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Laser light delivery for photodynamic therapy of hollow organs: a feasibility study

Lunt, Louise; (1997) Laser light delivery for photodynamic therapy of hollow organs: a feasibility study. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

This thesis describes a new laser light delivery system for the Photodynamic Therapy of hollow organs. The system makes use of a photosensitive balloon mask that is inflated within the organ. When irradiated using a bulb-tipped optical fibre, areas of the mask that have allowed a therapeutic dose of radiation to enter the tissue turn opaque due to a light induced increase in either absorption or scattering. This avoids further irradiation and consequent over-treatment of the tissue. A range of polymers and photosensitive materials were studied to determine those which would be most suitable for the construction of the balloon mask. These fall into two categories: (a) Materials which undergo a change in their scattering coefficient. Once the therapeutic dose has been delivered light is deflected to areas which have not yet received the required dose. No suitable material or combination of materials was found, (b) Materials that undergo an increase in their absorption coefficient. Absorption, however, makes less efficient use of incident light. Some materials were found to be adversely affected by the polymer chosen for the balloon. The response of photochromic materials on the other hand was unaffected by latex or polystyrene, the materials chosen as the host for further study of photochromies. Aberchrome 1053, a commercially available photochromic, underwent a significant change in its optical density in either polystyrene or latex. When irradiated by UV light it underwent a change in its optical density at 560 nm from 0.08 to 1.45. A Monte Carlo model in a spherical geometry was used to predict the light distribution produced by a IW isotropic light source when used with a 70 mm balloon incorporating Aberchrome 1053. The variation in the light dose received by the tissue when the source was offset by 20 mm was ± 2%. However, being photo-reversible, Aberchrome 1053 required the use of high levels of the UV activating wavelength to favour the desired forward reaction. With the availability of a thermally reversible photochromic with more favourable reaction kinetics this problem would be overcome. It is concluded that the proposed balloon mask is feasible provided a suitable photochromic or other photochemical becomes available.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Laser light delivery for photodynamic therapy of hollow organs: a feasibility study
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Pure sciences; Hollow organs; Laser light delivery; Photodynamic therapy
URI: https://discovery.ucl.ac.uk/id/eprint/10103984
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