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[en] Radiation therapy remains one of the major forms of cancer treatment. When x rays are used in radiotherapy, there are large variations in radiation sensitivity among tumors because of the possible differences in the presence of hypoxic but viable tumor cells, differences in reoxygenation during treatment, differences in distribution of the tumor cells in their cell cycle, and differences in repair of sublethal damage. When high-LET particles are used, depending upon the LET distribution, these differences are reduced considerably. Because of these differences between x rays and high-LET particle effects, the high-LET particles may be more effective on tumor cells for a given effect on normal cells. Heavy particles have potential application in improving radiotherapy because of improved dose localization and possible advantages of high-LET particles due to their radiobiological characteristics. Protons, because of their defined range, Bragg peak, and small effects of scattering, have good dose localization characteristics. The use of protons in radiotherapy minimizes the morbidity of radiotherapy treatment and is very effective in treating deep tumors located near vital structures. Fast neutrons have no physical advantages over ⁶⁰Co gamma rays but, because of their high-LET component, could be very effective in treating tumors that are resistant to conventional radiations. Negative pions and heavy ions combine some of the advantages of protons and fast neutrons

[en] The potential for chemical modification of radiation injury to normal tissues and to tumors was recognized as the field of radiation chemistry evolved. Chemical modification can be divided into three major areas: radioprotection, chemical sensitization, and cytoxicity. Although modest radioprotection may be obtained by physiologic means, the most important protective agents discovered thus far are the sulfhydryl-containing compounds. Differential radioprotection occurs not only because of decreased protection of hypoxic cells. Chemical sensitizers of radiotherapy fall into two major classes: hypoxic cell sensitizers and halogenated pyrimidines. Because of the high percentage of hypoxic cells in tumors, differential sensitization occurs with chemicals that mimic oxygen. Halogenated pyrimidines are incorporated into the DNA of dividing cells and thus will differentially sensitize tumors located in nondividing normal tissues. Cytotoxic chemicals used in cancer chemotherapy have been selected primarily for antitumor effect. In addition, they may modify the extent of radiation injury. The potential for chemical modification is clear but has only reached clinical significance in randomized trials in combination with cytotoxic chemotherapy. The interim results of ongoing clinical trials with hypoxic cell sensitizers, halogenated pyrimidines, and protectors are presented

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[en] This volume of the Radiation Oncology series features update reports on the current status of primary therapy for lung cancer and the role of radiation therapy in the treatment of hepatomas. Other articles describe the use of stereotaxic interstitial implantation in the treatment of malignant brain tumors and discuss the indications for and results of radiation as the primary or adjuvant treatment of large bowel cancer. Reports on new technological developments examine the biological basis and clinical potential of local-regional hyperthermia and photodynamic therapy. Included are reviews of the role of magnetic resonance imaging in the diagnostic evaluation of cancer and of three-dimensional treatment planning for high energy external beam radiotherapy

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