The effect of hyperthermia on the early and late appearing mouse foot reactions and on the radiation carcinogenesis: effect on the early and late appearing reactions

Negative Impact of Heat Exposure on Cosmesis after Conservative Treatment for Breast Cancer

Aim and background

To identify the factors influencing cosmesis after conservative treatment in breast cancer.

Methods

Retrospective analysis was done on 424 patients who underwent postoperative radiotherapy after conservative surgery for breast cancer from February 1992 to January 2002. Most of the patients underwent quadrantectomy. Whole breast irradiation up to 50.4 Gy was delivered in 28 fractions followed by a 10 Gy boost in 5 fractions to the tumor bed. Regional lymph node irradiation was administered if indicated. Breast cosmesis was scored in 4 tiers. Breast symmetry was analyzed by the relative distance from the sternal notch to the nipple, using photos taken prior to radiotherapy and 2 years after its completion. Median follow-up was 64 months.

Results

Breast cosmesis was excellent in 15%, good in 63%, fair in 19%, and poor in 3% of the patients. In multivariate analysis, tumors >2 cm ( P = 0.0109), lower quadrant location ( P = 0.0026), lymph node irradiation ( P = 0.0028), and heat exposure ( P = 0.0152) were related to poor cosmesis. The cosmesis score after radiotherapy compared to the pre-radiotherapy score was deteriorated in patients who had undergone lymph node irradiation ( P <0.0001) and heat exposure ( P = 0.0027). Breast symmetry was worse for patients who had tumors >2 cm ( P <0.0001), upper quadrant tumor location ( P <0.0001), chemotherapy in combination with radiotherapy ( P = 0.0136), lymph node irradiation ( P = 0.0006) and heat exposure ( P = 0.0355). Changes in symmetry by radiotherapy were greater for lymph node-irradiated patients ( P <0.0001).

Conclusions

With larger tumor size, lymph node irradiation, and chemotherapy in combination with radiotherapy, heat exposure was found to have a negative impact on cosmesis in patients undergoing conservative treatment for breast cancer. Patients should therefore be advised to avoid heat exposure after breast irradiation.

A biosafety evaluation of synchrotron radiation X-ray to skin and bone marrow: single dose irradiation study of rats and macaques

PURPOSE

Very limited experimental data is available regarding the safe dosages related to synchrotron radiation (SR) procedures. We used young rats and macaques to address bone marrow and skin tolerance to various doses of synchrotron radiation.

METHODS

Rats were subjected to 0, 0.5, 2.5, 5, 25 or 100 Gy local SR X-ray irradiation at left hind limb. Rat blood samples were analyzed at 2-90 days after irradiation. The SR X-ray irradiated skin and tibia were sectioned for morphological examination. For non-human primate study, three male macaques were subjected to 0.5 or 2.5 Gy SR X-ray on crus. Skin responses of macaques were observed.

RESULTS

All rats that received SR X-ray irradiation doses greater than 2.5 Gy experienced hair loss and bone-growth inhibition, which were accompanied by decreased number of follicles, thickened epidermal layer, and decreased density of bone marrow cells (p < 0.05). Macaque skin could tolerate 0.5 Gy SR X-ray but showed significant hair loss when the dose was raised above 2.5 Gy.

CONCLUSION

The safety threshold doses of SR X-ray for rat skin, bone marrow and macaque skin are between 0.5 and 2.5 Gy. Our study provided essential information regarding the biosafety of SR X-ray irradiation.

Animal models for medical countermeasures to radiation exposure

Since September 11, 2001, there has been the recognition of a plausible threat from acts of terrorism, including radiological or nuclear attacks. A network of Centers for Medical Countermeasures against Radiation (CMCRs) has been established across the U.S.; one of the missions of this network is to identify and develop mitigating agents that can be used to treat the civilian population after a radiological event. The development of such agents requires comparison of data from many sources and accumulation of information consistent with the "Animal Rule" from the Food and Drug Administration (FDA). Given the necessity for a consensus on appropriate animal model use across the network to allow for comparative studies to be performed across institutions, and to identify pivotal studies and facilitate FDA approval, in early 2008, investigators from each of the CMCRs organized and met for an Animal Models Workshop. Working groups deliberated and discussed the wide range of animal models available for assessing agent efficacy in a number of relevant tissues and organs, including the immune and hematopoietic systems, gastrointestinal tract, lung, kidney and skin. Discussions covered the most appropriate species and strains available as well as other factors that may affect differential findings between groups and institutions. This report provides the workshop findings.

Caffeine ameliorates radiation-induced skin reactions in mice but does not influence tumour radiation response

Intramuscular administration of caffeine at a dose of 80 mg kg(-1) body weight to the gastrocnemius muscles of Swiss mice 5 min prior to local irradiation (35 Gy) of the leg delayed the progression of radiation-induced skin reactions in such animals. While 90% epilation with reddening of the skin was noted in animals treated with radiation alone, animals pretreated with caffeine suffered only partial hair loss with slight reddening of the skin on the 16th and 20th days post-irradiation. Beyond the 28th day, damage scores in irradiated feet for both the groups were similar (score 3) and remained unchanged until the 32nd day and then decreased and disappeared completely in both treatment groups by the 40th day after irradiation. In addition, the effect of caffeine on the radiation response of a mouse fibrosarcoma was investigated. Results showed that intratumoral administration of caffeine at a dose of 80 mg kg(-1) body weight 5 min prior to local exposure of tumours to 10 Gy of 60Co gamma-rays did not influence the response of tumours to radiation. The present study thus showed that although caffeine ameliorated radiation-induced skin reactions in the mouse leg, it did not affect the tumour radiation response, indicating its potential application in cancer radiotherapy.

Are hypoxic cells critical for the outcome of fractionated radiotherapy in a slow-growing mouse tumor?

PURPOSE

To investigate the significance of hypoxic cells, reoxygenation and repopulation for the outcome of fractionated radiotherapy of a slow-growing subline of a murine fibrosarcoma and to compare the results with those previously obtained from the original fast-growing tumor.

MATERIALS AND METHODS

A slow-growing subline, 457-O, was obtained among the tumors that recurred after a single irradiation to the third generation isotransplants of a mouse fibrosarcoma, FSa-II. The single cell suspensions were transplanted into the mouse foot and when the tumors reached an average diameter of 4 mm, they were subjected to one to 20 equal daily y-ray doses given in air (A) or under hypoxic conditions (H). The TCD50 (50% tumor control radiation dose) was calculated according to the tumor control frequency within 180 days. The linear-quadratic plus time model was fitted to these data by logistic regression analysis.

RESULTS

The volume doubling time of the 457-O tumors was approximately 2.2 times slower than that of the original FSa-II tumors. The TCD50(H) (single dose) was 52.3 Gy and increased with an increasing number of fractions to a TCD50(H) (20 doses) of 90.8 Gy. This increase of 38.5 Gy was much smaller than that of 149 Gy for the original FSa-II. The TCD50(A) (single dose) and TCD50(A) (20 doses) were 41.3 and 50.6 Gy, respectively. This small difference of 9.3 Gy contrasted with a significant increase of 52.9 Gy for the FSa-II.

DISCUSSION

These results suggested no repopulation of 457-O tumor clonogens during the course of up to 20 daily doses, while the original FSa-II tumor cells repopulated substantially. Hypoxic clonogens in the slow-growing tumor reoxygenated but some fractions remained critical.

CONCLUSION

The present data together with those obtained from the fast-growing FSa-II suggested that hypoxic clonogens were critical for the outcome of fractionated radiotherapy. Repopulation was insignificant in this slow-growing tumor during five to 20 daily doses.

Results of alternating chemotherapy and hyperfractionated radiation therapy in childhood rhabdomyosarcoma

BACKGROUND

A regimen of multi-drug chemotherapy alternating with split course hyperfractionated radiation therapy (HFRT) was adopted for the treatment of patients with rhabdomyosarcoma (RMS). The purpose of this treatment regimen was to allow for the timely delivery of radiation and chemotherapy, reduce treatment-related toxicity, and improve compliance.

PROCEDURE

Forty-four patients with stages II-IV RMS were treated with HFRT and received 5,400 cGy. The treatment was administered in two courses (3,000 and 2,400 cGy) and separated by a 4-week interval. HFRT consisted of 150 cGy delivered twice a day, 5 days a week with an interfraction interval of 4-6 hours. A limited comparison was made between the HFRT patients and 42 historical patients with comparable clinical characteristics who were treated with similar chemotherapy and conventionally fractionated radiation therapy (CFRT) (median 4,800 cGy, range 4,000-5,680 cGy).

RESULTS

HFRT patients completed radiation therapy in 59.1 +/- 9.4 days (mean +/- SD) and CFRT patients completed treatment in 56.6 +/- 10.5 days compared to an expected 52 and 40 days, respectively. With a median follow-up of 55 months for the HFRT patients and 104 months for the CFRT patients, no differences in local control or survival were noted. Nine of 44 (21%) HFRT and 8/42 (19%) CFRT patients experienced local failure. The median time to local failure was 15 months for patients in the HFRT group and 11 months for patients in the CFRT group.

CONCLUSIONS

The results of the HFRT regimen were acceptable in terms of toxicity and compliance. No improvement in local control was obtained by alternating radiation and chemotherapy. The lack of difference between patients treated with HFRT and CFRT may be related to the lengthened treatment time of the split course regimen, the small difference in total dose, and tumor repopulation.

Delayed-accelerated hyperfractionated radiation therapy for advanced-stage or high-risk rhabdomyosarcoma

The treatment of six patients with advanced-stage or high-risk rhabdomyosarcoma (RMS) is described. These patients were treated with a delayed-accelerated hyperfractionated radiation therapy (DAHFRT) regimen which delivers 5200 cGy over 20 treatment days. Acceptable early toxicity was noted when radiation therapy was given after a full course of chemotherapy and major attempts at resection of the primary tumor. The DAHFRT regimen has inherent biological and time-intensity advantages compared to other fractionation schemes which may be exploited to improve local control. The DAHFRT regimen should be considered as an alternate fractionation scheme for RMS patients and a possible foundation from which dose-escalation of radiation therapy may be attempted using advanced treatment planning technology. Late effects of high-dose radiation therapy, although a major concern, should assume less priority given the high local failure rates of advanced-stage patients and the advent of conformed radiation therapy treatment planning and delivery which can be used to reduce treatment-related toxicity.

Increased tumour response of a murine fibrosarcoma to low temperature hyperthermia and low dose rate brachytherapy

The present animal tumour study was carried out to determine the effectiveness of low temperature hyperthermia combined with low dose rate radiation based on the cell culture studies of our laboratory and others that demonstrated a significant radiosensitization obtained by low temperature hyperthermia and low dose rate radiation. Well-oxygenated murine fibrosarcoma Meth-A tumours growing in Balb/c mice were treated with heat (41 degrees C tumour temperature) by immersion of the tumour-bearing leg in a waterbath concurrently with low dose rate radiation. Radiation was delivered using 192Ir interstitial implantation at absolute dose rates of 0.416-0.542 Gy/h. The effect of heat alone on tumour growth and normal tissue was minimal. Tumour growth delay following 30 Gy radiation was 4.9 days. Significant delay in tumour growth was observed with the addition of low temperature hyperthermia delivered concurrently. Enhancement in radiation response was seen with increasing duration of heat treatment; tumour growth delays were 9.5 days following 4 h heat (41 degrees C) treatment and 16 days following 6 h treatment. Three sessions of fractionated hyperthermia 4 h/day during the course of low dose-rate radiation significantly delayed tumour growth to 18.6 days. The results indicate that fractionated heat treatment in conjunction with low dose rate radiation has potential for improving tumour response without adversely affecting normal tissue reaction. This in vivo study represents an extension of the cell culture data and provides further radiobiological basis for the combined use of low temperature hyperthermia and low dose rate radiation.

Preliminary results of phase I/II study of high-dose-rate intraoperative radiation therapy for pediatric tumors

Ten children with locally advanced or recurrent tumors were treated on a Phase I/II study to assess the feasibility and toxicity of intraoperative radiotherapy (IORT) for primary and recurrent pediatric solid malignancies at high risk for local recurrence. Eligible patients include all primary and recurrent pediatric solid tumors that are amenable to resection and have residual microscopic or gross disease after surgery. In all cases, after a gross tumor resection was performed, a flexible, transparent, multichannel applicator was placed and secured within the tumor bed. Once the position of the applicator was optimized, the applicator catheters were attached to the cables of a high-dose-rate remote afterloader, and 1,200 cGy prescribed to 0.5-1.0 cm from the applicator was delivered to the tumor bed via the remote afterloader. One patient with a malignant teratoma developed a peri-rectal abscess 1 month after treatment; no other complications were noted. The 2-year actuarial local recurrence-free and distant metastases-free survival were 80% and 59%, respectively, with a median follow-up of 12 months (range: 3-18 months). The preliminary results suggest that high-dose-rate IORT is a safe and feasible modality for pediatric tumors at high risk for local recurrence. Longer follow-up will be needed to assess fully the toxicity and efficacy of this approach.

Successful treatment of orbital rhabdomyosarcoma in two infants using chemotherapy alone

Two infants, 2 months and 13 months of age, were found to have orbital embryonal rhabdomyosarcomas (ERMS). Because of the adversities associated with either surgical exenteration or curative doses of radiation therapy, they were treated with chemotherapy alone. They survive disease-free 5 and 9 years after diagnosis with excellent cosmesis and normal vision. This approach may be suitable for similarly small (< 2 cm in diameter) ERMS in other sites.

Effects of intraoperative irradiation and intraoperative hyperthermia on canine sciatic nerve: neurologic and electrophysiologic study

PURPOSE

Late radiation injury to peripheral nerve may be the limiting factor in the clinical application of intraoperative radiation therapy (IORT). The combination of IORT with intraoperative hyperthermia (IOHT) raises specific concerns regarding the effects on certain normal tissues such as peripheral nerve, which might be included in the treatment field. The objective of this study was to compare the effect of IORT alone to the effect of IORT combined with IOHT on peripheral nerve in normal beagle dogs.

METHODS AND MATERIALS

Young adult beagle dogs were randomized into five groups of three to five dogs each to receive IORT doses of 16, 20, 24, 28, or 32 Gy to 5 cm of surgically exposed right sciatic nerve using 6 MeV electrons and six groups of four to five dogs each received IORT doses of 0, 12,16, 20, 24, or 28 Gy simultaneously with 44 degrees C of IOHT for 60 min. IOHT was performed using a water circulating hyperthermia device with a multichannel thermometry system on the surgically exposed sciatic nerve. Neurologic and electrophysiologic examinations were done before and monthly after treatment for 24 months. Electrophysiologic studies included electromyographic (EMG) examinations of motor function, as well as motor nerve conduction velocities studies.

RESULTS

Two years after treatment, the effective dose for 50% complication (ED50) for limb paresis in dogs exposed to IORT only was 22 Gy. The ED50 for paresis in dogs exposed to IORT combined with IOHT was 15 Gy. The thermal enhancement ratio (TER) was 1.5. Electrophysiologic studies showed more prominent changes such as EMG abnormalities, decrease in conduction velocity and amplitude of the action potential, and complete conduction block in dogs that received the combination of IORT and IOHT. The latency to development of peripheral neuropathies was shorter for dogs exposed to the combined treatment.

CONCLUSION

The probability of developing peripheral neuropathies in a large animal model was higher for IORT combined with IOHT, than for IORT alone. The dose required to produce the same level of late radiation injury to the sciatic nerve was reduced by a factor of 1.5 (TER) if IORT was combined with 44 degrees C of IOHT for 60 min.

Neurological observations after local irradiation and hyperthermia of rat lumbosacral spinal cord

PURPOSE

Investigation of the effects of hyperthermia on the radiation response of rat lumbosacral spinal cord with respect to: (a) incidence of paralysis, (b) latency, (c) histopathology, and (d) tumor induction.

METHODS AND MATERIALS

Rat lumbosacral spinal cord with the cauda equina was single-dose irradiated with 15 to 32 Gy of x-rays. Hyperthermia for 30 min at a spinal cord temperature of 41.1, 42.3, and 42.6 +/- 0.4 degrees C was applied 5 to 10 min after irradiation by means of a 434 MHz microwave applicator. Animals were observed for 21 months while recording myelopathy and development of tumors.

RESULTS

The latent period for hind leg paralysis decreased with increasing radiation dose from 359 +/- 31 days (n = 9) after 20 Gy to 200 +/- 4 days (n = 5) after 32 Gy. Hyperthermia enhanced the radiation response of the lumbosacral spinal cord as evidenced by shortening of the latent period for paralysis and a decrease in the biological effective dose. After 20 Gy followed by 30 min 41.1 degrees C, latency was diminished to 214 +/- 16 days (n = 7, p < 0.001 vs. 20 Gy alone). The ED50 was 21.1 Gy, which was diminished to values between 16 and 17 Gy if radiation was followed by hyperthermia, giving a thermal enhancement ratio between 1.24 and 1.32. Histopathological examination of the spinal cord after combined treatment of x-rays and hyperthermia showed necrosis of nerve roots. Irradiation with 16, 20, 24, and 28 Gy (n = 77) alone led to tumor induction in 17 +/- 8% of the animals (pooled data). If followed by hyperthermia (n = 96), it was increased to 33 +/- 12% (p < 0.01). Most tumors induced by radiation and hyperthermia were sarcomas.

CONCLUSION

First, the radiation response of rat lumbosacral spinal cord was enhanced by heat. Second, latency for paralysis was shortened in the lower dose range. Third, no difference in pathology between x-rays alone or in combination with hyperthermia. Fourth, hyperthermia did increase radiation carcinogenesis.

Timing and sequence of hyperthermia in fractionated radiotherapy of a murine fibrosarcoma

PURPOSE

This study investigated the effect of timing and sequence of hyperthermia on fractionated radiotherapy, since it has been shown that the heat increases the size of hypoxic cell fraction which could affect the effect of subsequent radiation doses.

METHODS AND MATERIALS

Animal-tumors were early generation isotransplants of a spontaneous fibrosarcoma, FSa-II, in C3Hf/Sed mice. Tumor response was studied by tumor growth time and TCD50 (50% tumor control dose) assays. The tumor growth time is the time required for one-half of the treated tumors to reach 500 mm3 from the first treatment day. The TCD50 is a radiation dose to control one-half of the treated tumors for 120 days following treatments. One heat treatment at 43.5 degrees C for 45 min was given in a water bath in combination with fractionated doses independently (24 hr interval) or simultaneously (2 min interval). For the normal tissue study, the mouse foot was treated, and the acute foot reaction was scored daily and averaged. The late foot reaction was scored in animals used in the TCD50 assay that developed no recurrence for 120 days. The RD50(2.0) and RD50(5.0), or total radiation doses to induce an average score of 2.0 (complete epilation) and 5.0 (partial foot atrophy) in 50% of treated animals, were calculated.

RESULTS

Thermal radiosensitization was most prominent when heat was combined simultaneously with the first or last radiation dose in both the tumor growth time and TCD50 assays. However, the thermal enhancement was greatest when heat was given either with the first or last radiation dose in the TCD50 assay; whereas it was greatest when heat was administered with the last radiation dose in the tumor growth time assay. Both acute and late skin reactions were significantly potentiated by heat administered 24 hr before the first radiation dose.

CONCLUSION

A significant observation in this study was that, in both the tumor growth time and TCD50 assays, heat given independently or simultaneously did not result in any therapeutic gain compared to the radiation alone treatment.

Comparative study of thermoradiosensitization by misonidazole and metronidazole in vivo: antitumour effect and pharmacokinetics

Tumour control by local hyperthermia (43.5 degrees C, 30 min) and radiation (20 Gy) given in combination with misonidazole (MISO) or metronidazole (METRO) was studied using FSa-II murine fibrosarcoma. When MISO or METRO (5 mmol/kg) was given 30 min before heat and subsequently treated with radiation, tumour regression was observed for both agents. Radiation dose-response curves for MISO and METRO with heating at 43.5 degrees C for 30 min were identical. Mouse foot reaction was used to evaluate local toxicity following combined heat, a nitroimidazole and radiation treatment. MISO enhanced the magnitude of foot reaction and prolonged the recovery time compared with heat plus radiation controls. There were no observable differences of foot reaction between animals treated with heat plus radiation and those animals treated with heat, radiation and METRO. Pharmacokinetics of the nitroimidazoles heated at 43.5 degrees C for 30 min in FSa-II tumours were investigated as a possible mechanism of thermal sensitization. Local hyperthermia did not alter the pharmacokinetics of METRO. Tumour concentration and tumour/plasma ratio of MISO were slightly decreased during heating. Since the hypoxic metabolism of the nitroimidazoles did not increase significantly during the heat treatment, the thermal enhancement of MISO or METRO radiosensitization cannot be explained by the increase in hypoxic cytotoxicity of the nitroimidazoles at elevated temperature alone. The two nitroimidazoles also were not accumulated in the tumour after heating. Therefore, alternation of pharmacokinetics is not the major mechanism for the thermal enhancement of nitroimidazole radiosensitization. The METRO radiosensitization effect became identical to that of MISO at elevated temperatures is of particular importance in clinical radiosensitization. The very low local and systemic toxicity together with the high efficacy of METRO at elevated temperatures will make it an attractive candidate as a future clinical radiosensitizer.

Late reaction following twice-a-day irradiations in the murine foot: possible repopulation or consequential late effect

The effect of twice-a-day irradiation on the foot reaction was studied in C3Hf/Sed mice. A numerical scoring system was used to evaluate the foot reaction that became visible shortly after irradiation. Peak reaction occurred on the 21st to 23rd day and reappeared after approximately the 200th postirradiation day. These reactions are called early- and late-appearing reactions, respectively. Animals studied for early-appearing reactions were continuously scored for more than 600 days after irradiation. The late-appearing reaction increased continuously or remained constant, but never decreased during the course of the experiments. Animal feet were irradiated with a fraction size from 1.0 to 5.0 Gy twice-a-day daily with a treatment interval of 6 and 18 hours, and varying numbers of fractions were given. A top-up dose of 20 Gy was given as the last dose. The late-appearing foot reaction following a fraction size of 1.5 Gy or greater increased with increasing total dose. However, the increase in the late reaction score with increasing total dose was trivial following multiple doses with a fraction size of 1.0 Gy, suggesting a possible repopulation during prolonged irradiation or that the observed reaction was a consequential late effect. The Fe-plot based on doses which induced fibrosis in one-half of the irradiated animals, showed an alpha/beta ratio of 6.57 +/- 0.62 Gy, and the presence of a breaking point at approximately 1.5 Gy. The alpha/beta ratios calculated by Joiner's method and Thames direct analysis were identical. The slope of the Fe-plot below 1.5 Gy was significantly steeper than that above 1.5 Gy.

Lack of thermal inhibition of radiation damage repair in the late-appearing foot reaction

Our previous study on early- and late-appearing murine foot reactions following combined hyperthermia and irradiation suggested that hyperthermia may not inhibit repair of sublethal and/or potentially lethal radiation damage for the late-appearing reaction. A series of split dose experiments was performed by using C3Hf/Sed mouse foot reaction, which showed both early and late responses in the same tissue. Hyperthermia given in a 43.5 degrees C water bath for 45 min inhibited radiation damage repair in the early-appearing reaction, but was not able to modify repair in the late-appearing reaction. The failure of thermal inhibition of radiation damage repair in the late-appearing reaction was observed regardless of the sequence of heat and irradiation. Complete repair appeared to require approximately 9 hr. Although it is unknown whether radiation damage repair can be completely inhibited in all late-responding normal tissues, the reduction in thermal repair inhibition in some late-responding tissues may be an advantage of "heat prior to irradiation" treatment over radiation alone.

Significance of additive heat effect in the therapeutic gain factor in combined hyperthermia and radiotherapy: murine tumor response and foot reaction

The thermal enhancement ratio (TER) and therapeutic gain factor (TGF) were evaluated for combined hyperthermia and radiation treatments of a murine fibrosarcoma, FSa-II. The TER is the ratio of the radiation dose that induces a given reaction without hyperthermia to that with hyperthermia. The TGF is defined as the ratio of TER for tumor response to TER for normal tissue response. Tumors in the subcutaneous tissue of the right foot were irradiated with graded radiation doses when they reached an average diameter of 6 mm (110 mm3). Hyperthermia was given by immersing animal feet in a constant temperature water bath 10 min before or after irradiation. The tumor growth time to reach 500 mm3 was obtained for each tumor and the median tumor growth time was calculated for each treatment group. For the normal tissue study, the non-tumor bearing murine foot was treated, as was the tumor, and the foot reaction was scored after treatment, according to our numerical score system for radiation damage, until the 35th post-treatment day and averaged. Using the fraction of animals showing a given average foot reaction score in a treatment group, the RD50, or the radiation dose to induce the given foot reaction or greater, was calculated. A single heating at 45.5 degrees C for 10 min and a step-down heating (first heat at 45.5 degrees C for 10 min immediately followed by the second heat at 41.5 degrees C for 60 min) prolonged the tumor growth time, indicating that hyperthermia per se resulted in some cell killing. The prolongation was greater following step-down heating than following single heating. These heat treatments alone induced no noticeable heat damage on the foot, but decreased the threshold dose observed on the radiation dose response curves for the foot reaction. Accordingly, TER and TGF were evaluated with or without normalizing this thermal effect. TER's for both tumor and foot responses without normalization were greater than the TER's after normalization and decreased with increasing radiation dose (between 1.9 and 7.1 or greater for tumor and between 1.3 and 4.3 or greater for foot reaction), whereas the normalized TER's were relatively constant (between 1.6 and 1.7 for tumor and between 0.7 and 1.5 for foot reaction). TGF's without normalization were greater than those obtained after normalization. The former was large at small doses and decreased with increasing radiation dose (between 1.5 and 4.0 or greater), whereas the latter was within 0.8 and 1.3 and relatively independent of radiation dose.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Thermal enhancement of radiation-induced leg contracture

Early and late damage in the normal tissues of the legs of mice was compared following treatment with radiation alone or radiation followed immediately by hyperthermia. Hyperthermia was given by immersing the hind leg in a water bath at 43.0 degrees, 43.3 degrees, or 43.5 degrees C for 1 hr. Damage was assayed by measuring leg contracture at various intervals from 5 to 365 days after treatment. At 5 days after treatment, only hyperthermia-induced contracture was observed. At 10 and 20 days, contracture increased with radiation dose in heated legs, but little contracture had developed in mice treated with radiation alone. By 45 through 365 days, however, contracture correlated with radiation dose both in mice treated with radiation alone as well as in those treated with radiation and hyperthermia. The greatest differential in the slopes of the dose response curves, suggesting hyperthermic radiosensitization, was seen 20 days after treatment. Nevertheless, at 365 days, contracture was still significantly greater in the mice treated with radiation and hyperthermia (43.5 degrees bath) than in the irradiated controls. Thermal enhancement ratios (TERs) were calculated from LCD50 values (LCD50 = radiation dose that would give a stated level of leg contracture in 50% of the mice). For greater than or equal to 3 mm contracture, TERs were 4.1 to 7.9 at 30 days, depending on bath temperature, but only 1.1 to 1.5 at 365 days. For an isoeffect of greater than or equal to 7 mm contracture, TERs were 1.9 to 5.3 at 30 days, and 0.8 to 1.8 at 365 days. Thus, contracture was enhanced more at 20 to 30 days after treatment with radiation and hyperthermia than at 120 through 365 days. Radiation damage not only appeared earlier in mice treated with hyperthermia than in those treated with radiation alone, but after the highest temperature tested (43.5 degrees bath), contracture was greater from 5 through 365 days after treatment than in controls treated with radiation alone.

Incidence of tumours in the cervical region of the rat after treatment with radiation and hyperthermia

The incidence of tumours in the irradiated cervical region in female Wistar (WU) rats after retreatment of part of the volume with hyperthermia was examined retrospectively. The cervical spinal cord (cervical 5-thoracic 2) was irradiated with a single dose of 15, 18 or 20 Gy. Ninety days thereafter, the cervical region was heated by means of a microwave applicator at a maximum temperature of 43 degrees C for 50-90 min measured at the vertebral column. Over a period of 18 months after treatment, animals were regularly observed. Neurological complications and the development of neoplasms were noted. From the 354 animals included in the study, 82 animals developed a tumour. Hyperthermia alone was not carcinogenic, but enhanced the carcinogenesis induced by radiation. The percentage of animals that developed a tumour inside the volume treated with hyperthermia 90 days after irradiation was significantly higher relative to radiation alone (33 +/- 5 per cent versus 4 +/- 2 per cent, P less than 0.001). The duration of the latent period before appearance of these tumours was not affected (355 +/- 18 days versus 425 +/- 54 days). No significant differences in the percentage of animals that developed a tumour at another site were observed between different treatment groups. Histology revealed that 88 per cent (14/16) of the examined tumours found inside the treated volume after hyperthermia and irradiation were soft tissue rhabdomyosarcomas. Outside the treated volume, most tumours were tumours of the mammary gland.

Fraction size-dependent acute skin reaction of mice after multiple twice-a-day doses

To study the effect of multiple daily fractions on acute murine foot reaction, the left feet of C3Hf/Sed mice were irradiated by a Cs-137 irradiator at intervals of 6 and 18 hr, alternately. Fraction sizes ranged from 1 to 12 Gy, and various numbers of fractions were given. At the end of fractionation, a top-up dose of 20 Gy was administered. The overall treatment time ranged from 2 to 21 days. The average skin reaction from 10 to 35 days after completion of irradiations was determined. The skin reactions started from 8 to 27 days following the completion of irradiations. The skin reaction after fraction sizes of 3.5 and 5 Gy was dependent on the total dose. The skin reaction after fraction sizes of 1.5 and 2 Gy showed a biphasic response; at lower total doses, the skin reaction was proportional to the total dose, but at higher total dose, the skin reaction reached a plateau. The average skin reaction at the plateau with fraction sizes of 1, 1.5, and 2 Gy were 0.79 +/- 0.03, 1.12 +/- 0.13, and 1.37 +/- 0.06, respectively. The alpha/beta ratio for acute skin reaction following the twice a day scheme was 9.09 Gy (at dose/fraction greater than or equal to 3.5 Gy). The plateau may be attributed to the effect of accelerated proliferation and a balance between cell depletion and proliferation during twice-a-day irradiations. It is also suggested that twice-a-day irradiations induce more proliferation in skin than once a day treatments.

In vivo 31P-NMR spectroscopy of murine tumours before and after localized hyperthermia

In vivo 31P-NMR spectroscopy was used to monitor the energy metabolism, apparent intracellular pH (pHNMR), and phospholipid turnover in subcutaneous fibrosarcomas (FSall) and mammary carcinomas (MCaIV) treated with hyperthermia (HT). Treatment consisted of elevation of tumour temperature to 43.5 degrees C for 15, 30 or 60 min (FSall) and 30 min (MCaIV). Experiments were performed on conscious mice with biologically relevant tumour sizes. Using water bath immersion, this study focused on acute heat-induced metabolic changes (up to 7 h post-HT). 31P-NMR spectra of both murine tumours were characterized by relatively high pretreatment levels of PME, Pi and NTP, and lower levels of PDE, PCr and DPDE. Following hyperthermia, NTP and PCr levels, as well as pHNMR, decreased in both tumour lines. This drop was accompanied by a prompt and dramatic increase in Pi. After heating for 15 min, the limited spectral changes observed for the high-energy phosphates and the marginal decline in pHNMR were nullified within 7 h, whereas Pi remained significantly elevated. With the exception of PME/NTP and PME/PDE, all relevant metabolic ratios (PCr/Pi, NTP/Pi, PME/Pi) decreased after heating and did not resolve thereafter. Upon longer heat exposure times the high-energy phosphates, pHNMR, NTP/Pi, PCr/Pi, and PME/Pi all decreased in a dose-dependent manner and remained at the respective lower levels. The PME/PDE ratio was increased after 43.5 degrees C/15 min whereas at longer heating times this ratio did not change. At comparable heat doses MCaIV tumours seem to exhibit changes similar to FSall tumours.

The effect of preirradiated tumour bed on the response of a murine fibrosarcoma to elevated temperatures

The effect of pretransplantation irradiation of tumour beds (tumour bed effect or TBE) on the response of tumours to elevated temperatures and on the kinetics of thermo-tolerance was studied. Animal tumours were early generation isotransplants of a fibro-sarcoma, FSa-II in C3Hf/Sed mice. The tumour bed or murine foot was irradiated with 0.8 or 16 Gy in air, and tumour cell suspensions were transplanted 1-35 days thereafter. Hyperthermia of various durations was given in a 45.5 degrees C water bath when tumours reached an average diameter of 6 mm (110 mm3), and the tumour growth (TG) time to reach 500 mm3 was obtained. Dose-response curves between the TG time and the treatment time were less steep for tumours in preirradiated tumour beds than for tumours in non-irradiated tumour beds, indicating that the tumours in preirradiated tumour beds were more resistant to hyperthermia compared to the tumours in normal tumour beds. This resistance appeared to increase with increasing preirradiation dose. Thermotolerance was equally developed in tumours in normal and preirradiated tumour beds. The time required to develop the maximum thermotolerance was identical for both tumours. This indicated that the TBE has no effect on the kinetics of thermotolerance. The implication of these results in clinical trials may be that the tumour which recurred after radiotherapy may not be a good candidate for hyperthermia.

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.