A number of heating sources are available for minimally invasive thermal therapy of tumours. The purpose of this work was to compare, theoretically, the heating characteristics of interstitial microwave, laser and ultrasound sources in three tissue sites: breast, brain and liver. Using a numerical method, the heating patterns, temperature profiles and expected volumes of thermal damage were calculated during standard treatment times with the condition that tissue temperatures were not permitted to rise above 100 degrees C (to ensure tissue vaporization did not occur). Ideal spherical and cylindrical applicators (200 microm and 800 microm radii respectively) were modelled for each energy source to demonstrate the relative importance of geometry and energy attenuation in determining heating and thermal damage profiles. The theoretical model included the effects of the collapse of perfusion due to heating. Heating patterns were less dependent on the energy source when small spherical applicators were modelled than for larger cylindrical applicators due to the very rapid geometrical decrease in energy with distance for the spherical applicators. For larger cylindrical applicators, the energy source was of greater importance. In this case, the energy source with the lowest attenuation coefficient was predicted to produce the largest volume of thermally coagulated tissue, in each tissue site.

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This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer.The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction.In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion.Oversize materials (e-g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book.Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6* x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. The author retains ownership of the L'auteur conserve la propriete du copyright in t h~s thesis. Neither the droit d'auteur qui protege cette these. thesis nor substantial extracts from it Ni la these ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent Etre imprimes reproduced without the author's ou autrement reproduits sans son permission.autorisation. Department of Medical BiophysicsThe University of Toronto. 1998 Lasers can be used to heat and destroy cancer cells by delivering light via fiber directly into a tumour. in a novel and promising procedure called Interstitial Laser Photocoagulation (ILP). Thermal lesion formation during ILP is a dynamic process involving many heat induced alterations of tissue such as changes in optical properties and blood perfusion. However. the effects of these changes on the outcome of lesion formation are not well understood. Therefore. thermal models are being developed to investigate the importance of the effects on predicting treatment outcomes. These models are essential for the successful planning of thermal therapy treatments of ILP to achieve complete tumour destruction while sparing normal tissue and avoiding the deleterious effects 2f vapourization and charring.The aim of our work is t o propose and validate a model which incorporates heat induced changes of optical properties due to coagulation by solving the nonlinear bioheat equation. The dynamic effects are modeled based on the Arrhenius damage formulation which describes thermal damage as an irreversible rate process. The validity of the model assumptions was investigated experimentally by developing novel opto-thermal phantoms with properties similar to those of tissu...

Background and Objective: Phantoms were developed that simulate tissue with dynamic and static optical properties with which to study the effects of laser irradiation. Study Design/Materials and Methods: Albumen, agar, and an absorbing dye (Naphthol Green) were combined to form a phantom with heat sensitive optical properties to mimic tissue response. The optical properties of this phantom were measured by using the added absorber technique. A polyacrylamide phantom with static optical properties was designed with the equivalent values of a and s by combining appropriate concentrations of Naphthol Green and Intralipid-10%.

One effect of heating during interstitial laser photocoagulation (ILP) is to directly destroy the tumour vasculature resulting in a loss of viable blood supply. Therefore, blood flow measured during and after treatment can be a useful indicator of tissue thermal damage. In this study, the effect of ILP treatment on rabbit thigh tumours was investigated by measuring blood flow changes using dynamic contrast enhanced computed tomography (CT). The CT measured changes in blood flow of treated tumour tissue were fitted to an Arrhenius model assuming first order rate kinetics. Our results show that changes in blood flow of tumour tissue distant from surrounding normal tissue are well described by an Arrhenius model. By contrast, the temperature profile of tumour tissue adjacent to normal tissue must be modified to account for heat dissipation by the latter. Finally, the Arrhenius parameters derived in the study are similar to those derived by heating tumour tissue to a lower temperature (<47 degrees C) than the current study. In conclusion, CT can be used to monitor blood flow changes during ILP and these measurements are related to the thermal damage predicted by the Arrhenius model.

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