Neutrons are forever! Historical perspectives

Abstract

Purpose: Neutrons were an active field of radiobiology at the time of publication of the first issues of the International Journal of Radiation Biology in 1959. Three back-to-back papers published by Neary and his colleagues contain key elements of interest at the time. The present article aims to put these papers into context with the discovery of the neutron 27 years previously and then give a feel for how the field has progressed to the present day. It does not intend to provide a comprehensive review of this enormous field, but rather to provide selective summaries of main driving forces and developments.

Conclusions: Neutron radiobiology has continued as a vigorous field of study throughout the past 84 years. Main driving forces have included concern for protection from the harmful effects of neutrons, exploitation and optimization for cancer therapy (fast beam therapy, brachytherapy and boron capture therapy), and scientific curiosity about the mechanisms of radiation action. Effort has fluctuated as the emphasis has shifted from time to time, but all three areas remain active today. Whatever the future holds for the various types of neutron therapy, the health protection aspects will remain with us permanently because of natural environmental exposure to neutrons as well as increased additional exposures from a variety of human activities.

Keywords:

• Neutron radiobiology
• neutron therapy
• boron neutron capture therapy (BNCT)
• neutron brachytherapy
• neutron radiation protection
• neutron health risks
• history of neutron radiobiology

Acknowledgements

Although I never had the pleasure of meeting Gerry Neary, I do wish to record my good fortune at being exposed to his curiosity and analytical scientific approach, and to inheriting his unique custom-designed radiation equipment, after I moved to spend a sabbatical at the Medical Research Council Radiobiology Unit with his colleagues about a year after his death in 1972. DTG.

Disclosure statement

No potential conflict of interest was reported by the author.

Notes

1 The terminology of fast and slow neutrons is explained in a later section.

2 The ICRP (1951) definition of r.b.e. was: ‘The relative biological efficiency of any given radiation has been defined by comparison with the γ radiation from radium filtered by 0.5 mm of platinum. It has been expressed numerically as the inverse of the ratio of the doses of the two radiations (in ergs per gramme of tissue) required to produce the same biological effect under the same conditions.’ At that time, the same term was used for the experimentally measured radiobiological quantity and the weighting factor recommended for use in radiological protection.

3 Obesity was not mentioned in later recommendations of the ICRP!

4 Relative Biological Effectiveness (RBE) was defined as: ‘Biological potency of one radiation as compared with another. It is numerically equal to the inverse of the ratio of absorbed doses of the two radiations required to produce equal biological effect’ (NBS 1957). The reference radiation was usually X- or γ-rays.

5 Depth dose profiles depend also on factors other than the identity (protons or deuterons) and energy of the incident particles, including thickness of the target, size of the collimated field (Goodhead et al. 1977) and the source to skin distance.

Additional information

Notes on contributors

Dudley T. Goodhead

Dudley Goodhead is emeritus director of the Medical Research Council Radiation and Genome Stability Unit at MRC Harwell. His own research interests have been mainly in radiation track structure and the influence of radiation quality on the biological effects of ionizing radiations.