• light emitting diodes
• photodynamic therapy
• radiation dose distribution
• spectroradiometer

Non-melanoma skin cancers (NMSCs) and precancerous skin lesions, such as Actinic Keratosis (AK), are among the most common malignancy-related diseases in the Caucasian population.

Photodynamic therapy (PDT) is a photochemotherapy for NMSC and AK that allows the treatment of large areas of the skin and has a high response rate. Therapy involves the diffusion and activation of light-absorbing dye molecules (Protoporphyrin IX or PpIX) in diseased tissues. The tissue absorption of PpIX occurs after the application of topical creme to the skin.
When the skin is irradiated with specific light wavelengths, activation of the absorbed PpIX causes selective tissue injury and tumour cell death.
PpIX activation strongly depends on the intensity of the source, the duration of treatment, and the wavelengths of the incident radiation. Therefore, the spectral irradiance of the therapy sources should be well-characterised.
Examples of light sources for PDTs are the Sun, lasers, and light-emitting diodes (LEDs). When the source is the Sun, the therapy name is natural daylight PDT (NDL-PDT).

Although PDT has been used in medical treatment for several decades, the irradiation required to achieve effective therapies is still under investigation.
Medical professionals rely on PDT guidelines and lamp treatment protocols to determine the amount of radiation administered to patients.
Despite their expertise, doctors lack the necessary tools to consider crucial factors, such as the source's proximity to the skin or the orientation of the lesions. This can lead to an uneven distribution of the dose on the skin's curved surface and ineffective therapies.

This Master Thesis reports the main results of the development and validation of a 3D model of the distribution of spectral irradiance emitted by LED arrays. Validation of the model includes experimental measurements of the spectral irradiance emitted by commercial PDT therapy lamps using a calibrated spectroradiometer.
In our study, we simulated PDT treatment scenarios on a triangular mesh with a human shape. The simulated sources of therapy are both the modelled lamps and solar radiation.

Data acquisition, instrumental calibration, and model development resulted from 9 months of collaboration with the Laser and Optical Radiation Dosimetry Group of the UK Health and Security Agency (UKHSA), which provided experience, facilities, and experimental tools. The entire study was funded by the company siHealth Ltd.

Our model allows doctors to quantify the dose on each treated lesion, even when the lesions lie on a complex curved skin surface. This work can improve the quality of therapy and lay the foundation for more accurate research on PDT.