Heavy charged particle irradiation of human cancers.

One of the attractive areas of radiation oncological research is the study of improved local and regional control of resistant tumors through delivery of more effective radiation therapy. A number of potentially useful modalities are under study including combinations of debulking surgery and radiotherapy, chemotherapy and radiotherapy, hypoxic cell sensitizers and radiotherapy, hyperthermia, and multiple daily fractionation of photon irradiation. Radiotherapy with pions, helium and heavier charged particles have several advantageous characteristics for accomplishing this goal. At the University of California Lawrence Berkeley Laboratory (LBL) we have been studying the use of radiotherapy with helium and heavier charged particles which have several advantageous characteristics for delivery of cancerocidal therapy to deep seated tumors. These include greater localization of the radiation dose to the target volume as well as potentially greater tumor cell-killing potency relative to normal cell damage: A significant lessening of the radiation protective effect of hypoxia on tumor cells may be expected when radiation exposures are made with ions heavier than atomic number 10. Heavy ions also depress enzymatic repair mechanisms, decrease variations in radiosensitivity during the cell division cycle, cause greater than expected delay in cell division and decrease the protective effects of neighbouring cells in organized systems. A potential clinical advantage may result from irradiation with heavy ions in the atomic number range of 10-15 if a significant difference in the above parameters can be found between normal tissues and tumors.(ABSTRACT TRUNCATED AT 250 WORDS)