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 ions 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.