The aim of this study was to investigate the effects of the propagation speed of a thermal wave in terms of the thermal relaxation time on the temperature/thermal dose distributions in living tissue during thermal therapies. The temperature field in tissue was solved by the finite difference method, and the thermal dose was calculated from the formulation proposed by Sapareto and Dewey [Int. J. Radiat. Oncol. Biol. Phys. 10, 787-800 (1984)]. Under the same total deposited energy, for a rapid heating process the time lagging behavior of the peak temperature became pronounced and the level of the peak temperature was decreased with increasing the thermal relaxation time. When the heating duration was longer than the thermal relaxation time of tissues, there was no significant difference between the thermal dose distributions with/without considering the effect of the thermal relaxation time. In other words, when the heating duration is comparable to or shorter than the thermal relaxation time of tissue, the results of the wave bioheat transfer equation (WBHTE) are fully different from that of the Pennes' bioheat transfer equation (PBHTE). Besides, for a rapid heating process the dimension of thermal lesion was still significantly affected by perfusion, because this is what is predicted by the WBHTE but not by the PBHTE, i.e., the wave feature of the temperature field cannot fully be predicted by the PBHTE.
This study presents the effects of directional blood flow and heating schemes on the distributions of temperature and thermal dose during thermal therapy. In this study, a transient bioheat transfer equation based on the porous medium property is proposed to encompass the directional effect of blood flow. A Green's function is used to obtain the temperature distribution for this modified bioheat transfer equation, and the thermal dose equivalence is used to evaluate the heating results for a set of given parameters. A 10 x 10 x 10 mm3 tumour tissue is heated by different heating schemes to investigate the thermal dose variation with the clinical therapeutic arrangement. For a rapid heating scheme, the domain of thermal lesion can effectively cover the desired therapeutic region. However, this domain of thermal lesion may extend to the downstream normal tissue if the porosity is high and the averaged blood velocity has a larger value.
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