Biomedical subjects

D A Sim

Publications and source records attributed to D A Sim.

23 records · Page 2Linked to original sources

PubMedDate not supplied

Results of a phase I regional hyperthermia device evaluation: microwave annular array versus radiofrequency induction coil.

The safety and efficacy of two devices in producing elevated temperatures in bulky deep tumours was evaluated in 11 patients with 12 tumours. Nine of 11 patients had pelvic tumours. Each patient was given a separate trial heating with the microwave annular phased microwave array system (APAS) and the radiofrequency concentric magnetic induction coil (MI), and evaluation was based upon paired comparison of power-limiting patient tolerance endpoints as well as intratumoural temperatures achieved. Toxicity was minimal with either device. On average, 66 per cent of intra-tumoural (IT) temperatures reached greater than 41 degrees C with the APAS, and 12 per cent of IT temperatures reached greater than 41 degrees C with the MI (P less than 0.001). Thirty-two per cent of IT temperatures were greater than 42 degrees C with the APAS, compared to 7 per cent with MI (P less than 0.001). Although the annular microwave array is more complex to use, it has a significantly higher likelihood of achieving temperatures in the therapeutic range near 42 degrees C in deep pelvic tumours than does the magnetic induction coil.

Aged↗

PubMedDate not supplied

Estimation of therapeutic gain in clinical trials involving hyperthermia and radiotherapy.

It is clear from discussions in this paper that phase III testing of hyperthermia in human patients must proceed in a cautious and stepwise fashion. Because of the risks of increasing late effects, either due to direct thermal damage or thermo-radiosensitization of normal tissues, it is not prudent to proceed with such testing in sites where there is a risk of excessive normal tissue heating. The correlations between temperature and prognosis in heated tumours implies that sites and techniques should be chosen where the chance of achieving relatively uniform heating are maximized. Methods of quality assurance are of equal importance and need to be carefully designed. Even then, retrospective analyses with temperature variations used as prognostic covariates are essential. Other factors, such as tumour volume and radiotherapy dose should be carefully controlled in experimental and control groups. Finally, protocol compliance is a real problem which will cause problems in interpretation of results, especially in studies designed to look at hyperthermic time-dose fractionation.

Animals↗

PubMedDate not supplied

The effect of hydralazine dose on blood perfusion changes during hyperthermia.

Experiments were performed to determine the dose-related effects of the intravenous administration of a vasodilator (hydralazine) on normal muscle blood perfusion during localized hyperthermia. Fourteen anaesthetized outbred canines were investigated, seven receiving the recommended dose level of 0.5 mg/kg and seven receiving one-quarter of that level. The changes in blood perfusion were estimated using two methods: calculation of an effective blood perfusion magnitude and the use of state and parameter estimation techniques. Both methods showed that the changes in blood perfusion induced by the hydralazine were significant, and that the differences between the results for the two drug doses were not significantly different. This suggests that low doses may be useful in humans, giving the same resultant blood perfusion increase but with a decreased patient risk relative to standard therapeutic doses of hydralazine. While the trends in the blood perfusion changes were the same for both calculation methods the effective perfusion method frequently yielded blood perfusion magnitudes significantly different from those obtained using the state and parameter estimation technique. The differences are postulated to be due to the fact that the effective perfusion values include conduction effects, thus overpredicting the amount of perfusion present. Thus, while the effective blood perfusion can be used as a qualitative indication of blood perfusion changes under certain conditions, we do not recommend its use as a quantitative measure of perfusion.

Animals↗

PubMedDate not supplied

Clinical evaluation of hyperthermia equipment: the University of Arizona Institutional Report for the NCI Hyperthermia Equipment Evaluation Contract.

Two-hundred and fifteen independent sites in 203 patients were treated with hyperthermia at the University of Arizona from 10/81 through 3/86 under the auspices of this contract. In the head and neck, a site dominated by superficial tumors, air-coupled and water-coupled microwave applicators yielded the best results. Similarly in the thorax, also dominated by superficial tumors, water-coupled microwave applicators were best. In the abdomen and pelvis, sites dominated by deep tumors, only interstitial radiofrequency (RF) heating, an invasive technique useful only in selected cases, was capable of consistently producing therapeutic temperatures. Toxicity appeared to be site-related, and treatment discomfort was especially common in abdominal and pelvic sites. In conclusion, while superficial sites were readily heated using propagative electromagnetic devices, these devices were ineffective and poorly tolerated at deeper sites. Effective deep hyperthermia was best produced with interstitial techniques, and further development of these techniques using RF electrodes, implantable microwave antennas and thermoregulating ferromagnetic seeds, as well as scanned, focussed-ultrasound techniques, holds promise for effective heating of deep visceral sites.

Clinical Trials as Topic↗

PubMedDate not supplied

Response of canine soft tissue sarcomas to radiation or radiation plus hyperthermia: a randomized phase II study.

Sixty-four dogs with spontaneous soft tissue sarcomas without evidence of metastases were stratified by tumour volume and randomized to receive graded doses of radiotherapy (XRT) alone or radiotherapy plus hyperthermia (HT). An improvement in duration of local control was achieved with the addition of hyperthermia as compared with XRT alone (Wilcoxon, p = 0.040; log rank, p = 0.064). Overall frequency of late complications was not different for the two treatment arms when comparing across equivalent XRT dose groups. Frequency of distant metastases after therapy completion was not significantly different for the two treatment arms at 1 year (7.4% for XRT versus 20% for HT plus XRT) or 2 years (11.5% for XRT versus 25% for HT plus XRT) post therapy. These results suggest that a therapeutic gain was achieved for this group of tumour-bearing animals. Uni- and multivariate analyses were performed to examine the potential for various factors to influence treatment outcome. Patient related variables included tumour stage, histologic subtype and grade and tumour site. Treatment related variables included total radiation dose and 15 descriptors of temperature distributions achieved during hyperthermia. When considering patient related factors, tumour histology, grade and location were important predictors of time to minimum volume, but only tumour location influenced time to tumour regrowth. When considering treatment related factors, radiation dose was not significantly correlated with time to minimum volume or time to local regrowth, but it was correlated with probability for late normal tissue damage in the XRT alone group (p = 0.005). For the hyperthermia treatments, 13 of 15 tumour temperature distribution descriptors were correlated with time to minimum volume, but none were correlated with time to local regrowth. These results suggest that caution should be used in interpreting the value of temperature distribution descriptors in predicting for long-term local control after hyperthermia and radiotherapy, based on analysis of short-term responses.

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