Optical modelling points the way to PDT progress

ASAP BIO ARTICLE
O L E • A p r i l 2 0 0 9 • o p t i c s . o r g /o l e

Off-the-shelf commercial software is helping scientists to enhance the clinical efficacy of

photodynamic therapy for targeted tumour destruction. Joe McEntee reports.

PDT is a two-stage process that exploits the activation of a photosensitive drug by using

light to destroy cancer cells. In the first step, a photosensitizer is administered to the patient, either topically

or via injection. After an appropriate time period, depending on the particular drug

used and the targeted treatment area, much of the photosensitizer will have preferentially

accumulated in the abnormal tissue.

The second stage is the irradiation of the tumour site with light of a wavelength that

will be absorbed by the photosensitizer. Once activated, the drug produces cytotoxic singlet

oxygen, which damages cellular membranes and causes cell death. By careful targeting of

this light (most commonly provided by a laser), PDT selectively destroys abnormal tissue.

Model behaviour: optical scientist Kit Cheong of BRO views a tissue-optics simulation using the

Realistic Skin Model in ASAP. The software can model the light dose deposited in target tissues