Radiation Physics for Medical Physiscists - E.B. Podgorsak

*Á viÄÄ ÁË ÁÜ Ë ±Ë* `} ÁÅ> ]Ë* ± ±]Ë * ]Ë * ]Ë *

i ÍÁiËÖ ÜiÁÄ Í> ÁiË`iËÄ> ÍjË V

V Ë1 ÜiÁÄ ÍßË i> Í Ë i ÍÁii¬>ÁÍ i ÍË vË i` V> Ë* ßÄ VÄ ¤ÉxåË>Üi ÖiË i`>ÁÍÁi>A ]Ë+ÖiLiVËA Ï Ë¤ {]Ë > >`> i > \Ëi¬ `} ÁÄ> J i`¬ ßı V} ±V>

- : :GG4&& 42*:$;;; @ 04*-2*2-2 C 0- @-422 @ BII(3B>>=A

5>5%,=B5I

,5I,A,()I,B(I)5,=, 6:-2*$:* $:0-2 $-#$0 $:*: $EE 4:/,5A,3=%,A,()I,B(I)5,%, 6:-2*$:* $:0-2 $-#$0 $:*: $EE 4:/

+-; E4:/ -; ;C .$ @@@44 46G:-*+@7 000:-*+@; :$$ :$;$:D$#! E+$@+$: @+$+E+40$ 4::6 :@@4&&@+$ 1 @$:- 0 -;42 $:2$#! ;6$ -&- 00GG@+$+:-*+@; 4&&@: 2;0 @-42! :$6:-2@-2*!!:$C;$ 4&&-00C;@: @-42;! :$ -@ @-42! :4 # ;@-2*! :$6:4#C @-4224221- :4&-0104::-2 2GG4@+$:$E G!! 2#2;@4: *$ -2 # @ 2/;7 C60- @-4224& @+-;-6C 0- @-4224: 6 :@; @+$:$4&&-; 6$:1-@@$# 420GGC2#$:#@+$+6:4D-;-42;;4& @+$ $:1 2 46G:-*+@@ EE4&& $6@$1 $: 3! 53>(! -2 -@;@ C::$2@@D$:;-42! 2#26$:1-;;-422&4::C;$;1C;@; 0E G; $$4 @ -2$# &:411 6:-2*$:77 -40 @-42;; :$$0- 0$0@4 6:4;$ C@-422C2#$:#@+$+ $:1 2 46G:-*+@@ E7

6:-2*$:*-; 6 :@@4&& 6:-2*$:* -$2 $8 C;-2$;;2 $#-

;6:-2*$:420-2$7 41

"" 6:-2*$:, $:0 *0 $:0-2 $-#$0 $:*:BII>:-2@$##-2 $:1 2G

+$+C;$;4&&*$2$: 0$#$; :-6@-D$$2 1$;! :$*-;@$:$# 2 1$;! @: #$1 :/;!;$@ 7 -2 @+-; 6C 0- @-422#4$;;24@@-160G! $D$2 -2 @+$+ ;$2 $$4&& ;6$ -&- ;@ @$1$2@! @+ @@;C + 2 1$;1 :$$$F$16@ &:411@+$+:$0$D 2@@6:4@$ @-D$$0 E; 2# :$*C0 @-42;; 2#2@+$:$&4:$$&:$$ &4::*$2$: 0$C;$7

G6$;$@@-2*2 2#26:4#C @-42 , $:0-2! :4@ *4, , :4#C @-422 1 ! $:0-24D$:: 42 $6@ GG$ @C#-4C 0 1 : @$-2$2

4D$::6:4#C @-42 1 ! $-#$0 $:*

Mariani za razumevanje in pomoˇc

Preface

This book is intended as a textbook for a course in radiation physics in academic medical physics graduate programs. The book may also be of interest to the large number of professionals, not only physicists, who in their daily occupations deal with various aspects of medical physics and have a need to improve their understanding of radiation physics.

Medical physics is a rapidly growing specialty of physics, concerned with the application of physics to medicine mainly, but not exclusively, in the application of ionizing radiation to diagnosis and treatment of human disease. In contrast to other physics specialties, such as nuclear physics, solid-state physics, and high-energy physics, studies of modern medical physics attract a much broader base of professionals including graduate students in medical physics, medical residents and technology students in radiation oncology and diagnostic imaging, students in biomedical engineering, and students in radiation safety and radiation dosimetry educational programs. These professionals have diverse background knowledge of physics and mathematics, but they all have a common desire to improve their knowledge of the physics that underlies the application of ionizing radiation in diagnosis and treatment of disease.

The main target audience for this book is graduate students in medical physics and these students are assumed to possess the necessary background in physics and mathematics to be able to follow and master the complete textbook. Medical residents, technology students and biomedical engineering students, on the other hand, may find certain sections too challenging or esoteric; however, there are many sections in the book that they may find useful and interesting in their studies. Candidates preparing for professional certification exams in any of the medical physics subspecialties should find the material useful and some of the material would also help candidates preparing for certification examinations in medical dosimetry or radiationrelated medical specialties.

Numerous textbooks that cover the various subspecialties of medical physics are available but they generally make a transition from elementary basic physics directly to the intricacies of the given medical physics subspecialty. The intent of this textbook is to provide the missing link between the elementary physics and the physics of the subspecialties.

VIII Preface

The textbook is based on notes that I developed over the past 25 years of teaching radiation physics to M.Sc. and Ph.D. students in medical physics at McGill University. It contains eight chapters, each chapter covering a specific group of subjects related to radiation physics that, in my opinion, form the basic knowledge required from professionals working in contemporary medical physics. Most of the subjects covered in this textbook can be found discussed in greater detail in many other specialized physics texts, such as nuclear physics, quantum mechanics, modern physics, etc.; however, these texts are aimed at students in a specific physics specialty. They provide more in-depth knowledge of the particular specialty but provide no evident link with medical physics. Some of these important specialized texts are listed in the bibliography at the end of this book for the benefit of readers who wish to attain a better insight into the subjects discussed. To recognize the importance of relevant history for understanding of modern physics, Appendix 1 provides short biographies on scientists whose work is discussed in this book.

I am indebted to my colleagues in the Medical Physics Department of the McGill University Health Centre for their encouragement, approval and tolerance of my concentrating on the book during the past year. I am greatly indebted to my colleagues Dr. Fran¸cois DeBlois, Dr. Geo rey Dean, Dr. Slobodan Devic, Michael D.C. Evans, Marina Olivares, William Parker, Horacio Patrocinio, Dr. Jan P. Seuntjens and Dr. Frank Verhaegen who helped me with discussions on specific topics as well as with advice on how to present certain ideas to make the text flow better. I also appreciate constructive comments from Dr. Jos´e M. Fernandez-Varea from the University of Barcelona.

I would also like to thank my colleague Dr. Wamied Abdel-Rahman, not only for helpful discussions of the subject matter, but also for his skillful drawing of the 100 figures presented in the textbook. Secretarial help from Margery Knewstubb and Tatjana Niˇsi´c is also very much appreciated.

Special thanks are due to my former teachers Drs. John R. Cameron and Paul R. Moran from the University of Wisconsin and Drs. Harold E. Johns and John R. Cunningham from the University of Toronto who introduced me to medical physics, a truly rewarding profession that brings together one’s love of physics and compassion for patients.

Finally, I gratefully acknowledge that the completion of this book could not have been accomplished without the support and encouragement of my spouse Mariana. Especially appreciated are her enthusiasm for the project and her tolerance of the seemingly endless hours I spent on the project during the past year.

Medical Physics: A Specialty and Profession

Current Status

Medical physics is a branch of physics concerned with the application of physics to medicine. It deals mainly, but not exclusively, with the use of ionizing radiation in diagnosis and treatment of human disease. In diagnostic procedures relatively low energy x rays (diagnostic radiology) and gamma rays (nuclear medicine) are used; in therapeutic procedures most commonly high energy (megavoltage) x rays and gamma rays or megavoltage electrons are used (radiation therapy or radiation oncology or therapeutic radiology).

Other applications of physics to medicine include the use of nuclear magnetic resonance in diagnosis of disease (magnetic resonance imaging), ultrasound in imaging, bioelectrical investigations of the brain (electroencephalography) and heart (electrocardiography), biomagnetic investigations of the brain (magnetoencephalography), medical uses of infrared radiation (thermography), heat for cancer therapy (hyperthermia), and lasers for surgery (laser surgery).

During the past two decades medical physics has undergone a tremendous evolution, progressing from a branch of science on the fringes of physics into an important mainstream discipline that can now be placed on equal footing with other more traditional branches of physics.

The four important sub-specialties in medical physics are related to:

1.Diagnostic imaging with x rays (diagnostic radiology physics)

2.Diagnostic imaging with radio-nuclides (nuclear medicine physics)

3.Treatment of cancer with ionizing radiation (radiation oncology physics)

4.Study of radiation hazards and radiation protection (health physics)

Brief History

The study and use of ionizing radiation in medicine started with three important discoveries: x rays by Wilhelm Roentgen in 1895, natural radioactivity by Henri Becquerel in 1896, and radium by Pierre and Marie Curie in 1898. Since then, ionizing radiation has played an important role in atomic and nuclear physics, and provided an impetus for development of radiology and radiotherapy as medical specialties and medical physics as a specialty of physics.

XMedical Physics: A Specialty and Profession

The potential benefit of x ray use in medicine for imaging and treatment of cancer was recognized within a few weeks of Roentgen’s discovery of x rays. New medical specialties: radiology and radiotherapy evolved rapidly, both relying heavily on physicists for routine use of radiation as well as for development of new techniques and equipment. However, while radiology and radiotherapy have been recognized as medical professions since the early 1900s, medical physics achieved a professional status only in the second half of the last century.

Initially most technological advances in medical use of ionizing radiation were related to improvements in e cient x-ray beam delivery, development of analog imaging techniques, optimization of image quality with concurrent minimization of delivered dose, and an increase in beam energies for radiotherapy.

During the past two decades, on the other hand, most developments in radiation medicine were related to integration of computers in imaging, development of digital diagnostic imaging techniques, and incorporation of computers into therapeutic dose delivery with high-energy linear accelerators. Radiation dosimetry and treatment planning have also undergone tremendous advances in recent years: from development of new absolute and relative dosimetry techniques to improved theoretical understanding of basic radiation interactions with human tissues, and to introduction of Monte Carlo techniques in dose distribution calculations.

Educational Requirements

Pioneers and early workers in medical physics came from traditional branches of physics such as nuclear physics, high-energy physics, and solid-state physics. By chance they ended up working in nuclear medicine, radiology or radiotherapy, and developed the necessary skills and knowledge through on-the-job training. In addition to clinical work, they also promoted medical physics as a science as well as a profession, and developed graduate medical physics educational programs, first through special medical physics courses o ered as electives in physics departments and later through independent, well-structured medical physics programs that lead directly to graduate degrees in medical physics.

Since medical physicists occupy a responsible position in the medical environment, they are required to have a broad background of education and experience. The requirement for basic education in physics and mathematics is obvious, but the close working relationship of medical physicists with physicians and medical scientists also requires some familiarity with basic medical sciences, such as anatomy, physiology, genetics, and biochemistry.

Today’s sophistication of modern medical physics and the complexity of the technologies applied to diagnosis and treatment of human disease by radiation demand a stringent approach to becoming a member of the medical