Medical use of radiation and particle accelerators

Recently, medical use of radiation has progressed markedly with the application of newly developed techniques and modalities. And the progress of radiation diagnosis too, has felt the impact of imaging techniques since the introduction of X-ray computerized tomography (X-ray CT). In radiation therapy, efforts have been concentrated on studies to improve local control rates of radioresistant cancers and locally advanced cancers, which remained a problem even after the introduction of megavoltage radiation therapy machines. Particle radiation, characterized by an excellent dose distribution as well as the features of high LET radiation, has been introduced in to clinical research for use in radiation therapy. Other studies with particle radiation suggests that the short lived radioisotopes produced by accelerators will open up a new era for nuclear medicine. This paper looks at the present status and some of the future problems in the medical use of radiation and radioisotopes in Japan.

The changing role of radiation oncology in cancer management

Radiation oncologists have contributed greatly to the improved quality of care of the cancer patient; this has been shown repeatedly in various reports. The improvements in quality have been achieved because of a greater understanding of the natural history of cancer and a more critical evaluation of the results of clinical treatment. Increasing numbers of physicians involved in radiation oncology are participating in clinical evaluation and in multimodal programs of treatment. Major areas for future research in radiation oncology have been identified. The radiation oncologist is now a fully integrated member of the multidisciplinary cancer team participating in clinical treatment and in national cooperative clinical trials. The radiation oncologist's active participation in multidisciplinary clinical treatment programs is significantly changing the character of cancer management. Integration of new techniques of treatment, new combined programs, and greater emphasis on the efficacies of single treatment programs offer major opportunities to cure many cancers that were previously considered incurable.

The development of radiation therapy in Singapore--its present status & future prospects

X-rays were introduced into Singapore soon after their discovery but their use in therapy did not take place until 1914. Radiation therapy was widely used only after 1949 when the first deep X-ray machine was installed. Since then the number of patients given this treatment has progressively increased, keeping pace with the rising cancer incidence. In 1981, 2533 cases were referred for treatment, out of which 1889 were given radiation treatment. The value of radiotherapy in malignant disease has been established both as a palliative as well as a radical method of treatment. Through improved techniques, better therapy equipment, and greater understanding of malignant disease, results of radical radiotherapy have shown progressive improvement. Further advances can be expected with newer techniques which have been put to clinical trials recently. These are planning with CT Scan, conformation radiotherapy, radiation sensitizers and protectors, hyperfractionation, hyperthermia, intraoperative radiotherapy, heavy particle radiotherapy and isotopic immunoglobulin therapy.

Radiation therapy, local tumor control, and prognosis in bronchogenic carcinoma: current status and future prospects

While the overall prognosis for cure of bronchogenic carcinoma remains poor for most patients, there is a growing body of evidence suggesting that rationally optimized local therapy may benefit a significant subset of patients. Local therapy in this context includes any systemic therapy (such as chemotherapy or immunotherapy) that enhances local tumor control in the chest. Compared with many other human epithelial cancers, the total local tumor burden is large for many nonresectable lung cancers and not within the tolerance for control by radiation alone. Thus there is growing evidence that combined surgery and radiation treatment will improve results, especially in the differentiated tumors. Proper selection of patients is important and must include histologic stratification in addition to conventional TNM staging. It is projected that much useful research can be conducted during this decade using clinical tools now available and those that are being tested in early clinical trials throughout the world. Likely candidates for such improvements are both oxic and hypoxic radiosensitizing drugs that should decrease the death rate from uncontrolled local cancer in the chest.

Developing aspects of radiation oncology

Both physics and radiobiology provide growing points in modern radiotherapy. Better physical dose distributions appear to be still worth achieving and can be obtained from beams of protons, heavy ions, or negative pi mesons because a peak region of high dose is deposited at depth in tissue. The heavier ion and pions also have biological properties of high LET radiation which could be important: the radioresistance of hypoxic cells in tumors is less, and tissues which are proliferating fast may be relatively more vulnerable. Although fast neutrons provide ordinary physical dose distributions, their high LET properties are similar to those of ions as heavy as neon. Drugs which specifically radiosensitize hypoxic cells offer a way of determining with certainty how important hypoxic cells are in radiotherapy. Hyperthermia is in its early stages but promises to damage just those cells poor in nutrients which are relatively resistant to ionizing radiation. Radioprotecting drugs, which depend upon poor uptake in tumors but high uptake in normal tissues, are also being tested.

The 85th frontier

Eighty-five years ago, radiation therapy was discovered, with the restriction of treatment being skin tolerance. This led to time-dose graphs quantitating cure or necrosis. The advent of supervoltage radiation, with skin sparing, treatment simulation and planning, immobilization devices, focus blocks, and computerized tomographic scans, ushered in the era of precision treatment. Radiobiology introduced the hypoxic core and radiation sensitizers. New data concerning the biologic principles of fractional dose, total dose, homogeneity, low-dose implantation, and integration of radiation with surgery, as well as recent protocols, indicate new opportunities for increased local control, cure, and improvement in quality of life.