It is now almost three decades since John Lawrence became the first to investigate the biological effects of the then new and strange subatomic particles being produced at the cyclotron in Berkeley, Calif. In the intervening years, these studies have been pursued with vision and imagination by the Berkeley investigators. Elsewhere in this issue of The Journal (p 236), Lawrence, Tobias, and their colleagues present the results of some of their biological experiments. They discuss the role of heavy-particle irradiation in medical research and treatment, and review their own clinical experience with this form of therapy.
Certain features of protons and alpha particles make them especially interesting to the medical investigator and clinician. High-velocity heavy particles do not scatter readily in their passage through matter and produce intense excitation and ionization along their path. They give off energy in small amounts until, as their velocities approach zero, the ionization density