Patterns of changes of tumour temperatures during clinical hyperthermia: Implications for treatment planning, evaluation and control

Abstract

The patterns of changes in tumour temperatures were studied at selected times throughout 104 hyperthermia sessions. Temperature change patterns were analysed in the context of the known patterns of change of the applied power. First, of 69 extracranial treatments analysed, 74% indicated relatively flat temperatures at constant applied power during a major portion of the treatment, thereby indicating that during that time there were no major changes in any of the physical or physiological tissue parameters which contribute to the ability of the tumour tissue to remove energy (Pattern 1). Second, after reaching an initial steady state, approximately 14% of these extracranial treatments showed either steadily decreasing temperatures at constant power, or constant temperatures at steadily increasing applied power, thereby indicating that the tumour's ability to remove energy was steadily increasing in time following the initial steady state (Pattern 2). Finally, after reaching an initial steady state, the remaining 12% of these treatments showed a pronounced decrease in temperature occurring about 10-20 min into the treatment followed by increasing temperatures or levelling off of temperatures at a higher value than the temperature minimum that had occurred, all at constant applied power (Pattern 3). Of 35 brain treatments analysed, 80% followed Pattern 1, 14% followed Pattern 2, and 6% followed Pattern 3. Intratumoral heterogeneity was evident in some cases with approximately 44% of all treatments having at least one individual temperature sensor change in a manner that did not follow the average direction of change when all sensors were combined. For seven patients with permanent probes, the patterns of change presented in the first treatments were also observed during six out of seven of the second treatments. In addition, three out of the five patients who had an evaluable third treatment showed a pattern of change during that third treatment that was similar to the pattern observed in both treatment one and treatment two.

Ultrasound hyperthermia control system for deep-seated tumours: Ex vivo study of excised tumours, modeling of thermal profile and future nanoengineering aspects

“…The air bubbles pulsation absorbs acoustical energy and increases the tissue heating. The presence of cavitation bubbles in front of the transducer focus results in nonsymmetrical lesion positioning with respect to the transducer focus [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40].…”

“…Calibration of the backscattered energy from different tissue regions is important. All methods including self-tuning fuzzy control must be able to cope with motion of the image features on which temperature estimates are based [19][20][21][22][23][24][25][26][27][28][29][30].…”

Model predictive control for MR-HIFU-mediated, uniform hyperthermia

“…This is exploited for closed-loop feedback to the HIFU transducer, allowing to deliver a well-defined thermal dose and to maintain stable temperatures [28]. HIFU was recognized and tested as a hyperthermia device early on [24,[29][30][31], but only MR-feedback enabled a stable hyperthermia over an extended period of time [32][33][34]. With a focus point of 2-3 mm in diameter and 5-7 mm in height, HIFU enables the local heating of tissue on the millimeter scale.…”

Clinical applications of focused ultrasound—The brain

“…Further insight into the focusing abilities, targeting and thermal absorption in the brain became available from focused ultrasound hyperthermia treatments performed starting in 1986 [22,23]. These treatments were performed through the skin after the removal of a portion of the skull bone; the skull being viewed as a barrier to therapeutic applications in the brain since the work of Lynn ( Figure 1).…”