Early and late damage in the mouse rectum after irradiation and cis-diamminedichloroplatinum(II)

Modulation of radiosensitivity in Chinese hamster lung fibroblasts by cisplatin

The effects of cisplatin exposure time, concentration, and irradiation sequence on the sensitivity of Chinese hamster lung fibroblasts (V79) to gamma-ray exposure were examined. Based on clonogenic cell survival, the cisplatin concentrations corresponding to 50% cell survival (EC(50)) for exposure times of 1 h to 7 days followed a 2-phase exponential decay and ranged from 28.26 +/- 3.32 to 1.53 +/- 0.24 micromol/L, respectively. When cells were treated at EC(50) for exposures of less than 4 h and irradiated immediately, cisplatin inhibited the effect of radiation. Exposures of 4-6 h did not affect radiosensitivity. For exposures of 8-12 h, radiosensitization was observed, which disappeared at 14 h and reappeared for much longer cisplatin treatments. At the lowest achievable EC(50) (1.53 micromol/L), radiosensitization was observed if irradiation was delayed for 1-8 h. This enhancement in radiosensitivity disappeared for irradiation delays of 10-12 h, but reappeared when irradiation was delayed for 14-18 h. These data demonstrate that the mode of interaction between cisplatin and gamma-irradiation depends on the concentration and exposure time of cisplatin, as well as on the timing of irradiation after cisplatin administration. Consideration of changes in cell cycle kinetics may contribute to the improvement of treatment outcomes in adjuvant chemoradiotherapy involving cisplatin.

Microarray analysis to identify molecular mechanisms of radiation-induced microvascular damage in normal tissues

PURPOSE

Radiation-induced vascular injury can be a serious problem for cancer survivors. In capillary vessels, this manifests as telangiectasia, causing cosmetic problems when occurring in the skin and more serious problems, e.g. excessive bleeding requiring surgery, when occurring in rectal or bladder mucosa. In addition, thrombotic, inflammatory, and fibrogenic events play an important role in the development of late radiation injury in many tissues. However, the sequence of these events and the relationship between various mechanistic pathways is unclear. The purpose of this project is to identify genes that are differentially expressed in tissues with manifest vascular damage, with the ultimate goal of intervening in this process to block the progressive development of tissue injury.

METHODS AND MATERIALS

Microarray experiments were performed using amplified RNA isolated from irradiated mouse kidney and rectum, and from sham-irradiated controls, at 10 and 20 weeks after treatment. Tissue samples were also taken for histologic evaluation of vascular damage at 10, 20, and 30 weeks after irradiation. Expression profiles for irradiated and sham-irradiated samples were compared, and differentially expressed genes were identified after normalization procedures, using information from straight color, color reverse, and self-self experiments. The extent of overlap in expression profiles for kidney and rectum during the phase of vascular damage was also examined.

RESULTS

The mouse kidney experiments showed upregulation of 31 genes at 10 weeks and 42 upregulated genes at 20 weeks. Only 20 genes showed significantly increased expression at both time points. Some of these genes were of particular interest in terms of their known involvement in vascular injury and signal transduction pathways. Irradiated mouse rectum had 278 upregulated genes at 10 weeks and 86 upregulated genes at 20 weeks. Only 19 of the genes upregulated during the period of identified telangiectasia (10-20 weeks) were common to both tissues. These included jagged 1 and Kruppel-like factor 5 (KLF5), which are reported to play a role in vascular development and remodeling.

CONCLUSIONS

Microarray analysis of RNA from irradiated normal tissues is an effective tool for identifying new genes of potential interest in the development of late tissue injury. Such experiments should be regarded as generating testable hypotheses for mechanisms of radiation-induced injury.

Late complications of pelvic irradiation in 16 dogs

When external beam radiation therapy is administered to the pelvis, normal tissues irradiated may include the colon, small intestine, urethra, bladder, bone, and spinal cord. The objectives of this retrospective study were to determine the incidence and severity of late radiation effects following pelvic irradiation in dogs and to identify factors that increase the risk of these effects. Medical records of all dogs treated with curative intent external beam radiation therapy to the pelvic region between 1993 and 1999 were reviewed. Patients with follow-up longer than 9 months or any patient that developed late complications earlier than 9 months were evaluated. Sixteen dogs met criteria for inclusion in this study. All dogs were treated with a 6-MV linear accelerator with bilaterally opposed beams. Diseases treated included transitional cell carcinoma of the bladder, transitional cell carcinoma of the prostate, and anal sac apocrine gland adenocarcinoma. Four dose/fractionation schemes were used: 49.5 Gy in 3.3 Gy fractions, 54 Gy in 3.0 Gy fractions, 54 Gy in 2.7 Gy fractions, and 18 Gy intraoperative radiation therapy followed by 43 Gy external beam radiation therapy in 2.9 Gy fractions. Implantable chemotherapy in the form of an OPLA-Pt sponge was used in six dogs as a radiation potentiator. Colitis was the major late effect following pelvic irradiation, occurring in nine dogs (56%). Colitis was characterized as mild in three dogs, moderate in one dog, and severe in five dogs. Three of the dogs with severe effects suffered gastrointestinal perforation. All dogs with severe late effects received 3 or 3.3 Gy per fraction, and 80% received radiation potentiators. In the seven dogs that received 2.7 Gy or 2.9 Gy per fraction, late effects were classified as none (n = 5), mild colitis (n = 1), and moderate colitis (n = 1). Radiation therapy can be administered to the pelvic region with a minimal risk of late effects to the colon by giving smaller doses per fraction and avoiding systemic radiation potentiators.

Treatment-time-dependence models of early and delayed radiation injury in rat small intestine

BACKGROUND

The present study modeled data from a large series of experiments originally designed to investigate the influence of time, dose, and fractionation on early and late pathologic endpoints in rat small intestine after localized irradiation. The objective was to obtain satisfactory descriptions of the regenerative response to injury together with the possible relationships between early and late endpoints.

METHODS

Two- and 26-week pathologic radiation injury data in groups of Sprague-Dawley rats irradiated with 27 different fractionation schedules were modeled using the incomplete repair (IR) version of the linear-quadratic model with or without various time correction models. The following time correction models were tested: (1) No time correction; (2) A simple exponential (SE) regenerative response beginning at an arbitrary time after starting treatment; and (3) A bi-exponential response with its commencement linked to accumulated cellular depletion and fraction size (the 'intelligent response model' [INTR]). Goodness of fit of the various models was assessed by correlating the predicted biological effective dose for each dose group with the observed radiation injury score.

RESULTS

(1) The incomplete repair model without time correction did not provide a satisfactory description of either the 2- or 26-week data. (2) The models using SE time correction performed better, providing modest descriptions of the data. (3) The INTR model provided reasonable descriptions of both the 2- and 26-week data, confirming a treatment time dependence of both early and late pathological endpoints. (4) The most satisfactory descriptions of the data by the INTR model were obtained when the regenerative response was assumed to cease 2 weeks after irradiation rather than at the end of irradiation. A fraction-size-dependent delay of the regenerative response was also suggested in the best fitting models. (5) Late endpoints were associated with low-fractionation sensitivity and treatment-time dependence even in animal groups that exhibited minimal early mucosal reactions.

CONCLUSION

Radiation injury scores in this rat small intestinal experimental model cannot be adequately described without time correction. 'Consequential' mechanisms contribute to the development of late effects, even in animals that do not develop severe early mucosal injuries. The initiation of the regenerative response is subject to a fraction-size-dependent mitotic delay and is linked to the level of accumulated cellular depletion. The response does not cease at the end of therapy but probably continues until maximal healing has taken place.

Histopathological and morphometric analyses of late rectal injury after irradiation

The aim of the present study was to assess and quantify changes in the structural components of the rectal wall after irradiation with varying single doses of x-rays. A total of 70 CDF1/Bom male mice were irradiated at a selective 1.5 cm of the distal rectum with varying single doses of 0-30 Gy. At 32 weeks postirradiation the mice were sacrificed and the rectum was removed. Sampling of the specimens was based on unbiased stereological principles using systematic random sampling. Vertical tissue sections were used to estimate mucosal surface area density and to measure the thickness and volume fraction of the different intestinal wall layers. The surface area density decreased with increasing dose (p<0.02) due to pronounced injury of the crypts and mucosal morphology. The thickness and the volume fraction of the submucosa were significantly increased in the 20, 25 and 30 Gy treatment groups (p<0.0001 and p<0.0001), whereas the thicknesses of the mucosa, the lamina muscularis propria and the serosa did not change after irradiation. It is concluded that irradiation causes histopathological changes in the rectal mucosa and submucosa, and changes in the thickness of the submucosal intestinal layer. These changes were found to be dose-dependent.

Murine strain differences in the volume effect and incidence of radiation-induced colorectal obstruction

PURPOSE

Interindividual variation in the level of normal tissue damage after radiotherapy has been clinically observed. Murine models have suggested that there may be a genetic component to the variation in susceptibility of different radiation-induced normal tissue complications. Currently, there are no experimental data available describing interstrain differences in the "volume effect" for irradiated normal tissues, such as the colorectum. The aims of this study are to determine if there are strain differences in: 1. the incidence of colorectal obstruction; and 2. the volume effect, after irradiation of the colorectum using two mouse strains that are known to vary in their susceptibility for developing pulmonary fibrosis.

METHODS AND MATERIALS

Various lengths (5.2 to 22.9 mm) of the colorectum of male C57B1/6 and C3Hf/Kam mice were irradiated with a single dose (30 Gy) of 137Cs gamma rays. Also, various doses (20 to 35 Gy) were given to a single length (22.9 mm) of colorectum. The incidence of obstruction was determined as a function of length and dose at 6 months after irradiation. The Threshold Probability model was fit to the length-response data.

RESULTS

C57B1/6 mice developed colorectal obstruction at significantly higher incidence than C3Hf/Kam mice at all lengths after a single dose of 30 Gy. In addition, the data showed a strain difference in the threshold length of colorectum that had to be irradiated before obstructions were observed.

CONCLUSION

Strain differences in the incidence of radiation-induced colorectal obstruction were observed, consistent with previous studies that showed a strain difference in radiation-induced pulmonary fibrosis. The presence of a threshold length of colorectum that was different for the two strains is consistent with the concept that there may be a critical threshold amount of colorectal tissue that can tolerate a high dose without complication, and that the dimensions of the threshold may vary among individuals.

The effects of local X-irradiation on the distensibility of the rectum in rats

Proctometry was performed on female Wistar rats following irradiation of the rectum with single doses of 15, 18 and 22 Gy of X-rays. The results indicated a progressive increase in distensibility until week 29 after irradiation which was attributed to degenerative changes in the intestinal wall. A major factor which determines colorectal pressure is the neuromuscular activity, however, neuromuscular transmission was not affected by irradiation.

Chronic radiation damage in the rat rectum: an analysis of the influences of fractionation, time and volume

PURPOSE

Analysis of four different sets of experiments performed by the G.S.F. group in Munich investigating the late tolerance of the rat rectum to external or intracavitary irradiation.

MATERIAL AND METHODS

The endpoint was late rectal stenosis in female Wistar rats. The raw data were fitted to the linear-quadratic model by means of a likelihood maximization method (Direct Analysis). The model was altered to allow for repopulation, incomplete repair, and varying irradiated lengths of the rectum.

RESULTS

Fractionation sensitivity was high or intermediate (alpha/beta ratio values [95% confidence limits] ranging from 2.67 [0.86, 4.80] to 6.65 [2.21, 11.73] Gy). Significant repopulation occurred when treatments were longer than 5 days (Dprolif equal to 0.61 [0.20, 1.47] and 1.08 [0.58, 1.90] Gy/day, in fractions of 4 Gy). Another interpretation is that radiosensitivity changed during treatment. Repair half-time estimates ranged between 1.84 [1.52, 2.34] and 5.02 [2.83, 21.7] h. Finally, the present analysis indicated that the smallest surviving compartment capable of tissue rescue was about 1/50 to 1/100 of a 1 cm high cylinder of the rectum wall.

CONCLUSIONS

The radiobiological features of late stenosis in the rats are consistent with combined injuries of early and late responding components of the rectal wall. This raises some concerns about the possible danger of hyperfractionated treatments, where the beneficial impact of fraction size reduction may be obviated for interfraction intervals that are too short. Also, accelerated irradiation may result in more late complications because of increased early reactions.

Weekly cisplatin plus external beam radiotherapy and high dose rate brachytherapy in patients with locally advanced carcinoma of the cervix

PURPOSE

Prospective, single arm, Phase I/II trial performed to assess the efficacy and toxicity of the concomitant use of weekly cisplatin and pelvic radiotherapy in patients with locally advanced carcinoma of the cervix.

METHODS AND MATERIALS

Between December 1988 and April 1991, 50 previously untreated patients with bulky, locally advanced, squamous cell carcinoma entered the study. All patients were evaluated by a gynecologist and a radiation oncologist and were submitted to standard pre-treatment staging procedures. The International Federation of Gynecology and Obstetrics stage distribution was as follows: IIA three patients, IIB seventeen, IIIA two, IIIB 25, and IVA three. Radiotherapy consisted of 46 Gy external beam irradiation plus three high dose rate intracavitary treatments given on a weekly basis to a total dose of 30 Gy to point A. Cisplatin 30 mg/m2 was also given weekly starting on day 1 of radiotherapy.

RESULTS

With a median follow-up time of 27 months, complete response was seen in 88% (44/50) of the patients. The actuarial survival rate at 44 months was 65%. Total pelvic failure rate was 26% (13/50). Of the 44 patients who achieved a complete remission, only seven have failed in the pelvis. Distant disease was observed in 24% of the cases. Treatments were well tolerated with no patient requiring an interruption in the radiotherapy. However, the incidence of late gastrointestinal toxicity was high, with 10 patients developing a rectal ulcer (four colostomies for severe bleeding), two patients a small bowel obstruction, and two patients a recto-vaginal fistula. Moreover, gastrointestinal complications appeared sooner than expected, at a median follow-up time of 11 months after completion of treatment.

CONCLUSION

The combination of weekly cisplatin and radiotherapy appears to be a very effective regimen for patients with locally advanced carcinoma of the cervix, but resulted in a relatively high frequency of late gastrointestinal complications.

Late changes in the normal mouse bladder after irradiation alone or in combination with cis-DDP or cyclophosphamide, assessed by stereological analysis

Stereological analysis has been performed to investigate the late changes in the normal mouse bladder one year after radiation alone (10-25 Gy) or radiation (10-15 Gy) combined with cyclophosphamide (CTX), 100 mg/kg, or cis-diamminedichloroplatinum (II) (cis-DDP), 6 mg/kg. A significant increase in total volume of urothelium was found in the group treated with CTX combined with radiation compared with the control. The total volume of connective tissue in the muscular layer in the groups which received X-rays only showed a significant increase compared to the control. There also seemed to be an increase in the amount of connective tissue in muscular tissue, although this was not statistically significant, in the groups treated with CTX and irradiation compared with CTX alone. This indicates the importance of radiation in the development of late damage. Results from bladders treated with cis-DDP alone or combined with radiation were statistically inconclusive due to the small number of animals in each group. The group treated with CTX and radiation (15 Gy) showed a significant decrease in the total volume of lamina propria, but no difference was found in the other treatment groups when comparing connective tissue, the muscular layer or the amount of vessels and capillaries with their corresponding control groups. Stereological analysis seems a feasible method to demonstrate late bladder tissue changes encountered after irradiation alone or combined with chemotherapy.

Early and late injuries in mouse rectum after fractionated X-ray and neutron irradiation

PURPOSE

to assess mouse rectum tolerance to fractionated X-ray and neutron irradiation.

MATERIALS AND METHODS

doses per fraction ranged between 0.25 and 35 Gy for X-rays, 0.05 and 12 Gy for neutrons. Neutron top-up doses were added when the fractionated irradiation was given in fractions less than 2 Gy of X-rays or 0.35 Gy of neutrons in order to bring the damage into the detectable range. The early endpoints were the nadir of weight loss occurring within the first 2-3 weeks following irradiation and lethality by 2 months. The late endpoints were the peak of weight reached at maturity of the mice, the proportion of short feces in the daily fecal output at 10 months and lethality by 12 months. The linear-quadratic (LQ) model was fitted to the data (direct "one-step" analysis) and the estimated parameters were used to calculate relative biological effectiveness (RBE) values.

RESULTS

alpha/beta ratio estimates were for X-rays: 19.9 Gy [95% confidence limits: 15.2, 27.0] for weight nadir. 13.4 Gy [9.3, 19.5] for early lethality, 6.4 Gy [3.6, 11.0] for peak weight, and 6.9 Gy [4.2, 10.8] for late lethality, for neutrons 19.9 Gy [9.5, 61.0] for peak weight. The fecal-deformity data were poorly fitted by the LQ model. The RBE was slightly higher for acute endpoints than for the late ones when X-ray fraction sizes were equal to or larger than 10 Gy. However, the change in RBE with decreasing X-ray dose per fraction was much steeper for the late endpoints, so that it became equal to or even higher than for acute reactions at doses per fraction of 5 Gy or less.

CONCLUSION

Our results were consistent with those obtained from previously published studies using the same experimental system but larger doses per fraction.

Radiation effects in the colon. An experimental study in the rat

In an experimental study, resembling a clinical trial of preoperative irradiation, 10 + 10 Gy was given to the pelvic and lower abdominal region of rats with a 4-day interval. The early effect on the colonic wall was evaluated by myeloperoxidase activity and hydroxyproline content of the bowel wall and correlated to histological findings. Groups of animals were followed up to eight months after irradiation for evaluation of later effects. General effects of irradiation were seen as low WBC during the first week and delayed body weight development up to two months after irradiation. Local effect in the colonic wall was noted as an increase in myeloperoxidase activity (indicating a leucocyte accumulation) in irradiated parts of colon during the first 11 days and again significantly elevated after two months in parts of colon, irradiated as well as protected. This correlated well with histological findings of inflammatory reaction, atypia and dysplasia during the first 10 days after irradiation but not at two months after irradiation. Hydroxyproline content was not affected. There were no major complications due to irradiation seen in the late course of the study period.

Early and late changes in the normal mouse bladder reservoir function due to irradiation and cis-DDP

Early and late changes in the reservoir function of the mouse bladder were investigated after radiation alone or a combination of radiation and cisplatinum (cis-DDP). Bladder function was investigated by repeated cystometries. Treatments consisted of either single fraction radiation (5-10-15-25-30 Gy) or 20 Gy in combination with cis-DDP (6 mg kg-1; i.p.) administered at various time intervals from 14 days before until 14 days after radiation. At two selected time intervals (15 min and 4 h before) radiation was given at different dose levels (5-10-15-20 Gy). Within 30 days after irradiation a dose-dependent early response was noticed both in the radiation alone group and the group where cis-DDP was administered 15 min before radiation. The dose-response curve showed a slight but non-significant shift to the left in the combined treatment group (dose effect factor (DEF) = 1.18). Investigation of the early change in bladder reservoir function in the animals treated with 20 Gy alone or a combination of 20 Gy plus cis-DDP at various intervals in relation to irradiation demonstrated a significant increase in response when cis-DDP was administered 24 h and 15 min before and 4 h, 72 h and 336 h after 20 Gy (P less than 0.05). The reversible nature of the early damage was demonstrated. Late response was irreversible and significantly increased in most groups were cis-DDP was administered from 168 h before until 72 h after compared to radiation alone. Comparing groups treated with radiation alone with groups where cis-DDP was administered 15 min and 4 h before radiation revealed DEF values up to 1.45 (P less than 0.05), reflecting the significantly larger response in combined treatment groups. Survival was significantly decreased in all combined treatment groups compared to groups treated with radiation only and likewise survival was decreased in the group treated by cis-DDP alone compared to control (no treatment at all).

Early and late effects of cisplatin and radiation at acute and low dose rates on the mouse skin and soft tissues of the leg

The influence of radiation dose rate and drug dose on the combined effects of cisplatin (Cis-diamminedichloroplatinum (II] and radiation on the skin and soft tissues was studied in the C3Hf/SED mice. Localized acute-dose-rate irradiation (ADRI) at 3.345 Gy/min and continuous low-dose-rate irradiation (CLDRI) of the hind leg at 0.028 Gy/min with and without the drug was delivered using a 137Cs laboratory irradiator. Cisplatin at 6 or 11 mg/kg was given by intraperitoneal bolus injection 1 hour before ADRI or by continuous infusion during CLDRI. Acute skin reaction was scored from days 13 to 30 and late skin contraction and leg contracture were measured at days 90, 180, 270, and 360 after treatment. A marked dose-rate effect was observed for these early and late normal tissue endpoints. At a dose of 60 Gy of CLDRI, the dose rate factor (DRF = isoeffect dose at CLDRI/isoeffect dose at ADRI) was 1.82 for acute skin reaction and 1.76 for late skin contraction or leg contracture at day 270. However, there was no significant enhancement of these early and late normal tissue effects by cisplatin at 6 or 11 mg/kg at either acute or low dose rates. Thus neither drug dose nor radiation dose rate had a significant impact on the combined effects of cisplatin and radiation on the mouse skin and soft tissues of the leg.

Determination of X-ray-induced damage to the murine colon using tissue compliance measurements

A proctometroscope has been developed to measure the mechanical functioning of the colon in a murine model. A balloon-tipped probe is inserted into the colorectal region of anaesthetized mice and inflated hydraulically, at a constant rate, by a motor-driven syringe. Balloon pressure and volume are monitored, processed and plotted on a X-Y/t recorder. The balloon is inserted within the irradiated area, such that the centre of the balloon is 1 cm proximal to the anus, and inflated up to either a maximum volume of 100 microliters or a maximum pressure of 100 cmH2O, depending on which occurs first. Compliance (delta V/delta P) of the colon was measured at various intervals following X-irradiation, a dose-dependent decrease being observed at 24 weeks. This decrease was progressive with time out to 72 weeks postirradiation. The compliance measured, in both control and irradiated groups, was not dependent on the inflation rate used to make the determination, and no iatrogenic effects have been detected after repeated probing during a long-term study. The use of different anaesthetic agents was also investigated, no significant difference between the compliance of mice anaesthetized with the different agents being detected. Use of this technique provides fully quantitative data on the function of the colon following radiation injury, and provides an alternative to other physiological assays. The technique is non-destructive, rapid, easy to use and non-invasive to the tissue, thus the onset and progression of damage can be followed in each mouse over long postirradiation periods.

The RBE of euoxic and hypoxic Ehrlich ascites tumour cells irradiated with negative pions in vitro and in vivo

Ehrlich ascites tumour cells (EAT-F5) were irradiated in vitro with the sparsely ionizing "plateau pions" and with the more densely ionizing "peak pions". From cell survival curves obtained under euoxic and hypoxic conditions, the RBE for the production of irreparable lethal and potentially lethal damage was derived. Cells of the same strain were used to produce solid tumours in the leg muscle of mice. Survival of these cells irradiated in vivo was compared with the corresponding in vitro data. It can be concluded that a large fraction of hypoxic cells is present in these tumours and that repair takes place in vivo at least as much as under the in vitro conditions. These solid tumours were irradiated with 5 dose fractions of fast protons as reference radiation, and the probability pT of tumour destruction was determined as a function of dose. Irradiation with a spot of "plateau pions" indicated the same pT as a function of dose, but side effects in the intestinal tract increased also with dose, leading to the death of the animals. The probability for avoiding these side effects in the animals, pS, was also determined. Using both values, pT and pS, the probability for local tumour control was estimated. Irradiation with "peak pions" resulted in an RBE of about 2.5 for tumour destruction corresponding to the RBE found in vitro for the production of irreparable lethal lesions in hypoxic cells. Side effects in the mouse gut showed a RBE of 2.0, corresponding to irreparable lethal lesions in euoxic in vitro cells.

Anti-tumor effect of cisplatin, carboplatin, mitoxantrone, and doxorubicin on peritoneal tumor growth after intraperitoneal and intravenous chemotherapy: a comparative study

Tumor growth was studied in a peritoneal tumor model in the rat after intravenous and intraperitoneal administration of doxorubicin (4 mg/kg), mitoxantrone (2.5 mg/kg) and cisplatin (4 mg/kg) and after intraperitoneal administration of carboplatin (20 mg/kg). All treatments delayed tumor growth and intraperitoneal treatment was more effective initially than intravenous treatment for all drugs tested. Regrowth occurred between 2 and 7 weeks after treatment and was less pronounced after intravenous treatment. Tumor sizes in cisplatin treated rats 7 weeks after treatment were comparable after intraperitoneal and intravenous treatments. Intraperitoneal carboplatin even with a dose 5 times higher than cisplatin resulted in a less tumor growth delay in all stages of the treatment, compared to cisplatin. All cytostatic drugs, except carboplatin, induced loss of body weight. Weight loss was similar for intraperitoneal and intravenous treatment with both cisplatin and mitoxantrone while for doxorubicin the weight loss was significantly higher after intravenous treatment than after intraperitoneal therapy. Considering the "therapeutic index", defined as the ratio of tumor growth delay to weight loss, cisplatin had the highest "therapeutic index", 1.5 (intraperitoneal) and 1.7 (intravenous) compared to 0.3 (intraperitoneal) and 0.6 (intravenous) for Mitoxantrone and 0.4 (intraperitoneal) and 0.5 (intravenous) for doxorubicin. This indicated that cisplatin was the most favorable drug to use in this peritoneal tumor model for both intraperitoneal and intravenous treatment. The tumor growth delay was initially more pronounced after intraperitoneal cisplatin compared with intravenous.

The effect of cis-diamminedichloroplatinum(II) on radiation damage in mouse rectum after fractionated irradiation

The influence of cis-diamminedichloroplatinum(II) (c-DDP) on radiation injury in the rectum of mice was investigated after single dose and fractionated irradiation. Mice were exposed to single doses, or 2, 4 or 8 fractions of X-rays given daily (or twice a day for the 8 fractions) with or without 8 mg/kg of c-DDP. The incidence of rectal stenosis and of anal discharge were scored and a direct analysis of the data for linear-quadratic dose-dependence of damage was performed with correction for censoring. For each endpoint, c-DDP did not significantly change the dose-response curves after fractionated irradiation. Subtile modifications in the coefficients of the linear-quadratic relationship were observed. The drug appeared to increase the alpha term by a factor of 2.3 and the beta term by a factor of 1.5, but the differences did not reach statistical significance. For the rectal stenosis endpoint, the alpha/beta was 4.4 Gy after irradiation alone and 6.9 Gy after combination treatment. Again the differences were not significant. These data suggest that c-DDP did not reduce the repair capacity in the mouse rectum during fractionated irradiation. Combined modality therapy with c-DDP and radiation would therefore not be expected to cause an increase in late damage in the large bowel.

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.

Adhesion formation in experimental chronic radiation enteropathy

We have studied the late changes associated with radiation enteropathy in mice over a period of 224 days following single or split doses of gamma radiation delivered to the total abdomen (TAI). We focused on the importance of adhesion formation as a cause of strictures and gut-associated deaths following TAI. Gut-associated peritoneal adhesions were found in mice 2-7 months after receiving 13.5-17.5 Gy TAI and appeared to constitute the most consistent serious late effect of irradiation. There was a good correlation between adhesion formation and death for both the single and split-doses of radiation. Adhesions primarily involved the large gut, normally near the cecum. They appeared to result from serosal breakdown and were the major cause of partial gut obstruction. Submucosal fibrosis was present but seemed to be a comparatively minor cause of strictures. Local lymphoid hyperreactivity was also seen following TAI and may have contributed to the late sequelae. The complexity of the pathogenesis of chronic radiation enteropathy was indicated by finding three successive waves of non-scheduled deaths following TAI. The first wave (28-70 days) was not related to adhesion formation and may have been due to localized failure of mucosa to regenerate after irradiation with consequent ulceration. The second wave (98-140 days) occurred over the period when adhesion formation and fibrosis were most marked. In the third wave (168-224 days), the additional complication of fluid exudation was seen. Further experimentation is obviously needed to better define the complex pathogenesis of radiation enteropathy with dose and time after radiation but our data strongly support a multifactorial causation with an important role for adhesion formation in the disease complex.

Direct estimation of latent time for radiation injury in late-responding normal tissues: gut, lung, and spinal cord

Mixture models are proposed for simultaneous analysis of the latency and fractionation characteristics of radiation injury in late-responding normal tissues. The method is an extension of the direct analysis for quantal response data. Conceptually, the application of the mixture model is based on the biological observation that over a wide range of doses a proportion of the irradiated subjects will never express damage. Mixture models allow the time of occurrence to be utilized in the analysis. Furthermore, this type of model takes time-censored observations into account in a natural way and provides an adequate framework for modelling and analysis of effect-dependent latency. Mixture models with complete and incomplete repair are applied to dose-incidence data for four late endpoints in rodents: death from radiation-induced pneumonitis, leg paralysis after spinal-cord irradiation, and radiation-induced rectal stenosis and anal discharge. Radiation-induced pneumonitis had an effect-dependent latency. The modelling of this phenomenon correlates well with the results of histologic studies. Interestingly, the ratio of hazard rates was not constant for this endpoint. The dominating feature in the latency of radiation injury to the spinal cord was a strong dependency on dose per fraction. After correction for this effect a tendency towards a longer latent time for lower effect levels was observed. For the rectal complications, there was no difference between latency with radiation only vs. radiation combined with cis-platin.

Radiation tolerance of the rat rectum to fractionated X-rays and pi-mesons

A 2.5 cm segment of the rectum of female F344 rats was irradiated with up to 10 fractions of X-rays or pions. Transient signs of acute proctitis were followed by chronic rectal injury starting at about 2 months. Recto-vaginal fistulas were frequently observed in animals with severe chronic injury. Two patterns of chronic injury were observed, an early type consisting of deep ulcers and fistulas, and a late type characterized by vascular injury, fibrosis and mucosal cysts. In a 4-fraction X-ray experiment, the influence of a low-residue diet was compared with a regular diet, showing no significant differences in pathology or survival. Isoeffective doses were determined for the occurrence of severe rectal injury at 250 days. Fitting the data to an LQ-model yielded an alpha/beta ratio of 13 Gy for pions, and 6.5 Gy for X-rays. Increasing the overall treatment time from 9 days to one month gave a significant rise in isoeffective doses for chronic injury. This suggests that the more delayed types of injury did not develop independently from the acute mucosal changes. The RBE of pions for rectal injury at 250 days was 1.2 for single doses, increasing to about 1.4-1.5 at a dose per fraction of 4 Gy. These values are similar to those obtained in other acute and late responding tissues.

The search for therapeutic gain in the combination of radiotherapy and chemotherapy

The literature on combined treatment with radiation and cytotoxic drugs in experimental tumours and normal tissues of laboratory animals is reviewed in the context of the four previously proposed mechanisms whereby a therapeutic advantage might be gained. There is evidence for strong time-dependent processes occurring in some normal tissues. In tumours, the evidence for this is much weaker and there is considerable disparity among experimental tumours in optimum timing. This review leads to the conclusion that the clinical use of drug-radiation combinations should not be based on an anticipated beneficial interaction; gain will most probably come from the best radiotherapy and the best chemotherapy given as far as possible independently. Deleterious interactions can be reduced by allowing a gap of some weeks between chemotherapy and radiotherapy and by avoiding drugs that are known to enhance radiation damage to the normal tissues that are irradiated.

Concurrent daily cisplatin and radiotherapy in locally advanced squamous carcinoma of the head-and-neck and bronchus

In order to exploit the cytotoxic and radiosensitising actions of cis-platinum, we have treated 35 patients with locally advanced squamous cell carcinoma of the bronchus or head-and-neck. Each patient underwent radical irradiation (60 Gy/30 fractions over 6 weeks) with daily low-dose intravenous cisplatin (10 mg absolute dose per day) administered within 30 min of each daily radiation fraction. Total dose of cisplatin was 300 mg over 6 weeks. Although treatment was complicated by nausea in almost all patients and transient renal dysfunction in the majority, 27 patients completed treatment and renal function returned to normal or near normal in almost all cases. There was no obvious enhancement of pulmonary or skin toxicity, beyond what would have been expected from treatment with radical radiotherapy alone. There were two treatment-related deaths from renal failure. The response rate was high: all patients achieved at least a partial response, and in head-and-neck sites, there were nine complete responders and seven partial responders. Of the initial 35 patients, of whom all but two had advanced inoperable disease, 11 have died and 21 remain in continuous remission, 8-120 weeks from the start of treatment (median 55 weeks).