Intra-arterial bromodeoxyuridine radiosensitization of malignant gliomas

Radiation Chemistry and Radiation Research: A History from the Beginning to the Platinum Edition

At the dawn of the 20th Century, the underlying chemistry that produced the observed effects of ionizing radiation, e.g., X rays and Radium salts, on aqueous solutions was either unknown or restricted to products found postirradiation. For example, the Curies noted that sealed aqueous solutions of Radium inexplicably decomposed over time, even when kept in the dark. By 1928 there were numerous papers describing the phenomenological effects of ionizing radiation on a wide variety of materials, including the irradiated hands of early radiologists. One scientist who became intensely interested in these radiation effects was Hugo Fricke (Fricke Dosimetry) who established a laboratory in 1928 dedicated to studies on chemical effects of radiation, the results of which he believed were necessary to understand observed radiobiological effects. In this Platinum Issue of Radiation Research (70 years of continuous publication), we present the early history of the development of radiation chemistry and its contributions to all levels of mechanistic radiobiology. We summarize its development as one of the four disciplinary pillars of the Radiation Research Society and its Journal, Radiation Research, founded during the period 1952-1954. In addition, the work of scientists who contributed substantially to the discipline of Radiation Chemistry and to the birth, life and culture of the Society and its journal is presented. In the years following 1954, the increasing knowledge about the underlying temporal and spatial properties of the species produced by various types of radiation is summarized and related to its radiobiology and to modern technologies (e.g., pulsed radiolysis, electron paramagnetic resonance) which became available as the discipline of radiation chemistry developed. A summary of important results from these studies on Radiation Chemistry/Biochemistry in the 20th and 21st Century up to the present time is presented. Finally, we look into the future to see what possible directions radiation chemistry studies might take, based upon promising current research. We find at least two possible directions that will need radiation chemistry expertise to ensure proper experimental design and interpretation of data. These are FLASH radiotherapy, and mechanisms underlying the effects of low doses of radiation delivered at low dose rates. Examples of how radiation chemists could provide beneficial input to these studies are provided.

Exosomal Plasminogen Activator Inhibitor-1 Induces Ionizing Radiation-Adaptive Glioblastoma Cachexia

Cancer cachexia is a muscle-wasting syndrome that leads to a severely compromised quality of life and increased mortality. A strong association between cachexia and poor prognosis has been demonstrated in intractable cancers, including glioblastoma (GBM). In the present study, it was demonstrated that ionizing radiation (IR), the first-line treatment for GBM, causes cancer cachexia by increasing the exosomal release of plasminogen activator inhibitor-1 (PAI-1) from glioblastoma cells. Exosomal PAI-1 delivered to the skeletal muscle is directly penetrated in the muscles and phosphorylates STAT3 to intensify muscle atrophy by activating muscle RING-finger protein-1 (MuRF1) and muscle atrophy F-box (Atrogin1); furthermore, it hampers muscle protein synthesis by inhibiting mTOR signaling. Additionally, pharmacological inhibition of PAI-1 by TM5441 inhibited muscle atrophy and rescued muscle protein synthesis, thereby providing survival benefits in a GBM orthotopic xenograft mouse model. In summary, our data delineated the role of PAI-1 in the induction of GBM cachexia associated with radiotherapy-treated GBM. Our data also indicated that targeting PAI-1 could serve as an attractive strategy for the management of GBM following radiotherapy, which would lead to a considerable improvement in the quality of life of GBM patients undergoing radiotherapy.

The use of radiosensitizing agents in the therapy of glioblastoma multiforme-a comprehensive review

BACKGROUND

Glioblastoma is the most common malignant brain tumor in human adults. Despite several improvements in resective as well as adjuvant therapy over the last decades, its overall prognosis remains poor. As a means of improving patient outcome, the possibility of enhancing radiation response by using radiosensitizing agents has been tested in an array of studies.

METHODS

A comprehensive review of clinical trials involving radiation therapy in combination with radiosensitizing agents on patients diagnosed with glioblastoma was performed in the National Center for Biotechnology Information's PubMed database.

RESULTS

A total of 96 papers addressing this matter were published between 1976 and 2021, of which 63 matched the subject of this paper. All papers were reviewed, and their findings discussed in the context of their underlining mechanisms of radiosensitization.

CONCLUSION

In the history of glioblastoma treatment, several approaches of optimizing radiation-effectiveness using radiosensitizers have been made. Even though several different strategies and agents have been explored, clear evidence of improved patient outcome is still missing. Tissue-selectiveness and penetration of the blood-brain barrier seem to be major roadblocks; nevertheless, modern strategies try to circumvent these obstacles, using novel sensitizers based on preclinical data or alternative ways of delivery.

Current Landscape and Future Prospects of Radiation Sensitizers for Malignant Brain Tumors: A Systematic Review

BACKGROUND

Radiation therapy (RT) is the cornerstone of management of malignant brain tumors, but its efficacy is limited in hypoxic tumors. Although numerous radiosensitizer compounds have been developed to enhance the effect of RT, progress has been stagnant. Through this systematic review, we provide an overview of radiosensitizers developed for malignant brain tumors, summarize their safety and efficacy, and evaluate areas for possible improvement.

METHODS

Following PRISMA guidelines, PubMed, EMBASE, Cochrane, and Web of Science were searched using terminology pertaining to radiosensitizers for brain tumor RT. Articles reporting clinical evidence of nonantineoplastic radiosensitizers with RT for malignant central nervous system tumors were included. Data of interest were presumed mechanism of action, median overall survival (OS), progression-free survival (PFS), and adverse events.

RESULTS

Twenty-two unique radiosensitizers were identified. Only 2/22 agents (fluosol with oxygen, and efaproxiral) showed improvement in OS in patients with glioblastoma and brain metastasis, respectively. A larger study was not able to confirm the latter. Improved PFS was reported with use of metronidazole, sodium glycididazole, and chloroquine. There was a wide range of toxicities, which prompted change of schedule or complete discontinuation of 9 agents.

CONCLUSIONS

Progress in radiosensitizers for malignant CNS tumors has been limited. Only 2 radiosensitizers have shown limited improvement in survival. Alternative strategies such as synthetic drug design, based on a mechanism of action that is independent of crossing the blood-brain barrier, may be necessary. Use of drug development strategies using new technologies to overcome past challenges is necessary.

In vivo Characterization of the Radiosensitizing Effect of a Very Low Dose of BrdU in Murine Cells Exposed to Low-Dose Radiation

The aim of the present study was to characterize the in vivo radiosensitizing effect of a very low dose of bromodeoxyuridine (BrdU) in mice exposed to low-dose radiation by establishing the following: (1) the radiosensitizing effect during DNA synthesis using single-cell gel electrophoresis (SCGE) in murine bone marrow cells, and (2) the number and timing of the mechanisms of genotoxicity and cytotoxicity, as well as the correlation of both end points, using flow cytometry analysis of the kinetics of micronucleus induction in reticulocytes. Groups of mice received intraperitoneal injections of 0.125 mg/g of BrdU 24 h prior to irradiation with 0.5 Gy of ⁶⁰ Co gamma rays. DNA breaks measured using SCGE were determined at 30 min after exposure to radiation. The kinetics of micronucleated reticulocyte (MN-RET) induction was determined every 8 h after irradiation up to 72 h. The results from both experimental models indicated that low-level BrdU incorporation into DNA increased the sensitivity to 0.5 Gy of radiation, particularly in the S phase. The formation of micronuclei by gamma rays was produced at three different times using two main mechanisms. In the BrdU-substituted cells, the second mechanism was associated with a high cytotoxic effect that was absent in the irradiated BrdU-unsubstituted cells. The third mechanism, in which micronucleus formation was increased in irradiated substituted cells compared with the irradiated nonsubstituted control cells, was also related to an increase in cytotoxicity. Environ. Mol. Mutagen. 60:534-545, 2019. © 2019 Wiley Periodicals, Inc.

Effects of resveratrol and methoxyamine on the radiosensitivity of iododeoxyuridine in U87MG glioblastoma cell line

The purpose of this study was to evaluate the combination effect of resveratrol and methoxyamine on radiosensitivity of iododeoxyuridine in spheroid culture of U87MG glioblastoma cell line using colony formation and alkaline comet assays. Spheroids on day-20 with 350 µm diameters were treated with 20 µM resveratrol and/or 6 mM methoxyamine and/or 1 µM iododeoxyuridine for one volume doubling time (67 h), and then irradiated with 2 Gy gamma-radiation ((60)Co) in different groups. After treatment, viability of the cells, colony forming ability and DNA damages were obtained by blue dye exclusion, colony formation and alkaline comet assay, respectively. Our results showed that methoxyamine and resveratrol could significantly reduce colony number and induce the DNA damages of glioblastoma spheroid cells treated with iododeoxyuridine in combination with gamma-rays. Therefore, methoxyamine as base excision repair inhibitor and resveratrol as hypoxia inducible factor 1-alpha inhibitor in combination with iododeoxyuridine as radiosensitizer enhanced the radiosensitization of glioblastoma spheroid cells.

Clinical significance of atomic inner shell ionization (ISI) and Auger cascade for radiosensitization using IUdR, BUdR, platinum salts, or gadolinium porphyrin compounds

PURPOSE

Halogenated pyrimidines (iododeoxyuridine [IUdR] and bromodeoxyuridine [BUdR]), platinum salts, and gadolinium porphyrins are heavy atom compounds used as radiosensitizers. For IUdR, it has been hypothesized that iodine inner shell ionizations (ISI) and Auger cascades could be one of the primary radiosensitization mechanisms. The purpose of this paper is to estimate the number of ISI produced per tumor cell and per 2 Gy irradiation in clinically relevant modelings.

MATERIALS AND METHODS

ISI were evaluated using a two-step method. Photon-induced ISI were calculated using the MCNP-4C Monte Carlo code, heavy atom concentrations from clinical data published in the literature, and at various depths in a water phantom irradiated with 6-MV, (60)Co, (137)Cs, or (192)Ir sources. Electron knock-on induced ISI on K, L, and M atomic shells were evaluated with an hybrid method, using simulated electron spectra and cross-sections derived from the Møller formalism. Using a biological dose equivalence of 0.05 Gy per cell ISI, relative biological effectiveness (RBE) values were calculated for each situation.

RESULTS

For platinum and gadolinium, ISI occurs in far less than 0.1% of the cell, whichever is the configuration. For IUdR and BUdR, ISI occurs in between 45% to 483% of the cell. Due to spectrum degradation, about 3 times more photoelectric ISI are generated at greater than shallower depths, and 10 times more for (192)Ir compared with (60)Co or 6-MV X-rays. Photoelectric ISI are about 3 times more frequent for iodine than bromine, but electron knock-on ISI are more frequent on bromine, and at the end about the same number of ISI are generated for both elements. RBEs were found to be between 1.01 and 1.12 for clinically relevant irradiation settings.

CONCLUSIONS

The mechanisms of radiosensitization for platinum and gadolinium are clearly not related to an Auger cascade. For halogenated pyrimidines, however, clinically relevant numbers of ISI are generated within each cell. For IUdR, ISI appears to be strongly tied to the photon spectra. Halogenated pyrimidines should be evaluated again clinically, but using lower energy photons like a (192)Ir implant.

Radiation chemistry and the Radiation Research Society: a history from the beginning

Radiation chemistry studies began in the early 20th century with observations involving the decomposition of various materials by X rays and radium. Hugo Fricke recognized that the chemical effects of radiation should be studied to help understand the response of living systems to radiation, and in 1928 he established a laboratory to conduct such studies. Early radiation chemists were intimately involved in the founding of the Radiation Research Society and contributed substantially to its interdisciplinary culture. In this historical review, the highlights of research in radiation chemistry leading up to the founding of the Radiation Research Society in 1952 are discussed. The status of the field is established at that point, and a sampling of the major accomplishments from then until the present is presented, with emphasis on those scientists who have contributed substantially to the life and culture of the Radiation Research Society.

IUdR polymers for combined continuous low-dose rate and high-dose rate sensitization of experimental human malignant gliomas

Local polymeric delivery enhances IUdR radiosensitization of human malignant gliomas (MG). The combined low-dose rate (LDR) (0.03 Gy/h) and fractionated high-dose rate (HDR) treatments result in cures of experimental MGs. To enhance efficacy, we combined polymeric IUdR delivery, LDR, and HDR for treatments of both subcutaneous and intracranial MGs. In vitro: Cells (U251 MG) were trypsinized and replated in triplicate 1 day prior to LDR irradiation in media either without (control) or with 10 microM IUdR. After 72 hr, LDR irradiation cells were acutely irradiated (1.1 Gy/min) with increasing (0, 1.25, 2.5, 5.0, or 10 Gy) single doses. Implantable IUdR polymers [(poly(bis(p-carboxyphenoxy)-propane) (PCPP): sebaic acid (PCPP:SA), 20:80] (50% loading; 10 mg) were synthesized. In vivo: For flank vs. intracranial tumors, mice had 6 x 10(6) subcutaneous vs. 2 x 10(5) intracranial cells. For intracranial or subcutaneous MGs, mice had intratumoral blank (empty) vs. IUdR polymer treatments. One day after implantation, mice had immediate external LDR (3 cGy/h x 3 days total body irradiation) or HDR (2 Gy BID x 4 days to tumor site) or concurrent treatments. For the in vitro IUdR treatments, LDR resulted in a striking increase in cell-killing when combined with HDR. For the in vivo LDR treatments of flank tumors, the growth delay was greater for the IUdR vs. blank polymer treatments. For the combined LDR and HDR, the IUdR treatments resulted in a dramatic decrease in tumor volumes. On day 60 the log V/V0 were -1.7 +/- 0.22 for combined LDR + HDR + IUdR polymer (P < 0.05 vs. combined LDR + HDR + blank polymer). Survival for the intracranial controls was 22.9 +/- 1.2 days. For the blank polymer + LDR vs. blank polymer + LDR + HDR treatments, survival was 25.3 +/- 1.7 (P = NS) vs. 48.1 +/- 3.5 days (P < 0.05). For IUdR polymer + LDR treatment survival was 27.3 +/- 2.3 days (P = NS). The most striking improvement in survival followed the IUdR polymer + LDR + HDR treatment: 66.0 + 6.4 days (P < 0.05 vs. blank polymer + LDR + HDR). The polymeric IUdR delivery plus combined continuous LDR and HDR treatments results in growth delay and improved survival in animals bearing the MG xenografts. This treatment may hold promise for the treatment of human MGs.

Synthetic, implantable polymers for local delivery of IUdR to experimental human malignant glioma

PURPOSE

Recently, polymeric controlled delivery of chemotherapy has been shown to improve survival of patients with malignant glioma. We evaluated whether we could similarly deliver halogenated pyrimidines to experimental intracranial human malignant glioma. To address this issue we studied the in vitro release from polymers and the in vivo drug delivery of IUdR to experimental human U251 glioblastoma xenografts.

METHODS AND MATERIALS

In vitro: To measure release, increasing (10%, 30%, 50%) proportions of IUdR in synthetic [(poly(bis(p-carboxyphenoxy)-propane) (PCPP):sebacic acid (SA) polymer discs were serially incubated in buffered saline and the supernatant fractions were assayed. In vivo: To compare local versus systemic delivery, mice bearing flank xenografts had intratumoral or contralateral flank IUdR polymer (50% loading) treatments. Mice bearing intracranial (i.c.) xenografts had i.c. versus flank IUdR polymer treatments. Four or 8 days after implantation of polymers, mice were sacrificed and the percentage tumor cells that were labeled with IUdR was measured using quantitative microscopic immunohistochemistry.

RESULTS

In vitro: Increasing percentage loadings of IUdR resulted in higher percentages of release: 43.7 + 0.1, 70.0 + 0.2, and 90.2 + 0.2 (p < 0.001 ANOVA) for the 10%, 30%, and 50% loadings, respectively. In vivo: For the flank tumors, both the ipsilateral and contralateral IUdR polymers resulted in similarly high percentages labeling of the tumors versus time. For the ipsilateral IUdR polymers, the percentage of tumor cellular labeling after 4 days versus 8 days was 45.8 +/- 7.0 versus 40.6 +/- 3.9 (p = NS). For the contralateral polymer implants, the percentage of tumor cellular labeling were 43.9 +/- 10.1 versus 35.9 +/- 5.2 (p = NS) measured 4 days versus 8 days after implantation. For the i.c. tumors treated with extracranial IUdR polymers, the percentage of tumor cellular labeling was low: 13.9 +/- 8.8 and 11.2 +/- 5.7 measured 4 and 8 days after implantation. For the i.c. tumors having the i.c. IUdR polymers, however, the percentage labeling was comparatively much higher: 34.3 +/- 4.9 and 35.3 +/- 4.0 on days 4 and 8, respectively. For the i.c. tumors, examination of the percentage cellular labeling versus distance from the implanted IUdR polymer showed that labeling was highest closest to the polymer disc.

CONCLUSION

Synthetic, implantable biodegradable polymers provide the local, controlled release of IUdR and result in the high, local delivery of IUdR to experimental intracranial human malignant glioma. This technique holds promise for the local delivery of IUdR for radiosensitization of human brain tumors.

Apoptosis and p53 expression in human gliomas

Twenty-five human gliomas of different histological grade and type were studied for p53 expression by immunohistochemistry and for apoptosis using ApopTag method. p53 expression (percentage of positive cells) was highest in anaplastic astrocytomas, followed by low grade astrocytomas and surprisingly in glioblastomas. Granular cytoplasmic p53 positivity appeared in 4/5 low grade oligodendroglioma and in 2/5 low grade mixed oligoastrocytomas. The means of apoptosis index in the different tumor types ranged between 0.8 and 11.5 with the highest values in anaplastic astrocytoma and glioblastomas. Although the number of cases per group were relatively low and the individual vales showed differences it seems that p53 expression is related to the biological aggressiveness of gliomas. It is also suggested that high level of apoptosis in malignant glioma could represent a p53 independent pathway.

A phase I trial of hepatic arterial bromodeoxyuridine and conformal radiation therapy for patients with primary hepatobiliary cancers or colorectal liver metastases

PURPOSE

We have previously found that conformal radiation therapy (RT) and hepatic arterial fluorodeoxyuridine was associated with durable responses and long-term survival for patients treated for nondiffuse primary hepatobiliary tumors and colorectal liver metastases. Further improvements in hepatic control may result from the addition of selective radiosensitization using bromodeoxyuridine (BrdU) infused through the hepatic artery (HA) concurrently with RT. This is a Phase I study of escalating doses of HA BrdU combined with our standard hepatic RT.

METHODS AND MATERIALS

Patients with unresectable primary hepatobiliary cancer or colorectal liver metastases were treated with concurrent HA BrdU and conformal RT (1.5 Gy per fraction, twice a day). Three-dimensional treatment planning was used to define both the target and normal liver volumes. The total dose of RT (24, 48, or 66 Gy) was determined by the fractional volume of normal liver excluded from the high dose volume. HA BrdU was escalated in standard Phase I fashion with at least three patients receiving each combination of RT dose and BrdU dose. The starting dose of HA BrdU was 10 mg/kg/day, with two potential escalations to a maximum of 25 mg/kg/day (the maximum tolerable dose of HA BrdU when given alone on this same schedule). Grade > or = 3 toxicity was considered dose limiting. Patients receiving 24 Gy had one cycle of HA BrdU, while those receiving either 48 or 66 Gy had two cycles. Patients were followed for toxicity, complications, and response (when evaluable).

RESULTS

A total of 41 patients (18 with colorectal liver metastases, 16 with cholangiocarcinoma and 7 with hepatoma) were treated. Five patients were removed from the protocol (three had HA catheter complications, one developed atrial fibrillation, and one was removed due to recurrent Grade 4 toxicity), although all five are included for toxicity purposes. Dose-limiting toxicity was primarily thrombocytopenia and there was no obvious relationship with the RT dose. Only 2 of 17 cycles given at 25 mg/kg/day had Grade > or = 3 toxicity. Complications developed in four patients, including one patient with radiation-induced liver disease. Response rates were not improved compared to our previous experience.

CONCLUSIONS

The appropriate dose of HA BrdU for Phase II evaluation is 25 mg/kg/day. Neither the hepatic parenchyma nor the gastrointestinal mucosa appeared to be sensitized by this method of BrdU administration. It is anticipated that these, or still newer methods of therapy, can improve treatment results in the near future.

In vivo determination of 5-bromo-2'-deoxyuridine incorporation into DNA tumor tissue by a new 32P-postlabelling thin-layer chromatographic method

The halopyrimidine 5-bromo-2'-deoxyuridine (BUDR) can serve as one of many indicators of tumor malignity, complementary to histologic grade. We have developed a thin-layer chromatographic (TLC) technique that can assess tumor DNA base composition and analogue (BUDR) incorporation which vies with immunochemistry for BUDR. This requires post-labeling DNA by nick-translation and radioactive 5'-phosphorylation of representative 32P-alpha-dNMPs (deoxynucleotide monophosphates). Subsequent 3'-monophosphate digest exchanges a radioactive 32PO4 for the neighboring cold nucleotide. Separation in two dimensional PEI-cellulose TLC is carried out in acetic acid, (NH4)2SO4, and (NH4)HSO4. TLC of dNMPs was applied to control HeLa DNA, and HeLa cells receiving BUDR. BUDR is detected in 10(6) HeLa cells after 12-72 h incubations. Findings in HeLa DNA demonstrate normal TLC retention factors for all 32P-dNMPs. Two dimensional R(F) (x,y axes in cm) demonstrate: dAMP=1.4, 9.4; dCMP=10.0, 13.5; dGMP=4.6, 4.4; dTMP=9.0, 7.4; and BUDRMP 6.4, 6.6. This technique quantifies BUDR--which parallels tumor S phase, and serves as an indicator of labelling index (LI).

Implantable biodegradable polymers for IUdR radiosensitization of experimental human malignant glioma

PURPOSE

The potential of halogenated pyrimidines for the radiosensitization of human malignant gliomas remains unrealized. To assess the role of local delivery for radiosensitization, we tested a synthetic, implantable biodegradable polymer for the controlled release of 5-iodo-2'-deoxyuridine (IUdR) both in vitro and in vivo and the resultant radiosensitization of human malignant glioma xenografts in vivo.

MATERIALS AND METHODS

In vitro: To measure release, increasing (10%, 30%, 50%) proportions (weight/weight) of IUdR in the polyanhydride [(poly(bis(p-carboxyphenoxy)-propane) (PCPP): sebacic acid (SA) (PCPP : SA ratio 20:80)] polymer discs were incubated (1 ml phosphate-buffered saline, 37 degrees C). The supernatant fractions were serially assayed using high performance liquid chromatography. To measure modulation of release, polymer discs were co-loaded with 20 microCi 5-125-iodo-2'-deoxyuridine (125-IUdR) and increasing (10%, 30%, or 50%) proportions of D-glucose. To test radiosensitization, cells (U251 human malignant glioma) were sequentially exposed to increasing (0 or 10 microM) concentrations of IUdR and increasing (0, 2.5, 5.0, or 10 Gy) doses of acute radiation. In vivo. To measure release, PCPP : SA polymer discs having 200 microCi 125-IUdR were surgically placed in U251 xenografts (0.1-0.2 cc) growing in the flanks of nude mice. The flanks were reproducibly positioned over a collimated scintillation detector and counted. To measure radiosensitization, PCPP : SA polymer discs having 0% (empty) or 50% IUdR were placed in the tumor or contralateral flank. After five days, the tumors were acutely irradiated (500 cGy x 2 daily fractions).

RESULTS

In vitro: Intact IUdR was released from the PCPP : SA polymer discs in proportion to the percentage loading. After 4 days the cumulative percentages of loaded IUdR that were released were 43.7 +/- 0.1, 70.0 +/- 0.2, and 90.2 +/- 0.2 (p < 0.001 ANOVA) for the 10, 30, and 50% loadings. With 0, 10, 30, or 50% D-glucose co-loading, the cumulative release of 125-IUdR from PCPP : SA polymers was 21, 70, 92, or 97% (p < 0.001), respectively, measured 26 days after incubation. IUdR radiosensitized U251 cells in vitro. Cell survival (log10) was -2.02 +/- 0.02 and -3.68 +/- 0.11 (p < 0.001) after the 10 Gy treatment and no (control) or 10 microM IUdR exposures, respectively. In vivo: 125-IUdR Release: The average counts (log10 cpm +/- SEM) (hours after implant) were 5.2 +/- 0.05 (0.5), 4.3 +/- 0.07 (17), 3.9 +/- 0.08 (64), and 2.8 +/- 0.06 (284). Radiosensitization: After intratumoral implantation of empty polymer or intratumoral 50% IUdR polymer, or implantation of 50% IUdR polymers contralateral to tumors the average growth delays of tumors to 4 times the initial volumes were 15.4 +/- 1.8, 20.1 + 0.1, and 20.3 + 3.6 (mean + SEM) days, respectively (p = 0.488 one-way ANOVA). After empty polymer and radiation treatments, no tumors regressed and the growth delay was 31.1 + 2.1 (p = 0.046 vs. empty polymer alone) days. After implantation of 50% IUdR polymers either contralateral to the tumors or inside the tumors, followed by radiation, tumors regressed; growth delays to return to the initial average volumes of 14.0 + 3.6 or 24.2 + 0.2 (p < 0.01) days, respectively.

CONCLUSIONS

Synthetic, implantable biodegradable polymers hold promise for the controlled release and local delivery of IUdR for radiosensitization of gliomas.

A phase I trial of intravenous bromodeoxyuridine and radiation therapy for pancreatic cancer

PURPOSE

Improved radiosensitization may lead to improved results of treatment for pancreatic cancer. This Phase I trial was designed to determine the maximum tolerable dose of intravenous bromodeoxyuridine (BrdUrd) when given in an alternating weekly fashion with radiation therapy for patients with pancreatic cancer.

METHODS AND MATERIALS

Patients with resected or locally unresectable pancreatic cancer were eligible if distant metastases were not present. A continuous intravenous infusion of BrdUrd was given on weeks 1, 3, 5, and 7. Twice a day radiation therapy (1.5 Gy per fraction) was given on weeks 2, 4, 6, and 8 to the pancreas/pancreatic bed (total dose 60 Gy) and draining regional lymph nodes (total dose 45 Gy). The starting dose of BrdUrd was 800 mg/m2/day with a planned escalation to 1000 mg/m2/day if at least six out of eight patients were without Grade > or = 3 toxicity. Patients were assessed weekly for toxicity, and were followed every 3 months after treatment for complications and survival.

RESULTS

Fifteen patients with resected (six) or unresectable (nine) pancreatic cancer were enrolled. One patient failed to complete therapy due to tumor progression. One of 11 patients treated with 800 mg/m2/day had a Grade 3 toxicity, while Grade 3 or 4 toxicity was found in all 3 patients receiving 1000 mg/m2/day. The dose-limiting toxicities were hematologic. The acute gastrointestinal toxicity was minimal. Two patients, including one with unresectable disease, were without evidence of disease during exploration for complications (ulcer, small bowel obstruction).

CONCLUSIONS

The recommended dose of BrdUrd for Phase II study is 800 mg/m2/day. The gastrointestinal mucosa did not appear to be sensitized by this method of BrdUrd administration. The presence of a pathologic complete response is encouraging. Further improvements in radiosensitization are possible and may lead to improved local control.

Preclinical studies of chemotherapy and radiation therapy for pancreatic carcinoma

The use of radiation therapy combined with 5-fluorouracil (5-FU) in the treatment of pancreatic cancer has been well established. It has been hypothesized that any benefit from combined 5-FU and radiation has been due to radiosensitization. Improved therapy could result from a better understanding of the mechanism of radiosensitization and the development of compounds capable of providing better radiosensitization. This article reviews preclinical findings on the mechanism of cytotoxicity and radiosensitization for 5-FU, fluorodeoxyuridine, thymidine analogs, and gemcitabine (2',2'-difluorodeoxycytidine) and discusses the clinical implications of these findings.

Effect of irradiation on bromodeoxyuridine incorporation in human colon cancer xenografts

PURPOSE

Although we have characterized the incorporation of the thymidine analog bromodeoxyuridine (BrdUrd) into human colon cancer xenografts under a wide variety of conditions, little is known about the effect of radiation on subsequent incorporation. Because clinical protocols include, as one component, BrdUrd administration after radiation, it was important to confirm that irradiation did not prevent subsequent BrdUrd incorporation. Therefore, we studied the effect of irradiation on BrdUrd incorporation into HT29 human colon cancer xenografts.

METHODS AND MATERIALS

Two types of experiments were performed. In the first, the effect of radiation on subsequent incorporation was measured. Tumors received doses of 0, 2, 8, and 12 Gy, animals were infused with BrdUrd for 4 days, and incorporation was assessed at the end of the infusion. In the second, the effect of radiation on the elimination of BrdUrd from tumors was determined. Animals were infused with BrdUrd, tumors were irradiated with either 0 or 12 Gy, and tumor incorporation of BrdUrd was measured 1 and 3 days later.

RESULTS

Radiation affected neither the incorporation into nor the elimination of BrdUrd from human tumor xenografts.

CONCLUSIONS

These findings support the feasibility of clinical trials interdigitating BrdUrd infusion and radiation.

Radiation therapy and bromodeoxyuridine chemotherapy followed by procarbazine, lomustine, and vincristine for the treatment of anaplastic gliomas

PURPOSE

To conduct a Phase II study to evaluate the long-term efficacy and safety of radiotherapy combined with intravenous bromodeoxyuridine for patients with anaplastic glioma tumors.

METHODS AND MATERIALS

Between 1983 and 1987, study patients received 1.7-1.8 Gy radiation once a day, Monday through Friday, to a total dose of 60 Gy. On the Thursday prior to beginning radiotherapy and for the next 5 weeks (6 weeks total), patients received a continuous 96 h intravenous infusion of bromodeoxyuridine at 0.8 g/m2/24 h; following radiotherapy, patients received procarbazine, lomustine (CCNU), and vincristine (PCV) for 1 year or until tumor progressed.

RESULTS

One-hundred thirty eight patients (median age, 43 years) were evaluable for analysis. Estimated 4-year survival for the anaplastic astrocytoma (AA) stratum (n = 116) is 46%. For the astrocytoma (ASTRO) stratum (n = 22), the 6-year survival is estimated at 79%. Estimated 4-year progression-free survival for AAs is 42%, and for ASTROs, 68%. Whole brain irradiation was used in 23% and limited-field irradiation in 77%; patients receiving limited-field irradiation had a better survival rate (p = 0.07). Total tumor resection was performed in 15%, partial resection in 53%, and biopsy only in 32%. For the 81 patients with tumor recurrence, 34 (42%) are known to have received additional treatment(s). For AA, fits of the Cox proportional hazards regression model showed that covariates individually predictive of survival were younger age (p < 0.001), Karnofsky performance score (p = 0.10). Major toxicities were rash during Weeks 1 through 6 requiring dose modification in 14%, Grade > or = III leukopenia in 18%, and Grade > or = III thrombocytopeni in 9%.

CONCLUSION

The study suggests that the bromodeoxyuridine-radiotherapy-PCV, compared with other published therapies, can improve progression-free survival, and aggressive treatment of ASTRO patients can lead to substantial increases in survival compared to published survival data.

Stereotactic radiosurgery for glioblastoma: a final report of 31 patients

From February 1989 to December 1992, 31 patients who presented with an initial pathological diagnosis of glioblastoma multiforme underwent tumor debulking or biopsy, stereotactic radiosurgery, and standard radiation therapy as part of their primary treatment. Presenting characteristics in the 22 men and nine women included a median age of 57 years, Karnofsky Performance Scale score median of 80, and median tumor volume of 16.4 cm3. Stereotactic radiosurgery delivered a central dose of 15 to 35 Gy with the isocenter location, collimator size, and beam paths individualized by means of three-dimensional software developed at the University of Wisconsin. The peripheral isodose line varied from 40% to 90% with a median of 72.5% and a mode of 80%. The mean follow-up period was 12.84 months with a median of 9.5 months. Statistical analysis was performed using Kaplan-Meier analysis and log-rank comparison of risk factor groups. The parameters of age, initial Karnofsky Performance Scale score, and biopsy were significantly different in patient survival from debulking; but no difference was noted between single and multiple isocenters and patterns of steroid requirement. Radiographic recurrences were divided by location into the following categories: central (within central stereotactic radiosurgery dose), 0; peripheral (within 2 cm of central dose), 19; and distant (> 2 cm), 4. There is no evidence of recurrence in five surviving patients. Actuarial 12-month survival was 37%, with a median survival of 9.5 months. These values are similar to previous results for surgery and standard radiotherapy alone. The results suggest that the curative value of radiosurgery is significantly limited by peripheral recurrences.

Azidothymidine (AZT) as a potential modifier of radiation response in vitro

The potential effect of AZT as a thymidine analogue on radiation response in vitro was investigated. Two human cell lines (WiDr and HeLa) were used. The effect of 10 microM AZT on exponentially growing cells was studied after different exposure times (24, 48 and 72 h). The surviving fraction (clonogenic assay) or metabolic activity (MTT assay) after irradiation of AZT-exposed cells, was compared to unexposed irradiated controls. Flow cytometry was used to assess the cell-cycle effect of pre-exposure of exponentially growing cells to AZT. AZT had a radioprotective effect for all experimental time points as far as WiDr was concerned. For HeLa the effect was significant at 24 h. Cell-cycle analysis showed a significant accumulation in S-phase at 72 h for WiDr. For HeLa there was a significant accumulation in S-phase at 48 h. We conclude that under the reported experimental conditions, AZT as a thymidine analogue seems to reduce the cytotoxic effect of irradiation.

National Cancer Institute (phase II) study of high-grade glioma treated with accelerated hyperfractionated radiation and iododeoxyuridine: results in anaplastic astrocytoma

PURPOSE

We report the outcome of a Phase II study of a cohort of patients with high-grade glioma treated with accelerated hyperfractionated radiation and the radiation sensitizer, iododeoxyuridine (IdUrd).

METHODS AND MATERIALS

Between January 1988 and December 1990, 39 consecutive patients with high-grade glioma were enrolled and treated on a Phase II protocol including hyperfractionated radiation and IdUrd. Thirty-two patients were male and seven were female. Age range was 19 to 71 years with a median age of 38 years. IdUrd (1000 mg/m2 per day) was administered in two separate 14-day courses, the first during the initial radiation field and the second during the final cone-down field. All patients were treated consistently with partial brain technique and received 1.5 Gy/fraction twice daily to a mean total dose of 71.25 Gy (range 66-72 Gy excluding one patient who did not complete treatment). The initial field was treated to 45 Gy followed by a cone-down field covering the tumor volume plus a 1-cm margin to the final dose. Patients were assessed for acute and long-term morbidity and followed for outcome. Two patients had biopsies during the course of treatment. Flow cytometry and high performance liquid chromatography was used to evaluate the labeling index and the percent replacement of IdUrd in the biopsy specimen.

RESULTS

Thirty-eight of 39 patients completed therapy. One patient died on treatment at 48 Gy and is included in the survival analysis. No patient was lost to follow-up. Twenty-one patients had Grade 3 (anaplastic astrocytoma) tumors and 18 patients had Grade 4 (glioblastoma multiforme). Median survival for the entire cohort was 23 months. For the glioblastoma multiforme patients, median survival was 15 months. The median survival of the anaplastic astrocytoma patients has not yet been reached. In the patients assessed, the range of IdUrd tumor cell incorporation was only 0-2.4%.

CONCLUSION

Accelerated hyperfractionated radiation therapy with IdUrd was administered with acceptable acute toxicity. The major acute side effects of mucositis and thrombocytopenia were related to IdUrd infusion and were dose-dependent. There were no unacceptable acute toxicities referable to the radiation as delivered. With a median potential follow-up of 51 months, the actuarial median survival of the glioblastoma multiforme patients is comparable with the best previously published reports. The outcome of patients with anaplastic astrocytoma compares very favorably with even the most aggressive multi-modality approaches in the recent literature with a minimum of acute morbidity.

Kinetics of cell labeling and thymidine replacement after continuous infusion of halogenated pyrimidines in vivo

PURPOSE

Iododeoxyuridine (IdUrd) is a halogenated pyrimidine which has been recognized as a clinical radiosensitizer. It is generally agreed that the extent of radiosensitization correlates with the degree of thymidine substitution in DNA. Controversy exists regarding the optimal administration schedule to achieve maximum radiosensitization. To obtain more information relating to this problem, we present experiments on an in vivo human tumor xenograft continuously exposed to a fixed serum concentration of halogenated pyrimidines so as to study the kinetics of cell labeling and thymidine replacement.

METHODS AND MATERIALS

Human colon tumor (HCT-116) cells were injected subcutaneously into nude mice. After 10 days, most animals (> 90%) developed measurable tumor nodules with a volume doubling time of 5 +/- 1 days. Once the tumors reached a cross-sectional area of 0.25-0.30 cm2, miniosmotic pumps were implanted to deliver a dose of 100 mg/kg/day of IdUrd by continuous infusion. After an IdUrd exposure time of 1-7 days, blood and tumor tissue were collected.

RESULTS

The steady state serum IdUrd concentration was 0.95 +/- 0.1 microM, which is a clinically relevant concentration for a prolonged continuous intravenous infusion. The tumor cell potential doubling time (Tpot) was 25 +/- 2 h. The percent IdUrd thymidine replacement and the fraction of cells labeled, followed exponential saturation kinetics with a halflife of 33 +/- 9 and 27 +/- 2 h, respectively. After 5 days of exposure (congruent to 5 x Tpot), the thymidine replacement in tumor cells was 2.0 +/- 0.2% and the fraction of tumor cells labeled was 94 +/- 1%. Immunohistochemical staining of IdUrd labeled tumor tissues showed an exposure dependent gradient of cellular labeling that was initially highest in regions close to blood vessels. After 4 days of exposure at 100 mg/kg/day, there was an increase in the fraction of cells in G(0) + G1 and a decrease in the S phase population, suggesting a block between G1 and S phase.

CONCLUSION

We conclude that the in vivo kinetics of IdUrd thymidine replacement and fraction of cells labeled after continuous exposure followed exponential saturation kinetics with a halflife of approximately the potential doubling time of the tumor cell population. Simple modeling suggests that some form of prolonged, or briefly interrupted, continuous infusion should be considered for clinical administration because such schedules would leave fewer cells unsensitized than shorter infusions would. Even 10% of unlabeled clonogenic cells could explain the lack of dramatic clinical successes with IdUrd or BrdUrd sensitization.

The application of 5-bromodeoxyuridine in the management of CNS tumors

A variety of clinical reports have described the application of the bromodeoxyuridine labeling index as an adjunct to conventional pathological examination of CNS tumors. This index has proven useful in predicting the clinical outcome associated with many such tumors. Furthermore, because of its efficacy as a radiosensitizing agent, bromodeoxyuridine (and the closely related iododeoxyuridine) has been used in combination with radiation therapy for malignant glial neoplasms, with some encouraging results. Although most studies suggest that bromodeoxyuridine is safe, there is evidence that this compound does have potential side-effects, including the observation that it is a mutagen and carcinogen in some experimental systems. A number of new alternative approaches for predicting the clinical outcome of CNS tumors has been developed based on an increased understanding of their molecular biology. However, until such approaches are better characterized, the clinical application of bromodeoxyuridine will continue to play an important role in predicting the clinical behavior of many CNS tumors.

Iododeoxyuridine (IUdR) combined with radiation in the treatment of malignant glioma: a comparison of short versus long intravenous dose schedules (RTOG 86-12)

PURPOSE

To evaluate the toxicity and tumor efficacy of the halopyrimidine IUdR (NSC #39661, IND 22475) as a chemical modifier of radiation response when used in a high dose short time infusion versus the acceptable 4 day infusion.

METHODS AND MATERIALS

In August 1987 we initiated a prospective study in patients with newly diagnosed anaplastic astrocytoma and glioblastoma. The study was designed to have a fixed dose of radiation (60.16 Gy = 1.88 Gy in 32 fractions in 6.5 weeks) but varying the dose schedule of IUdR, keeping the total dose between 21 and 24 g/m2. IUdR was delivered in a 96, 48, or 24 hr continuous intravenous infusion per week for 6.5 weeks during radiation treatment.

RESULTS

The study was closed for patient accrual on October 1, 1991. Twenty-two patients were treated on the 96 hrs, 32 on the 48 hr and 25 on the 24 hr schedules. The incidence of glioblastoma ranged between 68 and 75% in the three arms. Seventy percent of the patients had a Karnofsky of 80-90% at the onset of treatment. Over 50% of the patient population were under age 55. Drug tolerance was related to the duration of the IUdR infusion. Toxicities were most pronounced in the 96 hr IUdR infusion schedule where 27.4% of the patients reported a grade 3 drug toxicity. No fatal or grade 4 toxicities were observed. More patients on the 24 and 48 hr schedule received at least 80% of the IUdR dose specified per protocol. We did not observe a trend in acute normal tissue radiation reactions in any of the three arms. The median survivals calculated from the Kaplan-Meier plot are 13.4, 10.5, and 11 months, respectively, for the 96, 48, and 24 hr infusions. The Cox Proportional Hazards model showed that any difference in survival can be attributed to histological grade, type of previous surgery and, to some extent, age of the patient. Dose schedule was not a significant predictor of survival, although statistically nonsignificant trend toward longer survival is seen in those patients with glioblastoma treated in the "long" 4 day schedule.

CONCLUSION

Overall, our treatment combination, particularly for patients with glioblastoma, has not shown convincing evidence of an improvement in survival. Of interest, however, it is the 2 year survival rate of 68% for patients with anaplastic astrocytoma. In our experience, the administration of IUdR is laborious, time consuming and with bothersome acute gastrointestinal and hematological toxicities.

The clinical rationale for S-phase radiosensitization in human tumors

Nonhypoxic cell radiosensitizers, principally the halogenated pyrimidines and hydroxyurea, have been studied in the laboratory and clinical setting for more than 30 years. Early clinical experience in the 1960s and 1970s with the thymidine analogs 5-bromodeoxyuridine (BUdR) and 5-iododeoxyuridine (IUdR) was disappointing because normal tissue toxicity eliminated any potential for therapeutic gain. Inadequate delivery systems for intravenous and intraarterial infusions also contributed to the decline of this strategy. More recently, laboratory investigations have revealed further information regarding the mechanism of IUdR/BUdR radiosensitization. This knowledge provided a rationale for the sequence and timing of drug and radiation exposure, which could be both effective and tolerable. Advancing technology also provided safer infusion devices, and a resurgence in clinical trials combining IUdR or BUdR and radiation resulted. Current laboratory studies are now providing data on tumor cell kinetics, which is being applied to ongoing clinical trials. Fluoropyrimidines, principally 5-fluorouracil (5-FU), were also used in early clinical trials and unlike IUdR/BUdR were found to have significant activity as single agents against a variety of tumor types. The clinical integration of 5-FU and radiation occurred more slowly, but recent trials have demonstrated a therapeutic gain. Improved rates of local control and survival with combined 5-FU and radiation versus radiation alone have now been demonstrated in patients with rectal, esophageal, and anal carcinomas. However, the mechanism of interaction between the fluoropyrimidines and radiation remains uncertain and continues to be investigated with the hope of improved clinical outcome. As the cellular pathways influenced by the halogenated pyrimidines have been defined, the potential for biochemical modulation of these agents has been recognized. Leucovorin, the most commonly applied modulator, has been shown to enhance the activity of 5-FU in patients with metastatic colorectal carcinoma. These studies serve as an example for current trials that use biochemical modulators of IUdR, BUdR, and 5-FU as radiosensitizers. Hydroxyurea, currently used in the treatment of chronic leukemia, has also been considered a radiosensitizer. As with IUdR/BUdR, the clinical trials have often been inconclusive and interest in this radiosensitizer has waned. A poor understanding of the mechanism of action and tumor cell/normal tissue kinetics may be responsible for the lack of overall success with this strategy. Current investigations of cell kinetics in humans and potential mechanisms of hydroxyurea action could provide information critical to future trials of hydroxyurea radiosensitization.

Radiation therapy for malignant astrocytomas in adults

High grade (or malignant) astrocytomas remain a formidable therapeutic challenge. The main prognostic factors are patient age, patient performance status, tumor grade, the extent of surgical resection and the presence of fits. These factors could help to identify different groups of patients and should be an advantage in deciding on treatment strategies. Modern imaging techniques provide a more precise idea of tumor volume. The study of tumor recurrence shows that they occur in the immediate vicinity of the primary site. Surgery aside, radiotherapy remains the most important treatment modality. Currently, its standards concerning optimal dose and target volume appear to be accepted overall. There is no doubt that a dose-response relation exists; however, doses exceeding 60 Gy increase morbidity. Therefore 60 Gy is the dose most often cited in the literature. Furthermore, as whole brain irradiation does not decrease the risk of recurrence, a focal irradiation including a defined mean volume is generally used today. Radiosensitizers and heavy particles have not fulfilled their initial promise. Brachytherapy remains an interesting alternative for a limited number of patients. Nevertheless, it seems to increase recurrence at a distance from the primary site and to lead to severe focal lesions. Interstitial thermoradiotherapy may minimize local doses and thus help avoid serious local necrosis. Amongst the other therapeutic alternatives, intravenous chemotherapy using nitrosoureas provides a certain but modest benefit. Other administration modalities are currently undergoing evaluation. These include intra-arterial chemotherapy or high dose chemotherapy with auto-bone marrow transplantation. The interest of this latter is concerned mainly with anaplastic astrocytomas. Finally, among the future alternatives, gene therapy appears to hold the most promise. Intensive therapies, combined modality treatments, with the recent help of biological innovations, should be proposed to favorable groups of patients.

A quantitative assessment of the addition of MRI to CT-based, 3-D treatment planning of brain tumors

Quantitative 3-D volumetric comparisons were made of composite CT-MRI macroscopic and microscopic tumor and target volumes to their independently defined constituents. Volumetric comparisons were also made between volumes derived from coronal and axial MRI data sets, and between CT and MRI volumes redefined at a repeat session in comparison to their original definitions. The degree of 3-D dose coverage obtained from use of CT data only or MRI data only in terms of coverage of composite CT-MRI volumes was also analyzed. On average, MRI defined larger volumes as well as a greater share of composite CT-MRI volumes. On average, increases in block margin on the order of 0.5 cm would have ensured coverage of volumes derived from use of both imaging modalities had only MRI data been used. However, the degree of inter-observer variation in volume definition is on the order of the magnitude of differences in volume definition seen between the modalities, and the question of which imaging modality best describes tumor volumes remains unanswered until detailed histologic studies are performed. Given that tumor volumes independently apparent on CT and MRI have equal validity, composite CT-MRI input should be considered for planning to ensure precise dose coverage for conformal treatments.

Decrease in TTP pools mediated by 5-bromo-2'-deoxyuridine exposure in a human glioblastoma cell line

The antitumor and radiosensitizing properties of 5-bromo-2'-deoxyuridine (BUdR) appear to be due, in part, to its incorporation into cellular DNA. To optimize conditions for incorporation of 5-bromo-2'-deoxyuridine-5'-monophosphate (BrdUMP) into DNA, we investigated the metabolism of BUdR to its DNA precursor form, the 5'-triphosphate BrdUTP, in the U251 human glioblastoma cell line. The results demonstrated that BrdUTP accumulated rapidly in this cell line, achieving steady-state values within 2 hr of drug addition. The level of BrdUTP accumulation was proportional to the amount of exogenous BUdR up to a concentration of 100 microM, without apparent saturation. Exposure of glioblastoma cells to BUdR was associated with substantial selective decreases in both the cellular dCTP and TTP pools, the extent of which was dependent on the exogenous BUdR concentration. In the absence of exogenous BUdR, BrdUTP was eliminated rapidly from cells with an initial half-life of approximately 15 min. As the cellular BrdUTP level declined, the dCTP and TTP levels increased to control values. Incorporation of BrdUMP into DNA appeared linear with time as long as the cellular BrdUTP level remained constant. This incorporation was not enhanced by the addition of 5-fluoro-2'-deoxyuridine (FUdR), a potent inhibitor of thymidylate synthetase, which at a concentration of 10 nM had no effect on TTP pools in this cell line. Thus, the decrease in cellular TTP pools mediated by BrdUTP allows the halogenated pyrimidine to enhance its own incorporation into DNA.

Modulation of iododeoxyuridine-mediated radiosensitization by 5-fluorouracil in human colon cancer cells

The incorporation of 5-iodo-2'-deoxyuridine (IdUrd), a thymidine analog radiosensitizer, can be increased by the use of modulators such as 5-fluorouracil (FUra). FUra is a particularly attractive potential modulator to use against colorectal cancer, as it is the most active single agent in the treatment of this disease. To begin to define the conditions for the optimal combination of IdUrd and FUra in the treatment of patients with colorectal cancer, a study was conducted of the effect of FUra on IdUrd-mediated radiosensitization in cultured HT29 human colon cancer cells. It was found that when cells were exposed to concentrations of IdUrd typical of those obtained through intravenous exposure (1-3 microM), FUra (1 microM) increased radiosensitization beyond that which would be predicted for the same extent of incorporation produced by incubation with IdUrd alone. This increase appeared to result from a combination of at least two effects: FUra-mediated cell cycle redistribution and increased IdUrd incorporation. When a higher concentration of IdUrd (10 microM) was used with FUra (1 microM), cell cycle distribution returned to nearly normal, and radiosensitization was equal to that predicted by the extent of incorporation of IdUrd. These data demonstrate that the combination of FUra and IdUrd can produce radiosensitization both through increased IdUrd incorporation and cell cycle redistribution. Furthermore, they suggest that, in the presence of a modulator, it may not be necessary to achieve high levels of IdUrd incorporation to produce significant tumor radiosensitization.

Measurement of incorporation of bromodeoxyuridine into DNA by high performance liquid chromatography using a novel fluorescent labelling technique

5'-Bromo-2-deoxyuridine (BUdR) is a halogenated pyrimidine analogue that is an efficient radiosensitizer through its incorporation into DNA in place of thymidine. Radiosensitization is proportional to percentage replacement and we present here a novel derivatization technique that specifically labels the thymidine and BUdR with 4-bromomethyl-7-methoxycoumarin (BrMMC) to give the highly fluorescent coumarin derivatives which are quantitated using high performance liquid chromatography (HPLC). This allows for a simple single-stage DNA hydrolysis and sensitive peak detection. Data are presented showing the incorporation with time of BUdR into the DNA of Chinese hamster V79 cells. Attention is also drawn to the care needed in the selection of enzymes required for DNA digestion.

The clinical utility of magnetic resonance imaging in 3-dimensional treatment planning of brain neoplasms

Results of the clinical experience gained since 1986 in the treatment planning of patients with brain neoplasms through integration of magnetic resonance imaging (MRI) into computerized tomography (CT)-based, three-dimensional treatment planning are presented. Data from MRI can now be fully registered with CT data using appropriate three-dimensional coordinate transformations allowing: (a) display of MRI defined structures on CT images; (b) treatment planning of composite CT-MRI volumes; (c) dose display on either CT or MRI images. Treatment planning with non-coplanar beam arrangements is also facilitated by MRI because of direct acquisition of information in multiple, orthogonal planes. The advantages of this integration of information are especially evident in certain situations, for example, low grade astrocytomas with indistinct CT margins, tumors with margins obscured by bone artifact on CT scan. Target definitions have repeatedly been altered based on MRI detected abnormalities not visualized on CT scans. Regions of gadolinium enhancement on MRI T1-weighted scans can be compared to the contrast-enhancing CT tumor volumes, while abnormalities detected on MRI T2-weighted scans are the counterpart of CT-defined edema. Generally, MRI markedly increased the apparent macroscopic tumor volume from that seen on contrast-CT alone. However, CT tumor information was also necessary as it defined abnormalities not always perceptible with MRI (on average, 19% of composite CT-MRI volume seen on CT only). In all, the integration of MRI data with CT information has been found to be practical, and often necessary, for the three-dimensional treatment of brain neoplasms.

Three-dimensional treatment planning of astrocytomas: a dosimetric study of cerebral irradiation

To demonstrate that 3-dimensional planning is both practical and applicable to the treatment of high-grade astrocytomas, 50 patients over a 2-year period have received cerebral irradiation delivered in focussed, non-axial techniques employing from 2 to 5 beams. Astrocytomas have been planned using rapid, practical incorporation of CT data to define appropriate tumor volumes. Tumor + 3.0 cm and tumor + 1.5 cm volumes have been treated to conventional doses of 4500 cGy and 5940 cGy, respectively, using beam orientations that maximally spared normal remaining parenchyma. Analyses of 3-dimensionally calculated plans have been performed using integral dose-volume histograms (DVH) to help select treatment techniques. Using identical CT-based volumetric data as input for generation of Beam's Eye View (BEV) designed blocks, DVH curves demonstrate dosimetric advantages of non-axial techniques over conventional parallel-opposed orientations. Assessment of the non-axial techniques in selected cases indicates that uniform target volume coverage could be maintained with a typical reduction of 30% in the total amount of brain tissue treated to high dose (95% isodose line).