The potential of negative pions for cancer radiation therapy.

Abstract

THE POTENTIAL OF NEGATIVE PIONS FOR CANCER RADIATION THERAPY RICHARD MADEY* There is a major effort under way, not only in the United States but also in Canada and in Switzerland, to exploit a promising approach to cancer radiation therapy. This new approach was made possible through basic scientific research at the frontiers of high-energy-particle physics during the late 1940s and the early 1950s. It involves the irradiation ofa cancerous tumor by a beam ofso-called negative pions. Cancer radiation therapy with negative pions is similar to surgery in the sense that both methods are useful for a circumscribed tumor without metastases. A negative pion is one of the particles of modern physics. It was discovered in 1947 by Lattes, Occhialini, and Powell [I]. Probably the two best-known particles are the electron and the proton. The hydrogen atom—which is the simplest atom—consists of a proton with an electron revolving around it. The proton is nearly 2,000 times heavier than the electron. The pion is heavier than an electron but lighter than a proton. In 1935, the Japanese physicist Yukawa predicted the existence of a particle with a mass intermediate between that of an electron and that of a proton in order to account for the very short range of the strong nuclear force. In 1949, he received the Nobel Prize for this work. Because of its intermediate mass, the particle of Yukawa was called the "meson," which comes from the Greek word meaning "intermediate." Subsequently, when two mesons were discovered, the heavier one was designated by the Greek letter p; the lighter one by the Greek letter µ. Thus, the word "pion" is a convenient contraction for "pi-meson"; similarly , the word "muon" is a contraction for "mu-meson." Both pions and muons were discovered in the cosmic radiation incident on the earth from outer space. The pion was first produced by man at the giant»Present address: Department of Physics, Kent State University, Kent, Ohio 44242. I wish to thank the Lawrence Berkeley Laboratory for furnishing figure 3. I am grateful to Dr. Louis Rosen, director ofthe Los Alamos Meson Physics Facility, for providing me with figures 2, 4, 5, 6, 7, and 8. This work was supported in part by Public Health Service Research Grant CA- 14375 from the National Cancer Institute and by the Northeastern Ohio University College of Medicine. This paper was adapted from a lecture entitled "Physics versus Cancer," which was delivered on November 13, 1973 as the Fall Lecture of the Faculty Lecture Series, College of Arts and Sciences, Kent State University. Perspectives in Biology and Medicine · Autumn 1975 | 7 cyclotron at the University of California at Berkeley [2]. Many experiments were carried out there to study the production and properties of pions and their interactions with matter. Pions with both negative and positive charges were produced. The negative pion carries a negative charge like that of the electron; the positive pion carries a positive charge like that of the proton. A neutral pion—that is, one without any charge—was also found. The negative pion is an unusual particle with unique properties for radiotherapy. Professor Peter Fowler of the University of Bristol gave the 1964 Rutherford Memorial Lecture at the University of Sussex [3]. In this lecture, entitled 'V Mesons versus Cancer?" Fowler made the case for irradiation ofcancerous tumors by negative pions and suggested that negative pion beams be used for cancer radiation therapy instead of high-voltage X-rays or gamma rays from cobalt-60. In 1966 Richman et al. [4] discussed the radiotherapeutic possibilities of negative pions, and in 1972 Raju and Richman [5] wrote a review article on the physical and radiobiological aspects of negative-pion radiotherapy. Role of Radiation Therapy Before exploring the potential of negative pions for cancer radiation therapy, let us take a look at the role of radiation today in the treatment of cancer. Although the causes of cancer are still unknown, treatment with radiation therapy alone or in combination with chemotherapy and surgery helps to save many tens of thousands of lives each year. Surgery aims to remove the cancerous cells, radiation therapy aims to kill them, and chemotherapy...