodynamic therapy (PDT) is a light based therapy currently used or being investigated to treat many different forms of cancer. The combination of treatment light, a photosensitising drug and oxygen result in a localised toxic effect that specifically targets cancer cells. The MCRT code is used to develop a time dependant simulation of PDT, considering the treatment light fluence rate and local concentrations of photosensitiser and oxygen. This allows different PDT protocols to be simulated and compared.

Glioblastoma (GBM) is an aggressive and difficult to treat form of brain tumour. It has a low survival rate due to the tumours highly diffusive nature, resulting in a high rate of recurrence. A recent clinical trial aimed to increase this survival time by intraoperatively treating the resection cavity with PDT at the end of resection surgery to increase the extent of resection. The MCRT/PDT simulation is used to model this protocol and investigate the effect on tumour cell kill when varying several treatment parameters such as treatment time, light power and photosensitiser concentration. Finally, a heat transport simulation is also used to investigate the effect of intraoperative PDT treatment on the temperature of the surrounding brain tissues.