The therapeutic advantage of combined heat and X rays on a mouse fibrosarcoma

Evaluation of Thermal Properties of Ferromagnetic Core for Treatment of Solid Tumors by Electromagnetic Induction Hyperthermia

Background

Electromagnetic induction hyperthermia is a promising method to treat the deep-seated tumors such as brain and prostatic tumors. This technique is performed using the induction of electromagnetic waves in the ferromagnetic cores implanted at the solid tumor.

Objective

This study aims at determining the conditions of the optimal thermal distribution in the different frequencies before performing the in vitro cellular study.

Material and Methods

In this experimental study, the i-Cu alloy (70.4-29.6; wt%) was prepared and characterized and then the parameters, affecting the amount of induction heating in the ferromagnetic core, were investigated. Self-regulating cores in 1, 3, 6, and 9 arrangements in the water phantom with a volume of 2 cm3 were used as a replacement for solid tumor.

Results

Inductively Coupled Plasma (ICP) analysis and Energy Dispersive X-ray Spectroscopy (EDS) show the uniformity of the alloy after 4 times remeling by vacuum arc remelting furnace. The Vibrating Sample Magnetometer (VSM) shows that the Curie temperature (TC) of the ferromagnetic core is less than 50 °C. Temperature profile with a frequency of 100-400 kHz for 30 min, was extracted by infrared imaging camera, indicating the increase temperature in the range of 42 °C to 46 °C.

Conclusion

The optimum conditions with used hyperthermia system are supplied in the frequency of 100 kHz, 200 kHz and 400 kHz with 6, 3 and 1 seeds, respectively. It is also possible to induce a temperature up to 50 °C by increasing the number of seeds at a constant frequency and power, or by increasing the applied frequency at a constant number of seeds.

Management of the Cavity After Removal of Giant Cell Tumor of the Bone

Purpose: To find out the most appropriate management scheme through the analysis and comparison of different inactivation methods and filling materials. Method: A systematic literature search was performed using the terms, anhydrous ethanol, phenol, hypertonic saline, cryotherapy, thermal therapy, bone reconstruction, GCTB, and etc., Selected articles were studied and summarized. The mechanism, clinical effects, and influence on bone repair of various methods are presented. Recent developments and perspectives are also demonstrated. Recent Findings: Compared to curettage alone, management of the residual cavity can effectively reduce the recurrence of giant cell tumours of bone. It is a complex and multidisciplinary process that includes three steps: local control, cavity filling, and osteogenic induction. In terms of local control, High-speed burring can enlarge the area of curettage but may cause the spread and planting of tumour tissues. Among the inactivation methods, Anhydrous ethanol, and hyperthermia therapy are relatively safe and efficient. The combination of the two may achieve a better inactivation effect. When inactivating the cavity, we need to adjust the approach according to the invasion of the tumour. Filling materials and bone repair should also be considered in management.

Measurement and analysis of the impact of time-interval, temperature and radiation dose on tumour cell survival and its application in thermoradiotherapy plan evaluation

PURPOSE

Biological modelling of thermoradiotherapy may further improve patient selection and treatment plan optimisation, but requires a model that describes the biological effect as a function of variables that affect treatment outcome (e.g. temperature, radiation dose). This study aimed to establish such a model and its parameters. Additionally, a clinical example was presented to illustrate the application.

METHODS

Cell survival assays were performed at various combinations of radiation dose (0-8 Gy), temperature (37-42 °C), time interval (0-4 h) and treatment sequence (radiotherapy before/after hyperthermia) for two cervical cancer cell lines (SiHa and HeLa). An extended linear-quadratic model was fitted to the data using maximum likelihood estimation. As an example application, a thermoradiotherapy plan (23 × 2 Gy + weekly hyperthermia) was compared with a radiotherapy-only plan (23 × 2 Gy) for a cervical cancer patient. The equivalent uniform radiation dose (EUD) in the tumour, including confidence intervals, was estimated using the SiHa parameters. Additionally, the difference in tumour control probability (TCP) was estimated.

RESULTS

Our model described the dependency of cell survival on dose, temperature and time interval well for both SiHa and HeLa data (R²=0.90 and R²=0.91, respectively), making it suitable for biological modelling. In the patient example, the thermoradiotherapy plan showed an increase in EUD of 9.8 Gy that was robust (95% CI: 7.7-14.3 Gy) against propagation of the uncertainty in radiobiological parameters. This corresponded to a 20% (95% CI: 15-29%) increase in TCP.

CONCLUSIONS

This study presents a model that describes the cell survival as a function of radiation dose, temperature and time interval, which is essential for biological modelling of thermoradiotherapy treatments.

3D radiobiological evaluation of combined radiotherapy and hyperthermia treatments

PURPOSE

Currently, clinical decisions regarding thermoradiotherapy treatments are based on clinical experience. Quantification of the radiosensitising effect of hyperthermia allows comparison of different treatment strategies, and can support clinical decision-making regarding the optimal treatment. The software presented here enables biological evaluation of thermoradiotherapy plans through calculation of equivalent 3D dose distributions.

METHODS

Our in-house developed software (X-Term) uses an extended version of the linear-quadratic model to calculate equivalent radiation dose, i.e. the radiation dose yielding the same effect as the thermoradiotherapy treatment. Separate sets of model parameters can be assigned to each delineated structure, allowing tissue specific modelling of hyperthermic radiosensitisation. After calculation, the equivalent radiation dose can be evaluated according to conventional radiotherapy planning criteria. The procedure is illustrated using two realistic examples. First, for a previously irradiated patient, normal tissue dose for a radiotherapy and thermoradiotherapy plan (with equal predicted tumour control) is compared. Second, tumour control probability (TCP) is assessed for two (otherwise identical) thermoradiotherapy schedules with different time intervals between radiotherapy and hyperthermia.

RESULTS

The examples demonstrate that our software can be used for individualised treatment decisions (first example) and treatment optimisation (second example) in thermoradiotherapy. In the first example, clinically acceptable doses to the bowel were exceeded for the conventional plan, and a substantial reduction of this excess was predicted for the thermoradiotherapy plan. In the second example, the thermoradiotherapy schedule with long time interval was shown to result in a substantially lower TCP.

CONCLUSIONS

Using biological modelling, our software can facilitate the evaluation of thermoradiotherapy plans and support individualised treatment decisions.

Amelioration of radiation-induced fibrosis: inhibition of transforming growth factor-beta signaling by halofuginone

Radiation-induced fibrosis is an untoward effect of high dose therapeutic and inadvertent exposure to ionizing radiation. Transforming growth factor-beta (TGF-beta) has been proposed to be critical in tissue repair mechanisms resulting from radiation injury. Previously, we showed that interruption of TGF-beta signaling by deletion of Smad3 results in resistance to radiation-induced injury. In the current study, a small molecular weight molecule, halofuginone (100 nm), is demonstrated by reporter assays to inhibit the TGF-beta signaling pathway, by Northern blotting to elevate inhibitory Smad7 expression within 15 min, and by Western blotting to inhibit formation of phospho-Smad2 and phospho-Smad3 and to decrease cytosolic and membrane TGF-beta type II receptor (TbetaRII). Attenuation of TbetaRII levels was noted as early as 1 h and down-regulation persisted for 24 h. Halofuginone blocked TGF-beta-induced delocalization of tight junction ZO-1, a marker of epidermal mesenchymal transition, in NMuMg mammary epithelial cells and suggest halofuginone may have in vivo anti-fibrogenesis characteristics. After documenting the in vitro cellular effects, halofuginone (intraperitoneum injection of 1, 2.5, or 5 microg/mouse/day) efficacy was assessed using ionizing radiation-induced (single dose, 35 or 45 Gy) hind leg contraction in C3H/Hen mice. Halofuginone treatment alone exerted no toxicity but significantly lessened radiation-induced fibrosis. The effectiveness of radiation treatment (2 gray/day for 5 days) of squamous cell carcinoma (SCC) tumors grown in C3H/Hen was not affected by halofuginone. The results detail the molecular effects of halofuginone on the TGF-beta signal pathway and show that halofuginone may lessen radiation-induced fibrosis in humans.

Heating the patient: a promising approach?

There is a clear rationale for using hyperthermia in cancer treatment. Treatment at temperatures between 40 and 44 degrees C is cytotoxic for cells in an environment with a low pO(2) and low pH, conditions that are found specifically within tumour tissue, due to insufficient blood perfusion. Under such conditions radiotherapy is less effective, and systemically applied cytotoxic agents will reach such areas in lower concentrations than in well perfused areas. Therefore, the addition of hyperthermia to radiotherapy or chemotherapy will result in at least an additive effect. Furthermore, the effects of both radiotherapy and many drugs are enhanced at an increased temperature. Hyperthermia can be applied by several methods: local hyperthermia by external or internal energy sources, regional hyperthermia by perfusion of organs or limbs, or by irrigation of body cavities, and whole body hyperthermia. The use of hyperthermia alone has resulted in complete overall response rates of 13%. The clinical value of hyperthermia in addition to other treatment modalities has been shown in randomised trials. Significant improvement in clinical outcome has been demonstrated for tumours of the head and neck, breast, brain, bladder, cervix, rectum, lung, oesophagus, vulva and vagina, and also for melanoma. Additional hyperthermia resulted in remarkably higher (complete) response rates, accompanied by improved local tumour control rates, better palliative effects and/or better overall survival rates. Generally, when combined with radiotherapy, no increase in radiation toxicity could be demonstrated. Whether toxicity from chemotherapy is enhanced depends on sequence of the two modalities, and on which tissues are heated. Toxicity from hyperthermia cannot always be avoided, but is usually of limited clinical relevance. Recent developments include improvements in heating techniques and thermometry, development of hyperthermia treatment planning models, studies on heat shock proteins and an effect on anti-cancer immune responses, drug targeting to tumours, bone marrow purging, combination with drugs targeting tumour vasculature, and the role of hyperthermia in gene therapy. The clinical results achieved to date have confirmed the expectations raised by results from experimental studies. These findings justify using hyperthermia as part of standard treatment in tumour sites for which its efficacy has been proven and, furthermore, to initiate new studies with other tumours. Hyperthermia is certainly a promising approach and deserves more attention than it has received until now.

A moderate elevation of blood glucose level increases the effectiveness of thermoradiotherapy in a rat tumor model II. Improved tumor control at clinically achievable temperatures

PURPOSE

To assess the therapeutic gain (at the TCD(50) level) that can be obtained by boosting thermoradiotherapy with intravenous glucose infusion at different temperatures. This completes our series of studies to determine the optimal conditions and the effectiveness of glucose administration at clinically achievable glucose levels and treatment temperatures.

METHODS AND MATERIALS

Subcutaneous rat rhabdomyosarcoma BA1112 was irradiated with graded single doses of 300-kV X-rays (dose range 0-60 Gy). Fifteen minutes after irradiation, a 100-min intravenous infusion was started, consisting of either glucose (20% solution, 2.4-3 g/kg/h) or saline as a control. Then heat was applied to the tumors at 42 degrees C or 43 degrees C (water bath) during a subsequent 100-min period of infusion. Tumor control was scored as the absence of palpable growth at 100 days after treatment.

RESULTS

Glucose infusion enhanced tumor control independent of temperature in the range 42-43 degrees C. At 42 degrees C, the TCD(50) for X-irradiation decreased by 5.9 Gy (SEM 1.8 Gy), from 41.6 (1.6) to 35.7 (1.5) Gy, and at 43 degrees C from 33.3 (1.6) to 27.3 (1.5) Gy, representing a glucose enhancement ratio of approximately 1.2. At doses corresponding to the TCD(50) at either 42 or 43 degrees C, the addition of glucose increased tumor control from 50% to 70%. An enhancement ratio of 2.1 was found for the combination of irradiation, glucose infusion, and heating at 43 degrees C, with respect to irradiation alone (TCD(50) 56.3 Gy, reanalyzed earlier data). The contribution of combined heat and glucose to tumor control represented an additive effect, probably on the hypoxic cell population.

CONCLUSION

Moderate glucose administration (blood concentration 300 mg/100 mL) sizably improves experimental tumor control after combined X-irradiation and hyperthermia under clinically feasible conditions. Clinical treatment should benefit from this additional modality, in particular if unsatisfactory local control rates are due to insufficient heating. The therapeutic gain has to be evaluated further in clinical studies.

Hyperthermia induces apoptosis in malignant fibrous histiocytoma cells in vitro

The effect of mild hyperthermia on a cultured rat malignant fibrous histiocytoma (MFH) cell line, MFH-2NR, was investigated. MFH cells in log-phase (growing phase) were heated at 41 degrees-44 degrees C for 1 hr. Hyperthermic treatment at 41 degrees C did not substantially affect cell proliferation and treatment at 44 degrees C caused necrosis. After hypothermic treatment at 42 degrees or 43 degrees C, proliferation of MFH cells was arrested and morphological changes characteristic of apoptosis, cell shrinkage accompanying apoptotic bodies and chromatin condensation, became apparent. Hyperthermia-induced apoptosis was further confirmed by terminal deoxynucleotidyl transferase staining and a ladder pattern on agarose gel electrophoresis. Flow cytometric analysis indicated that the population in the G1 phase of the cell cycle significantly decreased with a concomitant increase in apoptotic cells, indicating that apoptosis might occur mainly in the G1 phase population.

Effect of hyperthermia on the central nervous system: a review

Experimental data show that nervous tissue is sensitive to heat. Animal data indicate that the maximum tolerated heat dose after local hyperthermia of the central nervous system (CNS) lies in the range of 40-60 min at 42-42 x 5 degrees C or 10-30 min at 43 degrees C. No conclusions concerning the heat sensitivity of nervous tissue can be derived from clinical studies using localized hyperthermia. The choice whether or not to exceed the critical heat dose, as derived from laboratory studies, in clinical practice is very much dependent on the clinical situation such as the anatomical site and volume of the tissue involved, and prior therapy. Data on clinical application of whole body hyperthermia (WBH) show that nervous tissue can withstand a slightly higher heat dose than after localized heating, which might be the result of developing thermal resistance during treatment. Expression of thermotolerance was observed in the spinal cord of laboratory animals. After WBH in man at a maximum between 40 and 43 degrees C for 6 h-30 min CNS complications were reported, but other complications seemed to be more life-threatening. Most studies indicate that impairment of the CNS after WBH was not due to direct heat injury to the brain or spinal cord, but was secondary as a result of physiological changes. Heat, at least if applied shortly after X-rays, enhances the response of nervous tissue to radiation. Neurotoxicity of chemotherapeutic drugs does not seem to be a limiting complication in hyperthermia if combined with chemotherapy, but only few data are available. The limited clinical experience shows that safe hyperthermic treatment of CNS malignancies or tumours located close to the CNS seems feasible under appropriate technical conditions with adequate thermometry and taking the sensitivity of the surrounding normal nervous tissue into account.

Induction of tolerance to hypothermia and hyperthermia by a common mechanism in mammalian cells

Pretreatment by hypothermic (25 degrees C) cycling (PHC) of attached exponential-phase V79 Chinese hamster cells by Method 4 (24 hr at 25 degrees C + 1.5 hr at 37 degrees C + 24 hr at 25 degrees C + trypsin + 3 hr at 37 degrees C) or by Method 3 (48 hr at 25 degrees C + trypsin + 3 hr at 37 degrees C) make mammalian V79 cells significantly more resistant to 43 degrees C hyperthermia. There is no significant difference in the 43 degrees C curves whether Method 3 or 4 is used for pre-exposure. If pre-exposure at 15 or 10 degrees C, the resistance to hyperthermia is significantly reduced. PHC by Method 4 significantly increases survival of cells exposed to 5 degrees C and, to a lesser extent, to 10 degrees C. The increase in hyper- and hypothermic survival after PHC cannot be accounted for by changes in cell cycle distribution. Heat-shock protein synthesis is not induced by PHC; hence, protection does not result from newly synthesized proteins. When cells are made tolerant to hyperthermia by a pretreatment in 2% DMSO for 24 hr at 37 degrees C (Method 8), the cells are not more resistant to subsequent exposures to hypothermia, either at 5 or 10 degrees C. The results imply that there may be two mechanisms of inducing resistance to hyperthermia, only one of which also confers resistance to hypothermia.

Lethal interaction between heat and methylene blue in Escherichia coli

Hyperthermia treatment is shown to act synergistically with methylene blue (MB), from the end point of lethality in Gram-negative Escherichia coli bacteria. That this lethality is correlated to the damage produced in DNA by the dye is deduced from the fact that bacteria differing in capacity for repair are almost equally sensitive to heat, but differ considerably in sensitivity to concomitant heat and dye treatment. It is demonstrated that the damage is repairable by the excision-repair system. The role of temperature seems to be that of facilitating the incorporation of the dye, which enables the latter to intercalate into the DNA. Ability of the outer membrane of E. coli AB1157 bacteria to act as a barrier to the penetration of MB remains almost intact up to 46 degrees C, but above this temperature it seems to disrupt abruptly (but reversibly), leading to inactivation of the cells by the dye. Since hyperthermia is in current use for the treatment of cancer, it is suggested that if this synergism also exists in mammalian cells, MB could eventually be used independently of its photodynamic action as an adjuvant in cancer therapy.

Enhancement by hyperthermia of the 'early delayed' and 'late delayed' radiation response of the rat cervical spinal cord

The cervical spinal cord (C5-T5) of female Wistar WU rats was irradiated with 250 kV X-rays (15-32 Gy). Heat was applied at approximately the same site 7 +/- 1 min after X-rays. 'Early delayed' paralysis of the forelegs was observed 5-10 months after treatment. The ED50 (+/- SE) after single-dose irradiation alone was 25.8 +/- 0.4 Gy. 'Late delayed' paralysis and paresis were observed 11-21 months after irradiation with an ED50 (X-rays alone) of 22.7 +/- 0.6 Gy. The data for late paralysis, late paresis and minor neurological symptoms were pooled resulting in an ED50 (+/- SE) of 20.6 +/- 0.7 Gy. Hyperthermia enhanced the radiation response. Thermal enhancement ratios (TER) in the 'early delayed' response after a 30 min treatment with 41.1 +/- 0.4 degrees C 42.1 +/- 0.4 degrees C and 42.9 +/- 0.4 degrees C were 1.07 +/- 0.08, 1.17 +/- 0.08 and 1.12 +/- 0.04, respectively. For the 'late delayed' radiation response concerning paralysis and paresis the TER after 30 min at 41.1 degrees C and 42.1 degrees C were 1.25 +/- 0.10 and 1.31 +/- 0.07, respectively. The latent period for paralysis was not significantly affected. Pathological examination of the spinal cord after combined treatment of X-rays and hyperthermia showed focal demyelination with white matter necrosis and vascular injury in animals as an indication of 'early delayed' and 'late delayed' paralysis, respectively. This was not different from histopathological changes observed after irradiation alone.

Reduced thermal sensitivity of the vasculature in a slowly growing tumour

The thermal sensitivity of a slowly growing murine mammary carcinoma has been studied, and correlated with several vascular parameters. This tumour, CaRH, had previously been shown to be particularly resistant to hyperthermia when applied as 1 h immersion in a 42.8 degrees C water bath, with or without added X-rays. In the present study water bath temperatures of 43, 44 and 45 degrees C were used as well as a more complex system of water bath plus radiofrequency currents which produced a uniform intratumour temperature of 43 degrees C. Following treatment the tumour blood volume and relative capillary perfusion were estimated using radioactive tracer techniques. Only the treatments which gave at least 60 per cent reduction in blood perfusion yielded significant growth delays or thermal radiosensitization. These data have been compared with values for six other murine tumours. If, instead of comparing the exposure temperature, we compare the blood flow reduction, it is seen that all of the tumours are similar in their thermosensitivity. A higher temperature may be needed to cause vascular shutdown in more slowly growing tumours, but it is achieved with an intratumour temperature of 43 degrees C for 1 h. This may correlate with endothelial cell proliferation rates, which are similar in CaRH to the values measured in human tumours. The more rapid vascular expansion of the fast-growing tumours may result in a more fragile and thermosensitive capillary network. The hypoxic fraction, which is a measure of vascular inadequacy, also correlates with thermal sensitivity.

Microwave-induced hyperthermia and radiotherapy in human superficial tumours: clinical results with a comparative study of combined treatment versus radiotherapy alone

Eighty-five evaluable superficial recurrent malignant tumours, mainly adenocarcinomas (78 per cent), in 38 patients were treated with either combined local hyperthermia (41-45 degrees C for four sessions) and low dose radiotherapy (30.0 Gy) or the same low dose radiotherapy alone. The treatment was given for two weeks. Hyperthermia was induced externally with 2450 MHz or 915 MHz microwaves. Totally 57 tumours were given combined treatment with a complete and partial response rate of 46 and 30 per cent, respectively (duration 1-38 months). In 18 patients with 2-10 superficial tumours each, 56 tumours were used in a comparative study, comparing the effect of combined hyperthermia and low dose radiotherapy versus the same low dose radiotherapy alone, the patients acting as their own controls. The total response rates were 89 and 50 per cent, respectively, in the two treatment modality groups. The difference in response rates is significant (p = 0.0039) in favour of the combined treatment, and this is also found when comparing complete remissions only (p = 0.0027). Local pain and normal tissue reactions presented problems during and after 2450 MHz microwave-induced hyperthermia treatment, performed without a coupling water bag system. Introduction of 915 MHz microwave-induced hyperthermia with a coupling deionized water bag system and refinement of microwave applicators, as well as the temperature control system considerably reduced these problems.

Combined effects of hyperthermia, bleomycin, and X rays on Ehrlich ascites tumor

The combined effects of water-bath hyperthermia at 42.5 degrees C for 30 min, 1/10 LD50 Bleomycin iv, and 200 rad x irradiation were studied in DDD strain male mice with Ehrlich ascites tumor. The objective was to acquire data on the optimum regimen for a combined administration of these three modalities. The treatments were given 10 days after the inoculation of 2 X 10(6) of the cells into the right hind limb. Concomitant application of the three modalities led to an 80% regression. A single modality produced no significant effect and a 30-50% regression occurred when only two modalities were combined. To assess the influence of timing and sequence, hyperthermia was applied at 1, 2, 4, and 6 hr before, after, or simultaneously with the combination of Bleomycin and 200 rad X ray. A significant effect was obtained in the case of concomitant application of the three and hyperthermia was effective when applied within 2 hr before or after administration of Bleomycin plus irradiation. This enhancement disappeared at 4-hr intervals.

Thermochemotherapy (combined cyclophosphamide and hyperthermia) with or without hyperglycemia as an adjuvant to radiotherapy

Our previous study demonstrated the presence of a thermochemotherapy-resistant cell fraction in a tumor. The present study investigated whether thermochemotherapy-resistant cells are radioresistant and whether thermochemotherapy changes the size of hypoxic cell fraction in the tumor. Early generation isotransplants of a spontaneous fibrosarcoma, FSa-II tumors, were used. A radiation dose that yields 50% tumor control rate in 150 days after local irradiation, TCD50, was determined. Cyclophosphamide (CY) was the test agent. TCD50 values of the 4 mm tumor following gamma-ray alone given under hypoxic conditions or in air were 80.9 or 65.8 Gy, respectively. Thermochemotherapy reduced TCD50 values congruent to 20 Gy, suggesting that thermochemotherapy resistant cells are not identical to the radioresistant cells. Glucose administered 60 min before thermochemotherapy further reduced TCD50 values. Foot-reaction scored in the tumor-controlled animals was significantly less severe following combined thermochemo- and radiotherapy compared to that following radiotherapy alone. Acute foot reaction studies also supported this observation. These results indicated that thermochemotherapy could be an excellent adjuvant to radiotherapy. Further studies using a 6 mm tumor indicated that thermochemotherapy was less effective on the large tumor than on the small tumor. Indirect analysis showed no significant changes in the size of hypoxic cell fraction following thermochemotherapy.

The influence of pre-treatment temperature on the thermal sensitivity of a mouse tumour

The response of tumours to hyperthermia was tested by giving graded heat treatments and assessing local control at 90 days. Mice were divided into three groups which were pre-treated for 3 days in ambient temperatures of 4, 21 or 35 degrees C. This enabled the mean tumour resting temperature to be varied by up to 11 degrees C, before subsequent heat treatment. For the heat treatments, the tumours were clamped in order to eliminate blood flow, resulting in uniform temperature distributions and hence more uniform thermal sensitivity. TCD50 values were used to construct Arrhenius plots. For all three pre-treatment temperatures, these plots demonstrated a factor of 1.6 increase in heating time per degree Celsius reduction in heating temperature. However, tumours kept in a 4 degrees C environment before treatment were more thermally sensitive than those kept in 21 degrees C conditions, while those in a 35 degrees C environment were more resistant. Pretreatment at 4 degrees C was equivalent to an increase of either 0.5 degree C in heating temperature or 28 per cent in heating time, compared with pre-treatment at 21 degrees C. Pre-treatment at 35 degrees C was equivalent to a reduction of either 0.6 degree C in heating temperature or 25 per cent in heating time. These data indicate that the pre-treatment tumour temperature is an important parameter, but the effect of heat treatment is more closely related to absolute heating temperature rather than to the increase in temperature above the normal resting level.

Effect of hyperthermia on the radiation response of Chinese hamster small intestine

The Chinese hamster small intestine was surgically exteriorised from the ligament of Trietz to the ileocaecal junction and heated for 8 min at 44.3 degrees C (a non-lethal dose) at various intervals before or after whole-body 60Co irradiation. Hyperthermia exposure immediately after irradiation reduced the LD50/7 from the control of 1,230 cGy to 798 cGy (thermal enhancement ratio, TER, of 1.5). At an interval between irradiation and hyperthermia of 2 h the LD50/7 was 935 cGy, and it remained at that value for intervals of 2-24 h. The increase in the LD50/7 by 2 hours after irradiation probably represents the repair of radiation damage that can interact with hyperthermia, and after two hours the two modalities interact independently. When the small intestine was exposed to 44.3 degrees C hyperthermia immediately prior to irradiation, the LD50/7 was reduced to 658 cGy (TER = 1.8). As hyperthermia and radiation treatments were separated the LD50/7 returned to the control value by 24 h and was unchanged over 24-72 h. This indicates that by 24 h, recovery from hyperthermia damage that could interact with radiation damage was complete. For the sequence hyperthermia----radiation, 33% of the hyperthermia damage was repaired by 1 h; whereas for radiation----hyperthermia, 85% of the radiation damage was repaired by 1 h. The sequence-dependent interaction of hyperthermia and radiation damage in normal tissues is complex, but the kinetics of interaction for the sequence radiation----hyperthermia seem to be predictable for several normal tissues in different species.

Thermal distributions in a water bath heated mouse tumor

In the past several years numerous investigators have employed various mouse tumor systems and a variety of heating methods to examine the effects of hyperthermia in vivo. These studies have led, in some cases, to different results in tumor response in what appear to be similar experiments. Our results indicate that these discrepancies may in part be attributable to variations in intratumor temperature and depend strongly upon the method and conditions of heating employed. In all cases, we have employed the C3H mammary carcinoma tumor system with the tumor implanted in the right hind limb of the mouse. All tumors were 7-9 mm in diameter at the time of the experiments. Water bath heating was employed with the animals under one of four possible conditions: the presence or absence of anesthesia, and the use or lack of core cooling. Thermometry was performed with an array of multiple microthermocouples, each less than 150 micron in diameter, implanted in the tumor in a grid-like pattern. Significant variations (1.0 degrees C for no anesthesia, p less than .01; 1.3 degrees C for Thorazine/Ketamine, p less than .001) in intratumor temperature were found across the tumor in the unperturbed state. These variations were essentially eliminated under all hyperthermic conditions. Control of core (rectal) temperature (with or without anesthesia) reduced the intratumor temperatures even though the water bath temperature was held constant resulting in variations between water bath and tumor temperatures of from 0.1-0.8 degrees C.

Preoperative hyperthermo-chemo-radiotherapy effective for carcinoma of the esophagus

We prescribed hyperthermo-chemo-radiotherapy preoperatively for 13 patients with esophageal carcinoma. Viable cancer cells disappeared in four out of 13 patients, and all of these four patients survive without recurrence 3 to 34 postoperative months, at this writing. In another seven out of the 13, cancer cells were extensively damaged, despite the presence of a small number of viable cancer cells, and three out of these seven died with a recurrence. For two, the treatment was ineffective, and they died of liver metastasis and a local recurrence, respectively. These findings suggest that preoperative hyperthermia combined with chemotherapy and radiation is highly effective for treatment of carcinoma of the esophagus.

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.

Differential cytotoxicity of cis-platinum and blenoxane against human carcinoma KBE cells in multicellular spheroids of different ages: response at different temperatures

Human KBE epidermoid carcinoma cells were reproducibly grown in suspension as multicellular spheroids (MCS). Initial aggregation at 48 hours is followed by a rapid diameter increase until day 10. The size increase then continues with daily refeedings, under the growth conditions used, but at a slower rate. When cells are treated in MCS with either blenoxane (bleomycin) or cis-diamminedichloroplatinum (II) (cis-platinum), the survival of cells (by cloning efficiency (CE) essay) varied from that of surface attached (SA) cells. The survival was dependent on the age of the MCS as well as their size; the age response was significantly different for cis-platinum and blenoxane. Hyperthermic incubation of KBE cells in MCS at different ages for 1 hour (40-43 degrees C) resulted in cell killing similar to that observed after hyperthermic incubation of surface attached cells. In combined hyperthermia/chemotherapy experiments, simultaneous treatment with blenoxane resulted in little or no increase in MCS cell toxicity at 40 degrees C; at 42.5 degrees C, there was increased toxicity. The increase in toxicity was similar for MCS of different ages. Upon simultaneous cis-platinum treatment, an increase in toxicity was observed at 40 degrees C, but only in older MCS. At 42.5 degrees C, an increased toxicity (relative to treatment at 37 degrees C) was observed in MCS of all ages. These results are, in general, similar to those described for other in vitro and in vivo systems, but emphasize the differences in the survival response which can result for treatment of human cancer cells in MCS of different ages over even a small size range (up to 1 mm diameter). This is much smaller than clinically detectable tumors. This reproducible human cancer cell multicellular spheroid model has great potential for representing the variability likely to be present in micrometastases of different sizes, and in small regions of solid tumors, and therefore for assisting in preliminary evaluation of combined modality protocols.

Tumor control and therapeutic gain with different schedules of combined radiotherapy and local external hyperthermia in human cancer

Tumor control and therapeutic gain have been evaluated in a series of studies on patients with multiple lesions employing different protocols of combined radiotherapy (RT) and local external hyperthermia (HT). Tumor response has been evaluated during a follow-up ranging 6 to 18 months. Therapeutic enhancement factor (TEF) was defined as the ratio of thermal enhancement (TE) of tumors to TE of skin, where TE was clinically evaluated as the ratio of percent response (i.e., complete tumor clearance and moist desquamation, respectively) after combined modality to percent response after RT alone. Local tumor control was constantly better in lesions treated with any combined modalities in comparison with RT alone. The use of high RT dose per fraction appeared to increase tumor control only in the combined modalities groups, the immediate (so called "simultaneous") schedule (HT at 42.5 degrees C/45 min, applied immediately after each RT fraction, twice a week) being more effective than the delayed (so called "sequential") treatment (HT at 42.5 degrees C/45 min, delivered 4 h after each RT fraction, twice a week). The combination of high RT dose per fraction with high temperature HT (45 degrees C for 30 min) achieved the best tumor control. No increased radiation skin reaction was observed when a conventional fraction size of RT was used (3 daily fractions of 1.5-2 Gy, 4 h interval between fractions) in association with HT (42.5 degrees C/45 min, every other day, immediately after the second daily RT fraction). A remarkable enhancement of skin reaction was observed, however, when using high RT doses per fraction in association with 42.5 degrees C HT, especially with the immediate treatment schedule. No enhancement of skin reaction was obtained after high RT doses per fractions and 45 degrees C HT because an active skin cooling by means of circulating cold water was used in these cases. Consequently, a good TEF (1.58) was obtained when conventional RT doses per fraction were used in association with 42.5 degrees C HT. TEF values of 1.40 and 1.15 were observed when high RT doses per fraction were employed in association with the delayed and immediate 42.5 degrees C HT, respectively. HT at 45 degrees C can be safely employed only when tumors can be heated selectively or at least preferentially in comparison with normal tissue; in the lesions treated with such a schedule a TEF of 2.10 was obtained.

Basic principles in hyperthermic tumor therapy

Literature on hyperthermic tumor therapy in the past 10 years has grown exponentially. Since 1975 three international symposia on cancer therapy by hyperthermia have been held. Hyperthermia is of clinical interest in the temperature range of 40 degrees-43 degrees C. Higher temperatures of 44 degrees-46 degrees C are not clinically realizable. With local heat application a higher elevation of tissue temperature is possible. Whole-body hyperthermia in men is limited physiologically, as the rate of complications increases exponentially above 42 degrees C. The heat dose normally is defined by temperature degree and time of temperature elevation. Hyperthermia has several effects on tumor cells. It influences proliferation activity; within the mitotic cycle, preferentially the M-phase cells and S-phase cells are thermosensitive. It is possible to synchronize tumor proliferation by heat. Hyperthermia inactivates tumor cells in hypoxic condition as well. This was demonstrated in vitro with tumor cells under varying oxygenation and with spheroid experimental tumors. Experiments with solid tumors in animals had the same effect. Hyperthermia enhances the effect of radiation on tumors. In solid human tumors only 3%-5% of cells are in growth fraction; 95% of tumor cells are hypoxic or prenecrobiotic. Only well-oxygenated cells are sensitive to a sparsely ionizing radiation and can be killed. This selective radiosensitivity is the reason why other radiation qualities for radiotherapy, which are also effective on hypoxic cells, are examined. Neutrons and heavy ions are densely ionizing radiations, which inactivate hypoxic radioresistant cells. Hyperthermia in combination with sparsely ionizing radiations--e.g., X-rays or gamma rays--could be an alternative to neutrons or heavy ions. The main problem with heat application in clinical radiotherapy is the lack of heating methods which are able to heat the entire volume of a large solid tumor homogeneously. In small experimental animals there is a TER of about 1.5-2.0. The therapeutic gain of additional heat in radiotherapy is greatly dependent on localization of the tumor (skin, extremities) and on cooling of the skin. Hyperthermia enhances cytostatic drugs. Many investigations have been done on the interaction of heat and cytostatics; in vitro experiments evaluated three types. First, the activity of many drugs increases slightly with temperature; no special effects are observed above 42 degrees C. Examples of drugs of that pattern are the hypoxic sensitizer Ro-07-0582 and the alkylating agents thio-TEPA and CCNU. A second type of mechanism is seen with cytostatic drugs which exhibit greatly increased effectiveness at temperatures above 42 degrees C; adriamycin and bleomycin belong to this type.(ABSTRACT TRUNCATED AT 400 WORDS)

Histology as a method for determining thermal gradients in heated tumours

It is proposed that histological assessment of tumours may be a useful biological thermal dosimeter. Assessment of nodules may give information about thermal gradients, and biopsies of treated tumours may serve as a prognostic indicator in clinical hyperthermia. Cell death after hyperthermia occurs rapidly and surviving cells are readily recognizable as small foci within 24 h. This contrasts with the delayed cell death and the more random distribution of survivors amongst killed cells after ionizing radiation. By 24 h, sections of tumours can demonstrate islands of apparently viable cells in a sea of necrosis after 44.8 degrees C/1 h. This technique has been used to identify regions of poor heating in mouse tumours treated by water immersion. Cells surrounding blood vessels and cells adjacent to underlying normal tissue were seen to be protected from thermal damage.

Effect of hyperthermia and misonidazole on the radiosensitivity of a transplantable murine tumor: influence of factors modifying the fraction of hypoxic cells

Hypoxia has been demonstrated to play an important role in the effect of hyperthermia on tumors. We have studied the influence of different factors modifying the oxygenation status of a transplantable murine mammary adenocarcinoma (tumor volume and pentobarbital sodium anesthesia). The effect of hyperthermia alone on the tumor is not significantly influenced by the change in oxygenation status during the growth of the tumor. Also, the large increase of the acutely hypoxic cell fraction, as a result of anesthesia, does not change the effect of hyperthermia alone. In the combined irradiation-heat treatment there is a clear influence of the chronically hypoxic cell fraction on the response to hyperthermia: an increase in tumor size, resulting in a larger hypoxic cell fraction, leads to an increase in thermal enhancement ratio. However, the increased acutely hypoxic cell fraction, resulting from anesthesia, did not lead to an increase in thermal enhancement ratio; in fact the enhancement ratio apparently decreased. In spite of the fact that hyperthermia was applied immediately after irradiation no potentiation of radiation effects was found. The thermal enhancement of the radiation response was never larger than the enhancement as a result of misonidazole. All thermal enhancement could be explained by effects of heat on the chronically hypoxic cell fraction. Misonidazole had no effect on the response of tumors to heat alone, but greatly enhanced the effect of heat combined with irradiation. Anesthesia of the animals did not influence these effects of misonidazole.

Effect of hyperthermia on a neurogenic rat cell line (BT4A) in vivo

The effect of hyperthermia alone on the growth of the BT4A neurogenic tumour implanted into the feet of BD IX rats has been investigated. Following treatment by immersion of the tumour-bearing leg in a water bath at 42.0 to 45.0 degrees C a temporary retardation of tumour growth was observed but no cure. The lag phase before regrowth occurred was temperature and time dependent. A log-liner correlation was found between the surviving fraction previously found in vitro and the heat sensitivity of the cell line in vivo.

Microwave-induced hyperthermia and ionizing radiation. Preliminary clinical results

The combination of microwave-induced (2450 MHz) hyperthermia and ionizing radiation was used in 7 patients with superficial malignant tumours, which were considered refractory to other therapy. A newly developed heating system was used, allowing for a maintained temperature at the master probe of 42.5 degrees C +/- 0.5 degrees C during 45 min, but temperature measurements at multiple sites showed a marked variation. This preliminary series indicates that the combination of hyperthermia and ionizing radiation may be useful, the response rate (complete or partial) being 8 of 8 evaluable lesions. Even previously heavily irradiated sites responded. Technical improvements are highly needed to allow for controlled heating of any tissue volume.

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

The thermal enhancement of X-ray damage to mouse jejunum has been assessed when heating was achieved by immersion of an exteriorized loop of intestine in Krebs-Ringer solution. The results have been compared with those previously obtained following heating in situ. The primary effect of 1 hour of mild hyperthermia was to reduce the should of the crypt survival curve obtained following X-rays given alone. Thermal enhancement ratio (TER) values increased with increasing temperature, up to 42.3 degrees C, and were within the range reported for other normal tissues. However, when hyperthermia itself caused crypt loss and the contribution of hyperthermal killing to the overall tissue response was taken into account, there was little enhancement of radiation damage. There was no evidence of a large increase in TER at high temperatures, as is seen in some tumours and has been reported by Merino, Peters, Mason and Withers (1978) for intestine. It is possible that very high TER values which have previously been reported mainly reflect the heat-alone component of damage. Some of the implications of these results are discussed in relation to the combination of heat and radiation in therapy.

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.