Hyperthermia and the oxygen enhancement ratio for damage to baby rat cartilage

Local hyperthermia to canine prostate. A pilot study

Repeated treatments of localized deep microwave hyperthermia were given to a series of dogs by means of a 915 MHz, water-cooled skirt-type applicator. The applicator was inserted into the rectum and directed toward the prostate in order to heat it by means of the absorbed microwaves while keeping the rectal wall at a lower temperature by surface cooling of the applicator itself. Sessions were given for different lengths of time ranging between ninety minutes and five hours, during which the prostate temperature was kept at 42.5 degrees C (+/- 0.5 degrees C) or 44.5 degrees C (+/- 0.5 degrees C). Three-dimensional temperature distributions in the prostate were measured accurately and verified by a Luxtron Fluoroptic Unit. Temperatures were constantly monitored in the rectal wall and in the prostatic urethra. Thorough and systemic follow-up was done before, during, and after each treatment, and the observations are reported. Two interesting preliminary observations were made: (1) differential blood counts showed significantly monocytosis following the treatments and lasted for at least one week, and (2) values of creatinine phosphokinase (CPK) and serum glutamic oxaloacetic transaminase (SGOT) were found to rise irreversibly in those animals which were later found to have definite histopathologic evidence of localized necrotic damage.

The effect of hyperthermia on the early- and late-appearing mouse foot reactions and on radiation carcinogenesis: Part II. Effect on radiation carcinogenesis (thermal enhancement and oxygen enhancement)

The effect of hyperthermia on radiation carcinogenesis was investigated in the C3Hf/Sed mouse foot. The foot was irradiated under hypoxic conditions, in air, or under hyperbaric oxygen conditions to evaluate the oxygen effect. Hyperthermia at 43.5 degrees C for 45 min was given by immersing the animal foot into a constant temperature water bath. A malignant tumor in the irradiated foot was first observed congruent to 250 days after irradiation. Tumors developed in the irradiated area until day 850. RCD50, or 50% radiation carcinogenesis dose was the endpoint and was calculated based on the tumor incidence 650 days after irradiation. RCD50 following radiation given alone under hypoxic conditions was 66.3 (60.0-73.2) Gy, and the oxygen enhancement ratio (hypoxic/hyperbaric oxygen) was 3.0 (2.5-3.5). Radiation carcinogenesis was enhanced by hyperthermia given with a 20 min treatment interval with no significant alteration in the oxygen effect. Thermal enhancement was greatest when hyperthermia was given 20 min prior to irradiation (2.5 [2.2-2.9] under hypoxia). No thermal enhancement was observed when two treatments were given with a treatment interval of 2 days. The median time to develop a malignant tumor decreased with increasing radiation dose. This median time was shorter following combined hyperthermia and irradiation (423 days) than following radiation alone (504 days). Histological studies revealed that more than 80% of tumors were soft tissue sarcomas, and the most common tumor was fibrosarcoma. Squamous cell carcinoma was found in 7% of all tumors.

Hyperthermia in the treatment of prostate cancer

Hyperthermia-the sustained heating of tissues to temperatures of 42 degrees C to 43.5 degrees C--increasingly is being studied by scientists as a new tool to destroy cancer cells, either alone or in conjunction with other well established forms of treatment, such as radiotherapy and chemotherapy. Many studies on tissue cultures, on animals and also on humans, have established the fact that this new nonconventional adjuvant form of treatment is actually effective. Progress is being made in the development of the necessary technology for delivering the desired and controlled form of heat to the diseased site, while protecting the surrounding healthy tissues from irreversible damage. Initial clinical trials in this direction are very promising and seem to offer new avenues in the methods of treatment for cancer of the prostate.

Fractionated radiation and hyperthermia: experimental and clinical studies

The effect of fractionated radiation and hyperthermia was experimentally studied in a C3H mammary carcinoma and its surrounding skin. Simultaneous radiation and heat (42.5 C-60 minutes) with one or five fractions gave thermal enhancement ratios (TER) of approximately 2.5 in both tumor and surrounding skin, and no improved therapeutic effect was obtained. Five fractions of sequential treatment with heating four hours after radiation reduced the tumor TER to about 1.4, but when 72 hours were allowed between the fractions, no thermal enhancement of the skin was observed. Thus, an improved therapeutic ratio was observed. Clinically the combined treatment was studied in 12 patients with 49 metastases from malignant melanoma treated with different schedules of radiation and hyperthermia (approximately 43 C for 30 minutes). Simultaneous treatment with three fractions in eight days gave TER values in the skin between 1.2-1.4, but a similar effect was found in the tumor. Three fractions of sequential treatment in eight days did not produce any thermal enhancement of the skin response, but still presented an apparent gain of the tumor response, and so seemed to increase the therapeutic effect. Bases on these findings, the strategy for further clinical use of combined hyperthermia and radiation is discussed.

Effect of hyperthermia on the hypoxic fraction in an experimental mammary carcinoma in vivo

The influence of hyperthermia on the fraction of clonogenic hypoxic cells in a CaH mammary carcinoma was investigated using the TCD50 values for radiation treatment under normal or clamped conditions. A one-hour heat treatment at 41.5 and 42.5 degree C given four hours after radiation reduced the hypoxic fraction to 2.3 X 10(-1), 7.4 X 10(-3) and 6.5 X 10(-3) respectively, when compared with the content of hypoxic cells in non-heated tumours. The results indicate that moderate hyperthermia is able to destroy selectively a large proportion of the fraction of radioresistant hypoxic cells in a solid tumour. This effect is probably due to the increased heat sensitivity of cells in a chronically hypoxic and nutritionally deprived acidic environment.

Effect of misonidazole and hyperthermia on the radiosensitivity of a C3H mouse mammary carcinoma and its surrounding normal tissue

Both misonidazole (MISO) and hyperthermia are known to enhance the radiation response of hypoxic cells, and to be selectively cytotoxic against cells in a hypoxic and acidic environment. The ability of these conditions to modify the effect of irradiation and their individual relationship was studied in a C3H mammary carcinoma and its surrounding skin. Simultaneous treatment with MISO, hyperthermia and radiation increased the radiation effect, with enhancement ratios (ER) of up to about 15 (1 mg/g MISO and 43.5 degrees C for 60 min.). However, such treatment also caused a smaller hyperthermic radiosensitization of the normal tissue, so that the therapeutic ratio was only increased by a factor of about 3 compared to radiation alone. Simultaneous MISO and radiation followed by hyperthermia 4 h later gave a moderate enhancement, with ER up to 3 in the tumour, but with no enhancement of the normal tissue, so that there is a similar 3-fold increase in therapeutic gain. The mechanism by which MISO and hyperthermia enhanced the radiation response may be explained as an independent action of the hypoxic radiosensitization of MISO and the selective hyperthermic cytotoxicity against acidic and chronic hypoxic cells; simultaneous hyperthermia added a further heat-induced general radiosensitization. Surprisingly, no MISO cytotoxicity could be detected in this tumour system, with or without simultaneous hyperthermia. The results indicate that in the proper treatment schedule, MISO may be a valuable addition to a combined hyperthermia and radiation treatment.

Influence of hyperthermia on the oxygen enhancement ratio for x-rays, measured in vivo

The skin of mouse tail has been used to study the effect of hyperthermia on the oxygen enhancement ratio (OER). Heating was by immersion of a portion of the tail in hot water. Radiation was given either immediately before or after hyperthermia. The average skin reaction between 15 and 50 days after treatment was taken as the end-point. The OER in the absence of hyperthermia was 1.77, suggesting significant hypoxia of the skin. When hyperthermia was given after irradiation the measured value for the OER was not significantly different, but with prior hyperthermia the OER was increased to an average value of 2.3. This increase in OER is probably due to a transient increase in blood circulation following hyperthermia and causing improved tissue oxygenation during irradiation. As a consequence we would expect a greater thermal enhancement ratio for heat given before irradiation than afterwards, and this has frequently been observed with other normal tissues. There was no evidence that heat reduces OER, as has been reported by some authors on the basis of experiments performed on cells in vitro.