Radiation Biophysics: Introduction

Lecture notes for Wednesday 22 January 2003
Andy Howard

Greetings!

This course is intended to provide you with an understanding of what happens when ionizing radiation interacts with biological tissue. Many of you are taking this course as a part of the Health Physics curriculum at IIT, within which you have received or will receive substantial information about ionizing radiation: how it is produced, what it is used for, how to deliver it, how to quantitatite it, and how to minimize exposure of people and things to it. You have also gotten some information about the biological effects of radiation from other courses. In this course the emphasis is on the biological effects, both harmful and beneficial, of radiation. But to put those biological issues in context we will spend some time discussing radiation physics and radiation chemistry. I am hoping we won't have to put in a lot of time on those subjects, since most of you will have treated those subjects in other courses.

Who is your instructor?
I am in the biology faculty within the Biological, Chemical, and Physical Sciences Department at IIT. But my graduate degree is in physics, so I'm reasonably familiar with physics and chemistry as well as biology. My graduate work and my professional concentration have been in macromolecular crystallography, which is the study of the three-dimensional structures of large biomolecules by means of X-ray diffraction. So although I am not a health physicist by specialization, I do use ionizing radiation (in the form of X-rays, both from laboratory sources and electron storage rings) in my professional life, and my research is often affected by concerns for the radiation safety of my experiments. In a sense I'm a consumer of knowledge about radiation biophysics. I also did a one-year postdoc (1983-84) at a toxicology laboratory in Albuquerque where much of the research is on the biological effects of ionizing radiation, and some of that understanding has (I hope) rubbed off.

How is this course going to work?
This class will be taught on Wednesday evenings from now through the first week in May, with one week off in March. Currently everyone enrolled is taking it over the internet, although in principle we could end up with one or two students taking it live or by television. I expect the PowerPoint-plus-live-video versions of these lectures to be out on the web within a day or so of each class. The classes will be primarily lectures, but there will be substantial opportunity for discussion. We will start every class except this one by going over the homework assignment. The homework is not actually due until two days after class (technically at 11:59 pm on the Friday evening, nine days after the issuance date), so we won't answer the homework questions in class, but we will discuss how the problems work, and if there are items that require clarification we'll provide them then. Thus if you need clarifications you should ask for them prior to the lecture. There will be two midterms and a final; the detailed schedule is on the web at http://agni.phys.iit.edu/~howard/radbio/. The course textbook is Edward L. Alpen, Radiation Biophysics, 2nd Ed. San Diego: Academic Press, 1998. 520 pp., cloth. ISBN 0-12-053085-6. $69.95. We will be working fairly closely from the textbook except in our discussion of radiation chemistry (chapter 6) and in a catchall lecture at the end of the course on organismal biology and biochemistry, neither of which is covered in much detail in the text. For those discussions we'll suggest some supplementary readings.

A history of radiation biophysics

Alpen provides an entertaining historical perspective on the early days of radiation research. He provides useful summaries of the roles of Roentgen himself and of Becquerel, Rutherford, and Curie in the early, explosive development of our understanding of X-rays. Alpen includes a quote from Thomas Edison's autobiography, in which Edison's invention of the fluoroscope leads to hair loss in one of Edison's assistants. Edison says, "I then concluded it would not do, and that it would not be a very popular kind of light; so I dropped it." It's worth noting that the first medically observable deleterious effect from X-rays were recorded less than six months after Roentgen's discovery of X-rays. So the history of radiation biophysics goes back almost as far as the history of X-rays.

Quantities, Units, and Definitions

The world of radiation research has gone through a major change in the units that it uses to express quantities. As recently as the 1970's when I was learning radiation quantitation, the traditional units for activity, dose, energy imparted, and equivalent dose were still in common use. In this course we will use the more modern units except in dealing with older research papers. Thus the units of interest are:
Quantity Definition SI Unit Definition Old Unit Definition Conversion
Exposure Q/m (none) (none) Roentgen    
Dose ED / m Gray Joule/kg rad 100 erg/g 100 rad = 1 Gy
Energy Imparted ED Joule kg-m2/s2 erg g-cm2/s2 107 erg = 1 J