The response of mouse intestine to combined hyperthermia and radiation: the contribution of direct thermal damage in assessment of the thermal enhancement ratio

Two cases of fatal necrosis of the lesser pelvis in patients treated with combined radiotherapy and hyperthermia for cervical carcinoma

This study reports two cases of fatal necrosis of the lesser pelvis in patients with advanced cervical carcinoma, who had received combined radiotherapy and hyperthermia. The necrosis reached far from the high dose area, in one of the cases even outside the radiation portals. Both patients initially had treatment-related morbidity which responded well to surgical treatment. After a disease-free interval, a rapidly progressive necrosis developed. Necrosis to this extent after combined modality treatment has, to the authors' knowledge, not been described.

Localized hyperthermia and X-irradiation of murine jejunum in situ: a new method

In C3H mice, preparative surgery apposed a 15 mm length of jejunum to the peritoneal surface of the ventral abdominal wall. After the mice healed, manipulation of the abdominal wall made possible selective hyperthermic treatment and X-irradiation of the immobilized jejunal segment (IJS) while it remained within the peritoneal cavity and in continuity with the rest of the intestines. For hyperthermia, the ventral abdominal wall and attached IJS was flattened between two aluminium plates immersed in a standard water bath. The temperature at the mesenteric attachment of the IJS was within 0.5 degrees C of a 44 degrees C bath 100 s after immersion and within 0.3 degrees C at steady-state. Xenon-133 washout studies showed that the treatment technique did not compromise blood flow to the IJS. The preparative surgery left the IJS normally responsive to X-irradiation as determined by crypt microcolony assay. Hyperthermia treatment by itself at 44 degrees C for up to 20 min caused no loss of crypts or villi; however, adjuvant 5-15 min 44 degrees C hyperthermia displaced the X-ray crypt-survival curves towards lower doses without changing their slopes. Nevertheless, formal statistical analyses admitted both additive and multiplicative interpretations of the effects of X-irradiation and adjuvant hyperthermia on intestinal crypt survival. After adjuvant hyperthermia, the surviving crypts were preferentially clustered near the mesenteric attachment to a greater extent than was expected from the asymmetry of the heat dose.

Thermal enhancement of radiation damage in previously irradiated mouse intestine

The effects of prior irradiation (8 or 10 Gy of X rays) on the response of mouse jejunum to a test treatment of (a) hyperthermia (42.0 degrees C for 60 min), (b) X rays (8 or 10 Gy) or (c) combined hyperthermia and radiation were investigated at various times up to 7 months after the primary treatment. Tissue injury was quantified by crypt survival 4 days after the test treatment. Although tissue susceptibility to direct thermal injury was increased 10-15 days after irradiation, neither radiation sensitivity nor thermoradiosensitisation were significantly affected at any of the time intervals used. The results support the concept that there are different pathways for the in vivo expression of gross thermal damage and thermoradiosensitisation.

Time-temperature relationships for hyperthermal radiosensitisation in mouse intestine: influence of thermotolerance

Thermal enhancement of radiation injury to the crypt compartment of mouse small intestinal mucosa has been measured as a function of heating time for temperatures in the range 41.0-44.0 degrees C. All the hyperthermal treatments used were themselves subthreshold for gross tissue injury. With this limitation, thermoradiosensitisation increased linearly with duration of hyperthermia for temperatures in the range 42.3-44.0 degrees C. Using temperatures below 42.0 degrees C, there was a saturation in effect for treatments longer than approximately 40-90 min, possibly due to the development of thermotolerance. The thermoradiosensitisation isoeffect curve relating heating time with temperature was biphasic with the transition occurring between 41.8 and 42.0 degrees C. For temperatures above the transition, a 1 degree C change was equivalent to a factor of 2.6 in heating time; below the transition, a 1 degree C change was equivalent to a factor of 5.4. Time-temperature relationships for thermoradiosensitisation in other rodent tissues are reviewed and compared with the general relationships for direct thermal injury, previously derived from experimental studies. The results are discussed with relevance to the interpretation of in vivo thermal enhancement of radiation injury.

A study of the effects of prior heat treatment on the skin reaction of mouse feet after heat alone or combined with X-rays: influence of misonidazole

The skin of mouse feet was used to study the effects of hyperthermic treatment, either alone or combined with irradiation. The present experiments show that a priming heat treatment induces resistance both to a subsequent heat treatment and to a subsequent combined irradiation-heat treatment. The development of resistance to a combined irradiation-heat treatment after a priming heat treatment (30 min at 43 degrees C) was relatively slow (18-24 h) compared to development of resistance to a heat treatment without irradiation (6 h). Misonidazole, when administered prior to heat treatment only, did not influence the heat-induced skin reaction. However, when misonidazole was administered prior to combined irradiation-heat treatment, a slight but significant increase of the skin reaction was observed. Also, in combination with misonidazole resistance to combined treatment was observed by a priming heat treatment.

Formula to estimate the thermal enhancement ratio of a single simultaneous hyperthermia and radiation treatment

An experimental model composed of a C3H mammary carcinoma and its surrounding skin has been exposed to simultaneous radiation and hyperthermia given with different combinations of heating time and temperature. Based on the thermal enhancement ratio (TER) values obtained in the temperature range 41.5 to 43.5 degrees C, a linear relationship between TER and the heating time was achieved at each temperature. The slopes of the curves drawn at each temperature were found to have a log-linear relationship with the treatment temperature. With these relationships it was possible to make a formula expressing the TER as a function of treatment temperature and time. This formula gives a crude but probably acceptable estimate of the TER following a single simultaneous radiation and heat treatment. Although subject to several limitations, the formula represents an attempt to describe a heat dose concept for the radiosensitizing effect of hyperthermia. This may be useful to establish the tolerance level of a given radiation treatment when combined with hyperthermia.

Increased hyperthermal response of previously irradiated mouse intestine

The effect of prior irradiation (6-10 Gy of X rays) on the response of mouse jejunum to 43.0 degrees C hyperthermia was investigated. A dose of 6 Gy has no significant effect on the crypt loss measured after hyperthermia. However, intestine which had received 8-10 Gy showed increased susceptibility to subsequent thermal injury. Between approximately one and 2 weeks after 9 Gy, the thermal response of the intestine of CFLP mice increased such that, at maximal effect, heating pre-irradiated intestine at 43.0 degrees C was approximately equivalent to heating untreated intestine at 43.5 degrees C. The effect of prior irradiation was transient and appeared to have been "forgotten" after 2-3 months, a finding of particular relevance to the clinical situation. The results are discussed with reference to any radiation injury to intestine which might influence the expression of hyperthermal damage in situ.

A comparison of thermal enhancement ratios for fast neutron and x irradiation of two normal tissues in rodents

The effects of a hyperthermal treatment of one hour on radiation damage to baby rat cartilage and mouse intestine were compared for 250 kVp X irradiation and cyclotron-produced neutron irradiation (mean energy of about 7.5 MeV). Heat, in the range 41.0 degrees C-43.0 degrees C, caused no observable gross tissue injury when given alone. When heat was given immediately before radiation, the radiation damage was enhanced. There was no qualitative differences between response after fast neutrons and after X rays. Thermal enhancement ratios (TER) were similar for the two tissues and were not affected by the type of radiation used. Thus, the relative biological effectiveness (RBE) of fast neutrons compared with X rays was not markedly altered by combining radiation with hyperthermia.