Under the skin : Monte Carlo radiation transfer modelling of photodynamic therapy
Abstract
Photodynamic therapy (PDT) is a non-invasive treatment method used for treating superficial
skin lesions such as non-melanoma skin cancer (NMSC). The combination of light, a photo-
sensitive molecule and oxygen results in selective tissue destruction. Even though PDT has
resulted in many successful treatment outcomes, the treatment parameters such as required
light dose and preferred light source have not yet been optimised. Since monitoring of the
treatment progress is limited to surface observations, it is difficult to observe what is happening under the surface of the skin.
In this thesis, the development of complex numerical modelling techniques is considered
with the aim of increasing the understanding of how PDT works within the living skin tis-
sue. In particular, the potential of using daylight as an alternative therapeutic light source is
explored. Daylight PDT is associated with lower experienced pain and has the potential of
reducing pressure on the clinics as well as the number of treatment occasions.
A Monte Carlo radiation transfer (MCRT) model was developed to track photon propagation during treatment. The first theoretical investigation of daylight PDT is presented where
the results indicate a potential treatment depth of over 2 mm, which is sufficient for treating
superficial skin cancer lesions. Additional models are developed, which consider the drug
interaction and the diffusion of the drug. To include different patient characteristics and
more detailed skin models, multi-layered tissue as well as complex three dimensional tumour
tissues are included within the MCRT model framework.
There is no such thing as a generic patient, making it difficult to generate standardised
treatment protocols. The research performed in this thesis provides further insights into light
interaction with skin tissue for different patient and treatment characteristics, which is a vital
step towards achieving more individualised treatment regimes.
Type
Thesis, PhD Doctor of Philosophy
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