Sheri D. Henderson

Radiation therapy of 9L rat brain tumors

Abstract The effects of radiation therapy on normal rats and on rats burdened with 9L brain tumors have been studied. The heads of normal rats were X-irradiated with single exposures ranging from 1000 R to 2700 R. Followiag acute exposures greater than 2100 R, all animals died in 8 to 12 days. Approximately 30% of the animals survived beyond 12 days over the range of 1950 to 1950 R; following exposures less than 1850 R, all animals survived the acute radiation effects, and median survival times (MST) increased with decreasing exposure. Three fractionated radiation schedules were also studied: 2100 R or 3000 R in 10 equal fractions, and 3000 R in 6 equal fractions, each schedule being administered over a 2 week period. The first schedule produced a MST of greater than 1 1 2 years; the other schedules produced MSTs that were lower (192 and 145 days, respectively). It was determined that by applying a factor of 1.9, similar survival responses of normal rats were obtained with single as with fractionated radiation exposures. Animals burdened with 9L gliosarcoma brain tumors normally died of the disease process within 18–28 days after tumor inoculation. Both single and fractionated radiation therapy resulted in a prolongation of survival of tumor-burdened rats. This prolongation was found to be linearly dependent upon the dose; but only minimally dependent upon the time after inoculation (7–12 days) at which therapy was initiated, or upon the fractionation schedule that was used. As with normal animals, similar responses were obtained with single as with fractionated exposures when a factor (1.9) was applied. All imam-hearing animals died prior to the time that death was observed in normal, irradiated rats. Thus, the 9L gliosarcoma rat brain tumor model can be used for the pre-clinical experimental investigation of new therapeutic schedules involving radiation therapy and adjuvant therapies.

Bleomycin and brain tumors

A logical inference from the recent reports indicating that malignant brain tumors are composed of a heterogeneous cell population is that combination chemotherapy will be required for effective brain tumor control. For several years we have been investigating the use of Bleomycin as an agent to be used in conjunction with radiation therapy and a nitrosourea compound. Since systemically administered Bleomycin does not cross the blood-brain-barrier and has significant toxicity when used parenterally in high doses, we have studied the use of smaller doses of Bleomycin injected directly into the brain tumor cavity. Such an intracerebral dose was more effective in prolonging survival of rats burdened with experimental 9L gliosarcomas than an intravenous dose that is 25 times as great. The combination of intracerebrally administered Bleomycin and radiation therapy was more effective than either modality alone. Furthermore, the combination of Bleomycin delivered intracerebrally and BCNU given systemically was more effective than eitheragent used alone.Finally, in a Phase I clinical trial of Bleomycin given via an Ommaya reservoir to eight patients with recurrent malignant brain tumors, we have demonstrated that individual doses of up to 7.5 units and cumulative doses of up to 255 units can be administered without significant toxicity.

Dosimetry of CT-guided volumetric IR-192 brain implant

Over the past 2 years, an afterloading technique has been developed and refined to implant radioactive Ir-192 sources into brain tumors. The implantation procedure integrates a stereotaxic system with computerized tomography (CT), which provides tumor position, volume, and guides the placement of catheters. A radiolucent ring-frame immobilizes the head as holes are made at 1 cm intervals with the aid of a template. Catheters containing dummy sources 1 cm apart are then inserted to the desired depth, and their position verified in three dimensions to insure complete coverage of visible tumor volume as defined by contrast enhancement. Once catheters are secured, the anesthetized patient is moved to the intensive care unit where the dummy sources are replaced by ribbons of Ir-192 seeds (specific activity 0.6-1.0 mg Ra eq). CT scans with the dummy sources in place are used to designate spatial coordinates of the active sources. A computer program converts position data and source strength into isodose contours in any plane. The implant duration (70-100 hours) for the desired dose to the tumor periphery (60-120 Gy) is then calculated. Dose rate contours are superimposed on preimplant CT scans. Maximum and minimum doses are determined in each of the various planes. Verification dosimetry has been carried out with thermoluminescent dosimeters placed in a catheter located in a plane along the tumor periphery. In vivo isodose values compared to idealized plans agree within +/-5%-10%.

Response of the 9L rat brain tumor to combination treatment with radiation and bleomycin

Abstract The therapeutic efficacy of combined modality treatment with radiation therapy and bleomycin was investigated in rats burdened with the intracerebral 9L gliosarcoma. Both radiation (single or fractionated exposures) and bleomycin (injected intracerebrally directly into the tumor region) are effective in prolonging survival when used as single agents. Bleomcyin (1.0 mg/kg/week) combined with low-dose radiation therapy (15.3 Gy in 6 fractions in 2 weeks) prolonged survival over that of radiation alone, but not to the extent of high-dose radiation therapy (30.6 Gy in the same schedule). Bleomycin was effective whether given simultaneously or following fractionated radiation therapy-the important factor being delivery of radiation therapy early in the disease process. The greatest enhancement in survival caused by combination therapy compared to that by single agent therapy was observed when single exposure radiation therapy (20 Gy) followed single bleomycin administration by 4 hr. These results suggest the possibility of using bleomycin as an adjunct to radiation therapy for the treatment of patients with malignant brain tumors.

Comparison of cancer chemotherapeutic agents in asynchronous and synchronous 9L cells

The cytotoxic activity of various chemotherapy agents was investigated in asynchronous populations of cultured 9L rat brain tumor cells, and as a function of their position in the cell cycle. Representative drugs from the classes of DNA-active agents, alkylating agents, spindle poisons, and antimetabolites were tested. The ability to induce cell lethality in asynchronous populations as a function of drug concentration varied for 1 hr pulse exposures. In order of decreasing cytotoxic activity, DHAQ was the most effective, followed by VCR, VDS, VBL, ADR, BCNU, cis-DDP, BLM, DBD, RZ, and HU. The effect of chemotherapy agents on synchronous 9L cells obtained by mitotic selection also varied with respect to the individual agent and was cell cycle-dependent. Survival age-responses ranged from being minimal to demonstrating significant fluctuations as a function of cell cycle position. For all agents except ADR and HU, the sensitivity of G1 phase was greater than S phase. RZ exhibited essentially a flat age-response. Comparison of the cell cycle age-responses of chemotherapeutic agents to those exhibited by the cytotoxic modalities of radiation and hyperthermia demonstrate several unique differences.

Simple plethysmograph for measuring respiration rates in rats with lung damage

In order to measure respiration rates in rats irradiated to the whole thorax, a plethysmograph involving a microphone with extended low‐frequency response and an airtight, whole‐body chamber has been constructed. The microphone response to the respiration pressure waves created by the rats placed in the chamber is markedly greater in amplitude than the response to laboratory sounds and animal noises; thereby filtering complexities are avoided. The output from the microphone went to a frequency counter for measurement of the number of pressure waves per unit time. Control, unirradiated rats, between the ages of 3 and 18 months, demonstrated a respiration rate in the range of 130–160 breaths per minute. Rats that received thoracic radiation doses greater than 12 Gy displayed increased respiration rates and occasional abnormal respiration patterns. These results demonstrate that this whole‐body plethysmograph incorporating a sensitive microphone and simple electronics can be used for the measurement of respi...

Development of normal tissue damage in the rat subsequent to thoracic irradiation and prior treatment with cancer chemotherapeutic agents.

THE EFFECT OF COMBINED MODALITIES (radiotherapy-chemotherapy) on the development of long-term normal tissue damage was investigated in rats. Animals received single I.P. injections of Hanks balanced saline solution, adriamycin (ADR, 1.0 mg/kg), bleomycin (BLM, 10 units/kg), or dihydroxyanthraquinone (DHAQ, 3.0 mg/kg); and/or irradiation of the chest with 25 MV x-rays (12 Gy) at 0, 43, 93, or 199 days after drug treatment. Only animals treated with DHAQ displayed appreciable toxicity, with more animals dying at less than 200 days when radiation was added at 0 or 43 days. Although animals treated with BLM or radiation exhibited evidence of lung damage (histologi-cally by 199 days and radiographically by 300 days), their survival was not compromised. The simultaneous administration of x-ray and BLM produced enhanced effects as compared to either agent alone. These results demonstrate an enhancement of normal tissue damage by combined treatment with radiation and chemotherapeutic agents, not only for acute toxicity but also for long-term effects. This damage was ultimately expressed as alteration of lung structure (histologically and radiographically) in the case of BLM, and as animal lethality in the case of DHAQ. In addition, there was a reduction in the degree of enhancement observed as a function of the separation in time between treatment with chemotherapeutic agents and subsequent irradiation. These factors should be considered when combined modality therapy is used for treatment of cancer in the thoracic region.

Effect of dihydroxyanthraquinone on the response of a rat solid tumor to radiation therapy.

DIHYDROXYANTHRAQUINONE (DHAQ, NSC 279836, a new cancer chemotherapeutic agent presently in clinical trials) was tested, alone and in combination with radiation, for therapeutic effectiveness in a rat solid tumor model. The Walker 256 fibrosarcoma was implanted subcutaneously in the leg via trochar so as to yield palpable tumors within 7–11 days. When tumor diameters reached 1 cm, the animals were treated as follows: as controls; with DHAQ (3.0 mg/kg, i.p.); with 300 KVP x-rays (15 Gy to the tumor-burdened leg); or with a combination of DHAQ and radiation. Tumor diameters were measured three times a week to monitor the response to therapy. DHAQ alone had no effect on tumor growth rate. Radiation alone produced a delay in tumor growth. The combination of DHAQ and radiation resulted in a consistently better therapeutic response than did radiation only, but at only a marginal level of statistical significance (0.05 < p < 0.10). However, there were 3/10 long-term survivors (>80 days post treatment) without evidence of tumor in the combination therapy group; whereas all animals in the radiation group died or were sacrificed because of progressive tumor growth by day 71. These results suggest that even though DHAQ is only minimally effective against this rat solid tumor when used alone, there may still be some added therapeutic benefit derived from a combination of DHAQ and radiation therapy.