For this Workshop, the organizers have attempted to invite experts from all known centers which are engaged in neutron beam development for neutron capture therapy. The Workshop was designed around a series of nineteen invited papers which dealt with neutron source design and development and beam characterization and performance. Emphasis was placed on epithermal beams because they offer clinical advantages and are more challenging to implement than thermal beams. Fission reactor sources were the basis for the majority of the papers; however three papers dealt with accelerator neutron sources. An additional three invited papers provided a summary of clinical results of Ncr therapy in Japan between 1968 and 1989 and overviews of clinical considerations for neutron capture therapy and of the status of tumor targeting chemical agents for Ncr. Five contributed poster papers dealing with NCT beam design and performance were also presented. A rapporteurs' paper was prepared after the Workshop to attempt to summarize the major aspects, issues, and conclusions which resulted from this Workshop. Many people contributed to both the smooth functioning of the Workshop and to the preparation of these proceedings. Special thanks are reserved for Ms. Dorothy K.

Neutron capture therapy (NCT) is based on the ability of the non-radioactive isotope boron-10 to capture thermal neutrons with very high probability and immediately to release heavy particles with a path length of one cell diameter, which in principle allows for tumor cell-selective high-LET particle radiotherapy. This book provides a comprehensive summary of the progress made in NCT in recent years. Individual sections cover all important aspects, including neutron sources, boron chemistry, drugs for NCT, dosimetry, and radiation biology. The use of NCT in a variety of malignancies and also some non-malignant diseases is extensively discussed. NCT is clearly shown to be a promising modality at the threshold of wider clinical application. All of the chapters are written by experienced specialists in language that will be readily understood by all participating disciplines.

Despite the many advances made in the diagnosis and therapy of cancer, the mortality rate is still about half that of the incidence rate. However, the odds are not evenly distributed. Prognosis for some cancers is good, but for others, few patients will survive 12 months. This latter group of cancers is characterised by a proclivity to disseminate malignant cells in the host organ. The degree of surgery possible may be limited by the critical nature of the organ, and chemotherapy and radiotherapy are of palliative value only. In some cases systemic metastases occur, but in other cases, failure to achieve local control results in death. First among these cancers are the high grade brain tumours, astrocytoma 3,4 and glioblastoma multiforme. Local control of these tumours should lead to cure. Other cancers melanoma metastatic to the brain, for which a useful palliative therapy is not yet available, and pancreatic cancer for which localised control at an early stage could bring about improved prognosis. Patients with these cancers have little grounds for hope. Our primary objective is to reverse this situation with Neutron Capture Therapy (NCT). The purpose of this fourth symposium is to hasten the day whereby patients with these cancers can reasonably hope for substantial remissions. The first symposium on NCT was held in Boston in 1983, followed by Tokyo in 1985 and Bremen, Germany in 1988.

Binary systems for the treatment of cancer potentially are among the most attractive of the new therapeutic modalities that currently are under investigation. The basicconcept is to selectivelydestroy malignantcells whileconcomitantlysparing normal tissue. Neutron capture therapy (NCT) is the binary system that has been the subject of the Fifth International Symposium on Neutron Capture Therapy, which was held September13-17, 1992, in Columbus, Ohio, undertheauspicesoftheInternational Society for Neutron Capture Therapy. Its objective was to bring together researchers from throughout the world and to provide a forum at which they could present the latest advances in the development of Neutron capture therapy. Neutron capture therapy has largely, but not exclusively, focused on the use of boron-10 as the target nuclide. Boron neutron capture therapy (BNCT) is based on the nuclear reaction that occurs when the stable isotope, boron-10, absorbs low-energy non ionizing thermal neutrons to yield alphaparticles and recoiling lithium-7 nuclei. The size and energy of these high linear energy transfer (LET) particles result in their being confined largely to the cells in which the capture reaction occurs. For BNCT to be successful, a sufficient numberof I~atoms mustbe localized within neoplastic cells, and enough thermal neutrons must be delivered and absorbed by the I~ to produce a lethal 1~(n,QVLi reaction. Two major problems must be surmounted.

There are many human cancers which actively synthesize specific characteristic proteins such as melanomas, thyroid cancer and squamous cell carcinoma. Many cancer researchers have of course tried to utilize this specific activity as a key for the selective treatment of cancers. In the past for example, the molecular hybrid compound of DOPA, a substrate of melanin, and nitrogen mustard N-oxide hydrochloride, a ctyotoxic anti-tumor drug, was synthesized as Melphalan and used to treat malignant melanoma. A major problem arose though in that it was soon found to be highly suppressive toward bone marrow and quite toxic while not being remarkably effective. Thus, malignant melanoma could not be cured by it. Such failure led us to develop a novel bimodal therapeutic system which includes the use of non-toxic potentially cytocidal chemicals which selectively accumulate within the cancer cells and which are converted by a controllable modality into an actively cytocidal element in situ. We can now non-surgically cure malignant melanoma and glioblastoma with our selective cancer treatment, neutron capture therapy (NCT); as can be found in this volume. Included are 124 papers on the latest breaking developments discussed at the Sixth International Symposium on NCT for Cancer held in Kobe during the late autumn of 1994.

Frontiers in Neutron Capture Therapy contains current research results originally presented at the Eighth International Symposium on Neutron Capture Therapy for Cancer in La Jolla, CA. This comprehensive collection of peer-reviewed manuscripts is showcased in two volumes covering all aspects of the development of this multidisciplinary approach to cancer therapy. Volume I of this work includes clinical results and current progress in treatment planning, neutron sources and dosimetry, while Volume II presents the synthesis, pharmacology and tissue-targeting design of boron compounds, including work on preclinical dosimetry and radiobiology. Intended for researchers and clinicians involved with or interested in new modes of cancer therapy, this volume will also serve as a useful guideline for scientists, students, and practitioners in the field.

The European Collaboration on Boron Neutron Capture Therapy (BNCT), conceived in 1987 and successful in 1989 in gaining financial support as a Concerted Action through the Medical and Health Research Programme of the Commission ofthe European Communities (CEC) in Brussels, considered it an opportune moment to hold its annual Plenary Meeting on 18-20 Septem ber 1991 as an International Workshop entitled "Towards Clinical Trials of Glioma with BNCT". The background to this consideration was influenced by the world-wide resurgence ofinterest in NCT over the last 2 decades and by the exemplifica tions at the Fourth International Symposium on Neutron Capture Therapy for Cancer held in Sydney in December 1990, where it was strongly indicated that within the next 2 years clinical trials would be started both in Europe and the United States. In particular at the High Flux Reactor of the Joint Research Centre of the CEC at Petten in The Netherlands, an epithermal neutron beam designed and installed in the summer of 1990 recently became operable at full reactor power. An extensive series ofexperiments, including the nuclear and radiobiological characterisation of the beam and a healthy tissue tolerance study on canines has started and has the aim to define the preconditions for clinical trials onpatients with Grade III/IV glioma. However, as with any other new therapy modality, it must be demon strated that BNCT is safe for the patient and has a reasonable chance of being an effective therapy.