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Proceedings Paper

Using fluorescence to augment the efficacy of photodynamic therapy
Author(s): Dwayne J. Dickey; Weiyang Liu; Selvaraj Naicker; Thomas Woo; Ronald B. Moore; John Tulip
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Paper Abstract

Photodynamic Therapy (PDT) is a relatively novel oncological treatment modality, in which a patient is administered a photosensitive drug, called a photosensitizer. After allowing sufficient time for biodistribution, the cancerous area is irradiated with light of the appropriate wavelength, activating the photosensitizer to produce highly reactive singlet oxygen, which produces a highly localized cell kill. The efficacy of PDT is determined by a) the intensity of the light b) the local concentration of the photosensitizer, and c) the availability of oxygen. However, with the clinical application of PDT, the patient is simply administered a body mass dependent quantity of photosensitizer, and then the target area is administered a prescribed amount of radiant energy (joules per cubic centimetre). For treatment of superficial malignancies, PDT has many successes; however, interstitial PDT (PDT of solid, internal malignancies) has inconsistent outcomes mostly due to the inability to predict, calculate or measure the variables that affect PDT: the radiation dose, oxygen concentration, and the photosensitizer concentration. We have developed sophisticated methods to determine the behaviour of light in homogeneous biological tissues. Tissue oxygen levels can be replenished by fractionating the light dose - allowing areas of your target tissue to go through a "dark" cycle during PDT. However, to date, there has not been an accurate method of determining tissue photosensitizer concentrations in-vivo. We are researching the efficacy of a novel hypocrellin derivative, SL-052. Like other photosensitizers available, SL-052 shows strong therapeutic photodynamic activity when irradiated by 635 nm light. Like most photosensitizers, SL-052 exhibits fluorescent activity, but SL-052 also shows strong fluorescent emission at 725nm when excited by 635 nm. The intensity of the fluorescent emission can been correlated with the local concentration of the photosenstizer. However, many clinically available photosensitizers require that fluorescence is excited using a wavelength of light much shorter than the therapeutic wavelength. This characteristic allows us to monitor the availability of the photosensitizer during PDT and to correlate the outcome of PDT to the observed fluorescence. In this paper, we monitor the temporal distribution of SL-052 in the Dunning R3327-AT cell line grown on the flank of a Fisher Copenhangen rats.

Paper Details

Date Published: 8 September 2006
PDF: 8 pages
Proc. SPIE 6343, Photonics North 2006, 634305 (8 September 2006); doi: 10.1117/12.706549
Show Author Affiliations
Dwayne J. Dickey, Quest Pharmatech Inc. (Canada)
Weiyang Liu, Univ. of Alberta (Canada)
Selvaraj Naicker, Quest Pharmatech Inc. (Canada)
Thomas Woo, Quest Pharmatech Inc. (Canada)
Ronald B. Moore, Cross Cancer Institute (Canada)
John Tulip, Univ. of Alberta (Canada)

Published in SPIE Proceedings Vol. 6343:
Photonics North 2006
Pierre Mathieu, Editor(s)

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