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Biomedical subjects

T C Cetas

Publications and source records attributed to T C Cetas.

At least 37 records · Page 2Linked to original sources
PubMed1984

Applications of bioheat transfer simulations in hyperthermia.

The applications of mathematical simulations of tissue temperature distributions in hyperthermia treatments are discussed in terms of four areas, comparative, prospective, concurrent, and retrospective thermal dosimetry. These four aspects of thermal dosimetry cover the range of hyperthermia applications of interest to clinicians, from comparative evaluation of competitive heating modalities to individual treatment planning, through feedback control during a treatment and, finally, to posttreatment therapy evaluation. Mathematical simulations of hyperthermia treatments can play a significant role in each of these areas.

Body Temperature↗
PubMed1984

Will thermometric tomography become practical for hyperthermia treatment monitoring?

Thermal tomography refers to the acquisition of detailed thermal information throughout a slice of the subject. Experimental temperature information of this nature to be obtained experimentally using some form of scanning mechanism is usually implied by the term, noninvasive thermometry. Desirable specifications for such a system are presented, and the degree to which the proposed methods are likely to achieve these are reviewed. Four major issues that must be resolved for any system to be useful clinically are: (a) will the system interfere with coupling the heating source to the patient and will the physician or technologist have access as well; (b) will its noise rejection be sufficient to operate in the presence of strong electromagnetic or ultrasonic heating fields; (c) will the spatial, temporal, and thermal resolution be sufficient to record important variations during treatments; and (d) will the parameter sensed be a function only of temperature or will it change as a consequence of physiological variations or therapeutic effects? It is concluded that noninvasive temperature scanning is unlikely to have a significant effect on thermal therapy for many years. Conversely, invasive thermometry coupled with numerical modeling is well along the way to becoming clinically useful.

Body Temperature↗
PubMed1984

Status and future developments in the physical aspects of hyperthermia.

The state of hyperthermia physics is reviewed. Major changes affecting the field are: (a) it is becoming far more sophisticated than just a few years ago, now that experts from many engineering and physical specialties are involved; (b) the ubiquitous computer is central to developments in data acquisition and analysis, treatment control, device comparison, treatment planning, and thermal dosimetry; and (c) entrepreneurial firms are arising to produce clinically engineered equipment. University and other research centers can concentrate their efforts on investigating new technologies up to the development of physical prototypes; they need no longer spend time on constructing complete clinical systems. At present, regional heating systems are unable to reliably induce therapeutic temperatures throughout the entire tumor volume. Interstitial techniques are able to accomplish this and so may make the greatest clinical impact in the near future. Invasive thermometry coupled with computerized data acquisition systems and numerical models appears to be a very promising approach to detailed thermal dosimetry. The tools for performing good clinical trials of hyperthermia are gradually becoming available.

Body Temperature↗
PubMed1984

Comparative evaluation of hyperthermia heating modalities. I. Numerical analysis of thermal dosimetry bracketing cases.

A method for comparing the relative abilities of different hyperthermia heating modalities to properly heat tumors has been developed using solutions of the bio-heat transfer equation. A single measure, the range of absorbed powers that gives acceptable tissue temperature distributions, is used to characterize the ability of a given heating technique to heat a given tumor. An acceptable tissue temperature distribution is one for which (a) the temperatures in the coolest regions of the tumor are above a minimum therapeutic value, (b) the temperatures in the hottest regions of the tumor do not exceed a maximum clinically acceptable value, and (c) the normal tissue temperatures do not exceed maximum clinically acceptable levels. This measure can be interpreted directly in clinical terms as the range of power settings on the power indicator of a heating device for which acceptable tumor heatings will occur. This paper describes the basis of the method and investigates the role of tumor blood perfusion patterns in determining the size of the acceptable power range. Three tumor perfusion patterns are investigated: uniform tumor perfusion, a concentric annulli perfusion model in which the tumor consists of a necrotic core surrounded by two concentric layers of increased perfusion, and a random perfusion distribution model. The results show that, in general, the uniform and annular perfusion models serve as bracketing case patterns. That is, they give acceptable power range values that are upper and lower limits of the acceptable power ranges obtained for the random perfusion patterns. The method is applied to heating patterns that simulate those obtained from a variety of different available heating techniques, and it is found to be valid for all cases studied. The role of normal tissue limiting conditions is also investigated.

Humans↗
PubMed1984

Comparative evaluation of hyperthermia heating modalities. II. Application of the acceptable power range technique.

The acceptable power range technique previously described in a companion paper [R. B. Roemer, T. C. Cetas, J. R. Oleson, S. Halac, and A. Y. Matloubieh, Radiat. Res. 100, 450-472 (1984)] is applied to two heating modalities to demonstrate its application to simulated clinical situations. Comparisons of the abilities of the different modalities to heat given tumors are made using the relative sizes of the acceptable power ranges obtained for each modality. Similar comparisons are also possible for determining the efficacy of physiological manipulations and adjustments in power deposition patterns for a given heating modality. Predictions of the ability of modalities and configurations to properly heat tumors are made using the bracketing nature of the uniform and annular tumor perfusion models. These comparisons and predictions are possible because a single measure of the ability of any heating technique to heat an arbitrary tumor in any location is utilized (the size of the acceptable power range). While relatively simple models are presently utilized, this approach can be extended to take into account a host of physical and biological conditions that model the patient-device interaction to an arbitrarily high degree of detail. These refinements will be based on extended clinical and experimental data, particularly as tumor and normal tissue blood perfusion characteristics either become better known in general cases or can be specified for each real tumor. The applications of this approach should be far-reaching and complementary to clinical hyperthermia, especially as further model refinements are incorporated. Additional data are presented which reinforce the bracketing nature of the uniform and annular tumor perfusion models presented in the companion paper.

Humans↗
PubMed1983

Magnetic induction heating of tissue: numerical evaluation of tumor temperature distributions.

A one dimensional (radial) numerical model based on the bioheat transfer equation has been developed and applied to the abdomen and pelvis heated by a concentric magnetic induction electrode. This model consists of four normal tissue regions: viscera, muscle, fat and skin. Each region is assigned thermal properties characteristic of that region and power deposition values consistent with those for this mode of heating. Tumors of 2, 4 and 7 cm thicknesses are positioned in five different radial locations ranging from the central axis to the skin surface. Two blood perfusion models of the tumor are considered: the uniformly perfused model and an annular model. Tumor temperature distributions are considered acceptable if the average tumor temperature plus and minus two standard deviations lie between 42 degrees C and 60 degrees C. To stimulate practical clinical restrictions, muscle and fat temperatures are not allowed to exceed 44 degrees C, significant portions of the viscera (except for a 1 cm thick band) are not allowed to exceed 42 degrees C, and the total absorbed power required to maintain steady state cannot exceed one kilowatt. Over 100 possible cases are presented in a compact form. A conclusion drawn from this study is that with few exceptions, only small tumors in the muscle annulus are heated adequately with this modality. Large tumors will have significant unheated portions if the specified limitations are not exceeded. While this heating modality can raise the necrotic core of a tumor to high temperatures, it cannot adequately heat well perfused regions of a deep seated tumor. These conclusions are borne out clinically and are discussed in a companion paper.

Diathermy↗
PubMed1983

Uniform regional heating of the lower trunk: numerical evaluation of tumor temperature distributions.

The temperature distributions in deep seated tumors resulting from uniform heating of the abdominal and pelvic regions of the trunk are predicted from a one dimensional numerical solution of the bio-heat transfer equation. The effect of tumor size and location are investigated for two tumor perfusion models: uniform perfusion and a concentric annulus perfusion model. Tumor temperature distributions are considered acceptable if the range of temperatures in the tumor lie between 42 degrees C and 60 degrees C. This range of tumor temperatures is defined as Tave +/- 2 sigma where sigma is the population standard deviation of tumor temperatures from the average computed at the nodal points in the finite difference array. To simulate practical clinical restrictions, muscle and fat temperatures are not allowed to exceed 44 degrees C, significant portions of the viscera are not allowed to exceed 42 degrees C, and the total absorbed power required to maintain steady state cannot exceed two kilowatts. Over 100 possible cases are presented in a compact form. From this study it appears that heating systems with power deposition patterns approximately uniform are promising for heating deep-seated tumors. Small, detectable tumors (approximately 2 cm in size) are adequately heated for a wider range of conditions than are larger tumors. Excessively high temperatures in deep-seated, normal tissue could be a significant limitation for this technique.

Abdominal Neoplasms↗
PubMed1983

Scalp hypothermia: a comparison of ice packs and the Kold Kap in the prevention of doxorubicin-induced alopecia.

Two methods of scalp hypothermia were compared in preventing alopecia, a side effect of doxorubicin chemotherapy that has a significant psychologic impact on the patient. Thirty-three patients received scalp ice packs consisting of crushed ice in plastic bags. Twenty-nine patients received Kold Kap, a device that produces chilling via an endothermic reaction. Scalp hypothermia was applied for 5-10 min before the doxorubicin bolus and left in place for 30-40 min afterward. The percent of hair loss was rated at each visit and photographs were used to further quantitate any hair loss. Sixty-three percent of Kold Kap and 56% of ice pack patients had good or better protection and did not require wigs. Excellent protection (less than 25% loss) was provided for 51% of Kold Kap and 33% of ice pack patients. Similar protection was provided to Kold Kap patients regardless of dose, while ice pack patients received significantly better protection if their doxorubicin doses were less than 50 mg. Scalp hypothermia is an effective method of preventing doxorubicin-induced alopecia.

Alopecia↗
PubMed1983

Hyperthermia by magnetic induction: experimental and theoretical results for coaxial coil pairs.

High-frequency magnetic induction for producing elevated temperatures in human tumors can be accomplished with several electrode arrangements. We describe the physical characteristics of a coaxial pair of electrodes or current loops placed on either side of the body. This electrode arrangement can improve the depth of power deposition within the body relative to that obtained with an electrode circumferentially encircling the body or a single surface applicator ("pancake coil"). We report results of measured and calculated magnetic field distributions and power density distributions obtained with a coaxial pair. The effect of varying load geometry upon the power density distribution was shown to be significant in several static phantom experiments. Electrode geometry was also important, as shown by calculations of power deposition as a function of electrode diameter in a simple model of body tissue conductivities. The power density was found to diminish at given depths as the electrode diameter decreased. Finally, values of magnetic fields were measured during treatment of human subjects with a coaxial electrode pair and were found to vary significantly from subject to subject. This resulted from variation in the geometry and electrical characteristics of tissues among subjects, and indicates the difficulty of formulating a standard accurate model for use with this magnetic induction technique.

Diathermy↗
PubMed1982

Clinical hyperthermia: results of a phase I trial employing hyperthermia alone or in combination with external beam or interstitial radiotherapy.

Forty-three patients with advanced, locally accessible neoplasms were treated in a Phase I clinical trial employing hyperthermia alone or hyperthermia combined with either high-dose-rate external beam or low-dose-rate interstitial radiotherapy (interstitial thermoradiography). All patients had failed previous conventional therapeutic attempts, including various combinations of surgery, chemotherapy and radiation therapy. Many had received tolerance or near tolerance levels of prior radiation that restricted dose prescriptions in this trial to subcurative values. A number of tumors with different histologies were treated, including squamous cell carcinoma (14), adenocarcinoma (14), melanoma (8), malignant fibrous histiocytoma (2), and sarcoma (5). The response evaluation criteria used included no response (NR--less than 50% decrease in tumor volume), partial response (PR--50% less than or equal to tumor volume reduction less than 100%) and complete response (CR--complete tumor disappearance). For all tumor types, hyperthermia therapy alone resulted in a total response rate of 45% (27% PR, 18% CR). Hyperthermia combined with high-dose-rate external beam radiotherapy yielded a total response rate of 80% (53% PR, 27% CR). Seventeen patients treated with interstitial thermoradiography displayed a 100% total response rate (29% PR, 71% CR). By tumor histologies for all treatment groups, total response rates have ranged from 50% to 79% for all types except melanoma, which has shown a 100% (8/8) response rate to date. Response durations have varied from one to 24 months. Twelve of the 43 patients remain alive; three have no evidence of disease (NED) while nine have either stable local disease or are NED in the treated volumes but have metastatic disease. Complications have been minimal and have included one third-degree burn and three second-degree burns from fringing RF fields, one vaginal-rectal fistula, a superficial focal soft tissue necrosis, and some minor blistering. The results of this Phase I trial demonstrate that hyperthermia alone or combined with radiation can be safely applied in the treatment of malignant disease. Most importantly, the data suggest that hyperthermia, especially when combined with interstitial thermoradiography, can yield remarkable results in the eradication of local cancers.

Adenocarcinoma↗
PubMed1982

Interstitial thermoradiotherapy.

The results of a phase I clinical trial in which heat was combined with interstitial (low dose rate) radiation are described with emphasis on response and technical and physical aspects of heating. We treated 25 patients (27 lesions) using interstitial implants to locally recurrent, accessible tumors heated by radiofrequency currents to 43 degrees -45 degrees C for 30 minutes, with needle guides as electrodes. They were subsequently irradiated with either 192Ir or 226Ra. All patients had failed previous conventional treatments including surgery, chemotherapy, and, in most, near tolerance doses of irradiation. In all but one, a single hyperthermic treatment was given and the average dose of low dose irradiation was under 3,000 rad over 60 hours. No patient failed to respond, 63% achieved a complete disappearance of tumor in the treated volume, and 37% had partial response (50% less than volume reduction less than 100%). Duration of response was from 2 to 30 months, and no patient showed regrowth at the site treated. Normal tissue complications were minimal. Interstitial thermoradiotherapy is both a safe and an effective means of treatment in advanced or recurrent accessible disease.

Adenocarcinoma↗