Evidence for repair capacity in mouse tumors relative to skin

The clinical and histopathological effects of prednisone on acute radiation-induced dermatitis in dogs: a placebo-controlled, randomized, double-blind, prospective clinical trial

This study evaluated and compared the clinical and histopathological effects of prednisone on acute radiation-induced dermatitis (ARID) in dogs treated with 48 Gray of fractionated irradiation targeted to the skin surface. The study was designed as a double-blind, randomized, placebo-controlled prospective clinical trial. Twenty-two otherwise healthy companion dogs completed the clinical study. Three dogs were excluded from complete histopathological analysis because the owner declined one (one dog) or both (two dogs) biopsies. The study duration for each dog was 36 days from the start of radiation therapy (RT) to the first re-examination post RT. Dogs were treated with either oral prednisone at 0.5 mg kg(-1) or sugar pill, daily. All dogs received 48 Gray of fractionated, standardized RT, beginning 2 weeks after tumour excision. Acute Radiation Morbidity Scores, Cutaneous Toxicity Extent and Severity scores, digital images, and impression cytology were carried out on days 1, 8, 15, 22 and 36. Four-millimetre skin specimens from days 15 (RT-11) and 36 (2 weeks after the last RT dose) were scored by a pathologist and a dermatologist, blind to specimen identity. A one-way analysis of variance for longitudinal data was used to compare scores between groups. Spearman's rho correlation coefficient was used to measure strength of association between clinical and histopathology scores (HPS). There was no significant difference in CUTES, AMS or HPS scores between groups. There was a strong correlation between clinical and HPS scores. Prednisone did not decrease ARID severity clinically or histopathologically.

Biological rationale and clinical experience with hyperthermia

Hyperthermia (HT) as an adjunct to radiation therapy (RT) has been a focus of interest in cancer management in recent years there have been numerous randomized and nonrandomized studies conducted to assess the efficacy of HT combined with either RT or chemotherapy especially in the treatment of superficially seated malignant tumors. The major impact of HT is currently on locoregional control of tumor. Heat may be directly cytotoxic to tumor cells or inhibit repair of both sublethal and potentially lethal damage after radiation. These effects are augmented by the physiological conditions in tumor that lead to states of acidosis and hypoxia. Blood flow is often impaired in tumor relative to normal tissues, and HT may lead to a further decrease in blood flow and augment heat sensitivity. Three major areas of clinical investigation have borne the greatest fruit for HT as adjunctive therapy to RT. These include recurrent and primary breast lesions, melanoma, and head and neck neoplasms. Thermal enhancement ratio was increased in all cases and is approximately 1.4 for neck nodes, 1.5 for breast, and 2 for malignant melanoma. In general, the most important prognostic factors for complete response (CR) are RT dose, tumor size and minimal thermal parameters minimal thermal dose (t43min), mean minimal temperature (Tmin) or T90, i.e., temperature exceeded by 90% of thermal sensors]. The number of HT fractions administered per week appears to have no bearing on the overall response, which may be indicative of the effects of thermotolerance. The total number of HT fractions delivered also appears irrelevant provided adequate HT is delivered in one or two sessions. The major prognostic factors for the duration of local control were tumor histology, concurrent RT dose, tumor depth and Tmin. Although numerous single institution studies showed increased CR rates and improved local control, the efficacy of HT as an adjunct to RT should be assessed with well-designed multi-institutional randomized clinical trials. Such clinical trials are underway.

Recovery kinetics in mouse skin and CaNT tumours

Recovery kinetics and recovery capacity were studied in a fast proliferating normal tissue, skin, and in an anaplastic mouse mammary carcinoma, CaNT. Three fractions per day of X-rays, repeated over 5 days, were given at varying interfraction intervals from 0 to 8 h. The rate of recovery in tumours (t1/2 = 0.31 +/- 0.15 h for local control) was significantly faster than in skin (t1/2 = 0.96 +/- 0.10 h). By contrast, the fractionation sensitivity of CaNT tumours was less than that of skin (alpha/beta = 43.3 +/- 8.5 Gy vs. alpha/beta = 7.9 +/- 0.2 Gy). Tissues with recovery half-times similar to or longer than that determined for skin would be at risk if interfraction intervals less than 6 h are used in regimes which involve the use of two or more fractions per day. This would be especially true for tissues that show a greater sensitivity to dose fractionation, and hence more sparing of radiation damage with hyperfractionation.

The effect of cisplatin on the repair of radiation damage in RIF1 mouse tumours in vivo

The effect of the antitumour agent cisplatin on repair of X-ray-induced damage was studied in RIF1 mouse tumours treated in situ. The response of tumours, assessed by growth delay, to 4 fractions of X-rays given at 5-h intervals was compared with that after single doses. The displacement between the curves was taken as a measure of repair. A single dose of 6 mg.kg-1 cisplatin given 0.5 h before the first fraction resulted in no detectable inhibition of repair despite a significant growth delay caused by drug alone. A dose of 2 mg/kg cisplatin given 0.5 h before each of the X-ray fractions did, however, cause some repair inhibition; a result confirmed by tumour control experiments. The schedule dependence for repair inhibition was the same whether the irradiations were carried out on clamped (fully hypoxic) tumours or under ambient conditions. Significant enhancement of radiation damage was seen after correcting for the effects of drug alone, whether or not repair inhibition occurred. The effects of cisplatin on normal stroma within the tumour (vascular damage) was also investigated by monitoring the regrowth rates of recurrent tumours. In contrast to the effects on tumour cells, no enhancement of damage or inhibition of repair was seen for this assay in the combined treatment schedules.

Radiotherapy of the rhabdomyosarcoma R1H of the rat: hyperfractionation--126 fractions applied within 6 weeks

The effect of a hyperfractionated irradiation treatment on the response of the rhabdomyosarcoma R1H of the rat was studied. Tumors were irradiated under ambient conditions with 126 fractions of X rays, applied in 3 fractions per day with a time interval of 8 +/- 1 hr between fractions on 7 days per week during 6 weeks. The total dose ranged from 54 to 90 Gy, that is the dose per fraction ranged from 0.43 to 0.71 Gy. Tumor response was assessed by tumor control probability and tumor net growth delay. The tumor response to the hyperfractionated treatment was found to be slightly more effective compared to the results obtained in a previous study where treatments with 6, 18, 30, and 42 fractions were applied. Since normal tissues are considerably spared with increased numbers of fractions, clinical studies with hyperfractionation seem to be very promising.

Microwave hyperthermia radiosensitized iridium-192 for recurrent brain malignancy

Twenty-one patients whose solitary detectable biopsy proven recurrent brain malignancies produced Central Nervous System (CNS) symptoms warranting further intervention received 60-minute 43 degrees C (180 degree-minute) interstitial 2450 MHz microwave hyperthermia fractions. All received brain teletherapy prior to recurrence. The first 15 received no brachytherapy and served as a toxicity pilot. All 15 enjoyed neurologic improvement, 12 symptomatic improvement, and 12 objective response as mass reduction and/or tumor necrosis. The next 6 patients were selected with more favorable Karnofsky performance status, no known active malignancy elsewhere, and received afterloading Ir-192 interstitial implantation juxtaposed to radiosensitizing hyperthermia. Volume dose varied from 1000 to 2245 rad, and dose rate from 40 to 100 rad/hr. Dose selected varied as a function of pre-recurrence teletherapy dose, general condition, histologic type, and volume. Neurosurgical debulking, if technically indicated through no additional aperture or trauma, was permitted if consistent with preservation of neurological function. Six enjoyed neurologic improvement, symptom reduction, and objective tumor response; three remain alive, and one experienced transient improvement. Complications, histologic subtypes, autopsy findings, stereotactic approach, thermal monitoring methods and CT follow-up of objective response are presented along with computer dosimetry and isotherm chart. Our microtraumatic universal catheter technique for CT guided stereotactic biopsy, aspiration, decompression, thermal sensory loop, thermalization antennae, and brachytherapy without multiple trauma nor changing catheters is stressed. The rationale for combined modes peculiar to the CNS will be outlined.2+ Proposal for incorporating controlled-release ARA-C chemotherapy polymer micro-rods into the interstitial format will be offered. The preceeding is an FDA-approved controlled clinical trial.(ABSTRACT TRUNCATED AT 250 WORDS)

Radiotherapy of the rhabdomyosarcoma R1H of the rat: kinetics of cellular inactivation by fractionated irradiation

The kinetics of cellular inactivation by fractionated irradiation in the R1H rhabdomyosarcoma of the rat was studied in the dose range of 1.07 to 12.50 Gy per fraction. Regimens of 1, 3, 5, 7, and 10 fractions per week for several weeks were compared. The number of clonogenic tumor cells per tumor in the course of the different treatment schedules was determined using an in vitro colony assay. The results show that the proliferation of clonogenic tumor cells is decelerated in the course of a fractionated radiotherapy. The deceleration persists for several days after end of treatment, until accelerated repopulation is initiated. The fraction of tumor cells inactivated per week was only dependent on the total dose per week, that is the cellular response was the same whether the weekly dose was applied in 1,3,5,7, or 10 fractions. Thus, the fractionation regimens were considerably more effective than expected from calculations based on single-dose in situ survival curves.

Additivity versus repair inhibition in fractionated treatments combining drugs and X rays: a theoretical analysis

Drugs which inhibit the repair of radiation damage could potentially be useful for enhancing the effects of radiotherapy. In pre-clinical combined modality studies, however, it is often difficult to state with certainty whether or not a drug has inhibited radiation damage repair. This paper shows that several commonly used parameters for assessing repair can give the wrong answer regarding the presence of drug-induced repair inhibition. These parameters are; the difference in radiation dose between 1 and n fractions to give the same effect, the fractional recovered dose per fraction interval, FR, and the related parameter FREC. A further parameter used for treatment comparisons is the enhancement ratio for the drug (D.E.R.; ratio of radiation doses, with and without drug, to cause a given effect). An increasing D.E.R. with increasing number of radiation fractions has been taken as an indication that the drug inhibited repair. The present report demonstrates that this, too, can be misleading. From an analysis based on a linear-quadratic survival curve for X rays, it is suggested that deriving and comparing alpha/beta ratios (ratio of the linea to quadratic coefficients) gives the best indication of drug-induced changes in survival curve shape which may reflect underlying changes in repair capacity.

Tumor hypoxia: its impact on cancer therapy

The presence of radiation resistant cells in solid human tumors is believed to be a major reason why radiotherapy fails to eradicate some such neoplasms. The presence of unperfused regions containing hypoxic cells may also contribute to resistance to some chemotherapeutic agents. This paper reviews the evidence that radiation resistant hypoxic cells exist in solid tumors, the assumptions and results of the methods used to detect hypoxic cells, and the causes and nature of tumor hypoxia. Evidence that radiation resistant hypoxic cells exist in the vast majority of transplanted rodent tumors and xenografted human tumors is direct and convincing, but problems with the current methodology make quantitative statements about the magnitude of the hypoxic fractions problematic. Evidence that radiation resistant hypoxic cells exist in human tumors is considerably more indirect than the evidence for their existence in transplanted tumors, but it is convincing. However, evidence that hypoxic cells are a significant cause of local failure after optimal clinical radiotherapy or chemotherapy regimens is limited and less definitive. The nature and causes of tumor hypoxia are not definitively known. In particular, it is not certain whether hypoxia is a chronic or a transient state, whether hypoxic cells are proliferating or quiescent, or whether hypoxic cells have the same repair capacity as aerobic cells. A number of new methods for assessing hypoxia are reviewed. While there are still problems with all of the new techniques, some of them have the potential of allowing the assessment of hypoxia in individual human tumors.

Response of human tumour xenografts to fractionated X-irradiation

The response of two human tumour xenografts to single dose and fractionated X-rays has been tested using regrowth delay as the assay. The tumours were line transplanted cells from a moderately well-differentiated squamous carcinoma of the tonsillar fossa (XJ) and an undifferentiated carcinoma of the floor of the mouth (XR). Comparison of the dose response curves for single doses in air, clamped, or after misonidazole administration, led to estimates of the hypoxic fraction (approximately 15%) and the sensitizer enhancement ratio (less than or equal to 1.6). When 5 daily fractions were used, the effect of misonidazole (miso) was lost and reoxygenation appeared to be effective in both tumours. Comparison of single doses and 5 fractions in clamped tumours, and in those sensitized by miso, allowed the sparing effect of fractionation to be estimated. When analysed by the linear quadratic model the alpha/beta ratios were found to be in the range of 6.4-9.2 Gy and 6.8-16.0 Gy for the two tumours. These values are in good agreement with murine tumours (assayed in vivo or in vitro), with human tumour cells assayed in vitro, and with analyses of fractionated clinical data for skin cancer.

A review of alpha/beta ratios for experimental tumors: implications for clinical studies of altered fractionation

Clinical interest in the use of more and smaller dose fractions in radical radiotherapy has been stimulated by recent reviews of experimental results with normal tissues. It has been found that if the dose per fraction is reduced (i.e., in hyperfractionation) there is sparing of late responding normal tissues relative to those which respond early. This phenomenon can be understood in terms of the shapes of the underlying dose effect relationships, which can be described using the linear quadratic equation. The ratio (alpha/beta) of the linear (alpha) and quadratic (beta) terms is a useful measure of the curviness of such dose effect curves. Low alpha/beta values (1.5 to 5 Gy) have been observed for late responding normal tissues and indicate that radiation damage should be greatly spared by the use of dose fractions smaller than the 2 Gy used in conventional radiotherapy. By contrast the high alpha/beta values (6-14 Gy) observed for acutely responding normal tissues indicate that the response is relatively linear over the dose range of clinical interest. Hence less extra sparing effect is to be expected if lower doses per fraction are administered. If tumors respond in the same way as acutely responding normal tissues then hyperfractionation might confer a therapeutic gain relative to late responding normal tissues. We have reviewed published results for experimental tumors irradiated in situ and either assayed in situ or after excision. The alpha/beta ratios were usually at least as high as those for acutely responding normal tissues, and 36/48 tumors gave values greater than 8 Gy. Low values of less than 5 Gy were obtained for only 4/48 tumors. There are considerable technical problems in interpreting these experiments, but the results do suggest that hyperfractionation might confer therapeutic gain relative to late responding normal tissues on the basis of differences in repair capability. In clinical practice more efficient reoxygenation, cell cycle redistribution and decreased overall treatment time might also confer therapeutic gain.

The RBE for renal damage after irradiation with 3 MeV neutrons

Mouse kidneys were locally irradiated with single doses or up to 8 fractions of 240 kV X rays or 3 MeV neutrons. Damage was assessed from measurements of urine output, isotope clearance or haematocrit levels. All three assays gave steep dose-response curves by 4-5 months after irradiation. The repair capacity of the kidney was considerable after X-irradiation but was very small after irradiation with neutrons. Thus the RBE increased sharply with increasing fractionation. After large doses, an RBE of 2.3-2.5 was measured, rising to 4.5-5.1 after 8 fractions of 4 to 5 Gy X rays. Linear-quadratic analysis of these data has allowed RBE's to be calculated outside the measured dose range. The limiting RBE predicted at very low doses per fraction is 20 to 26, whereas at extremely high doses it would be as low as 1.2 to 1.4. This indicates that high RBE values may be seen in a slow turnover tissue after low doses per fraction (within the clinically relevant range) although this may not be evident after larger doses. Such high RBE's arise because of the shape of the underlying X-ray dose-response curve rather than the shape of the neutron curve.

Dose fractionation effects in low dose rate irradiation of jejunal crypt stem cells

Jejunal crypt survival after fractionated total body irradiation of C3H mice given at dose rates of 1.2 or 0.08 Gy/min was studied. The fractionation effect was more pronounced at the high dose rate than at the low dose rate. Analysis of the data according to the linear-quadratic survival curve model yielded an alpha/beta value at 1.2 Gy/min of 13.3 Gy and at 0.08 Gy/min of 96 Gy.

Multifraction irradiation of mouse bladders

The response of mouse bladders to multifraction irradiation was assessed from increases in urination frequency or the reduction in bladder capacity after irradiation. A range of electron doses were given as 1, 2, 5, 10 or 20 equal fractions in overall treatment times of 1-2 weeks. Dose-related increases in urination frequency were measured from 10 to 14 months after irradiation and a dose-related reduction in bladder capacity (at inflation pressures of 20 mm Hg) was apparent at the time of sacrifice. The extent of repair of sublethal and potentially lethal damage was estimated from a comparison of the isoeffective doses in fractionated regimes and single dose treatments. After small doses per fraction (2.5-6 Gy), the extent of repair in bladder was very similar to that in mouse skin. After larger doses per fraction (greater than 8 Gy) slightly more repair was seen in bladder than skin. Linear-quadratic analysis of the data suggests quite a high value for the ratio alpha/beta, in the region of 5 to 10 Gy. This is higher than the alpha/beta ratios which have been reported for most other slowly dividing normal tissues.

Endothelial proliferation in tumours and normal tissues: continuous labelling studies

The proliferation rate of vascular endothelium has been studied using repeated administrations of tritiated thymidine, given every 8 h for 1 week. Five experimental mouse tumours have been investigated and compared with placenta and with normal tissues. The large difference in labelling indices between tumour and normal endothelium that has previously been detected with single injections of ([3H]dT) is confirmed by these continuous labelling studies. The potential doubling time of the tumour endothelium is estimated to be between 2.4 and 13 days for the five tumours. Tpot for the placenta is at least as short. The turnover time of the normal tissue endothelium is estimated to be 20-2000 times longer (47-23,000 days) and does not seem to differ in slow turnover tissues e.g. lung and liver from that in tissues where the parenchymal cells are rapidly turning over e.g. jejunum or skin.

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.

The influence of the number of fractions and of overall treatment time on local control and late complication rate in squamous cell carcinoma of the larynx

Three hundred and ten patients with T3/T4, N0, M0 squamous cell carcinoma were irradiated with 200 kV X rays with total doses ranging from 4,900 to 6,200 rad, given in 21 to 35 fractions in 32-63 days. After a minimum follow-up period of 3 years, the local control rate was 50%; 21 severe late complications were observed among the patients. The dependence of local control rate and of late complication rate on the dose per fraction and on overall treatment time was analyzed by various statistical methods. Whereas the late complication rate depended significantly on dose per fraction, local tumor control depended strongly on overall treatment time.

Experimental results and clinical implications of the four R's in fractionated radiotherapy

Experimental and clinical data on the four R's in fractionated radiotherapy are reviewed. The clinical importance of redistribution has not been proven in the experiment yet. On reoxygenation no unequivocal data in human cancer exists and a lot of variability in rodent tumours. Repair and regeneration are the most important of the four R's in fractionated radiotherapy. The presented experimental and clinical evidence suggests a differential response between tumour and late responding normal tissues with regard to these two R's. Tumours appear to have, in general, a smaller capacity for repairing sublethal radiation damage but a higher capacity for repopulation than late responding normal tissues.