Principles of Radiation Therapy

Thomas J. Deeley

• Editore: Butterworth-Heinemann
• Anno: 2013
• ISBN:
  9781483280059
• Argomento: Medicina
• Categoria: Medicina interna y diagnóstico

Principles of Radiation Therapy presents the applications, limitations, techniques, and results of treatment and possible complications of radiotherapy. This book discusses the general principles of the treatment. Organized into 15 chapters, this book begins with an overview of the aspects of the study of malignant disease and the experience needed by the radiotherapist to function fully as a clinical oncologist. This text then describes briefly the experiments and discoveries of Marie Curie and Wilhelm Konrad Roentgen. Other chapters consider the fundamental physical principles underlying the use of ionizing radiations. This book discusses as well the aspects of treatment using external beam therapy, the machines used, the method of planning treatment, as well as special features of the treatment. The final chapter deals with the effects of radiation on tumor, the normal cell, the tissue or organ, and on the whole body. This book is a valuable resource for radiotherapists, epidemiologists, pathologists, clinical oncologists, nurses, and medical students.

ONE

Introduction

Publisher Summary

This chapter focuses on the treatment of malignant disease. Benign tumors grow slowly and never metastasize or invade the adjacent tissues but may produce symptoms by their expansion. On the other hand, malignant tumors run a more serious course and will inevitably result in death if not removed or controlled. On the whole, they tend to grow more rapidly than benign tumors, and they may contain numerous mitoses, many of which may be abnormal. Malignant tumors may spread out into the adjacent normal tissues by arm-like processes that grow more rapidly in loose tissues and are held up by more solid tissues such as bone or cartilage. Malignant tumors have the power to disseminate and affect the prognosis. The treatment of malignant disease may be surgery, radiotherapy, chemotherapy or a combination of two or all of these. However, if cure and control are not feasible and if there are no distressing symptoms to palliate, no active treatment is given.

While the general public are normally aware of most hospital specialities, some confusion often exists about the work of the diagnostic radiologist, the radiotherapist and the radiographer. A diagnostic radiologist uses ionizing radiation, usually x-rays, to help in the diagnosis of certain diseases, by providing photographic records of parts of the body or of certain functions carried out by the body; certain contrast media may help to define certain structures and he is an expert in inserting such substances in the most inaccessible parts of the body. A radiotherapist uses ionizing radiation, mainly x-rays and gamma-rays to treat certain diseases, the majority being malignant. He is a clinician responsible for the full care of the patients in his wards or those having treatment in the department. A radiographer can work either in a diagnostic department or a therapeutic department and is responsible for taking films or for giving treatment under medical direction.

The study of radiology is not yet 80 years old and is still in a state of development. At one time it was possible to specialize in both diagnosis and therapy, but the increasing complexities of both branches now make it impossible for one man to have an overall experience of both. In this country the two have been separate for many years and sub-specialities have grown up within each branch-for example, neuroradiology, gastrointestinal diseases, paediatric radiology in diagnosis; therapists may specialize in the treatment of certain tumours, reticuloses, central nervous system, bronchus and so on.

The radiotherapist, according to Professor Franz Buschke of the Tumor Institute, Swedish Hospital, Seattle, Washington, U.S.A., should have a fundamental knowledge in gross and microscopic pathology and of diagnostic techniques for cancer in all locations; judgement as to the indication for and knowledge of the pharmacology and techniques of application of chemotherapeutic agents; a comprehensive understanding of physics, the clinical indication for and the application of techniques of treatment by x-rays, radium and radioactive isotopes plus a knowledge of the general care and psychological management of the patient with malignant disease.

To these requirements must be added a wide knowledge of malignant disease at all sites, its incidence, aetiological factors, symptomatology, methods of diagnosis, other treatment techniques, aftercare and palliation. In recent years we have adopted the term ‘oncology’ to cover the study of all aspects of malignant disease. The radiotherapist must of necessity be an oncologist; in fact, he has practised as such for many years. Oncology is not a medical speciality but a concept; no one person is able to cover with expert knowledge the whole field of this study. He may be concerned with a specific aspect, as an epidemiologist, a surgeon, a pathologist and so on but whatever his particular interests are he will benefit from at least an elementary knowledge or familiarity with the other specialities. A radiotherapist perhaps covers more of the whole oncological concept than any other clinician. He needs to know of the surgical possibilities in a particular disease even though he does not carry out surgical procedures; if the results are better with surgery than with radiotherapy then that is the treatment of choice; if radiotherapy is unsuccessful the possibility of further treatment by surgical or other methods must be considered. The radiotherapist needs to know the pathological characteristics of a tumour because these frequently have bearing on the treatment, the search for possible metastases and the frequency of follow-up examinations. Thus we can go on detailing the experience needed by the radiotherapist so that he can function fully as a clinical oncologist. While consultants in other specialities are concerned with aspects of the study of malignant disease within their speciality few limit their activities to cancer as does the radiotherapist. In addition to his own clinical responsibilities the radiotherapist must seek co-operation with many other workers, in such specialities as surgery, gynaecology, haematology, ear, nose and throat diseases, holding joint consultative clinics whenever possible.

It would be wrong to give the impression that the radiotherapist is a scientist dealing with complex high-powered machines; that he is solely concerned with complicated mathematical calculations of dosimetry requiring a slide rule, calculating machine or computer; or involved in radiobiology so that he can assess the effects of radiation on animal and vegetable organisms. He is not a scientist but a clinician concerned with the treatment aspects of malignant disease in patients and continually striving to improve the results of treatment. In order to do this he extends his work and his investigations outside the mere technicalities of his speciality to encompass a wide knowledge of those aspects of science and medicine which can be applied to the study of malignant disease.

For many years the hope has existed that some day a drug will be developed which will cure all cancers irrespective of site, size, spread, histology–the search is somewhat analogous to that for the philosophers′ stone. It has been said that if such a drug is found there will be no need for the special skill of the radiotherapist, the inference being that radiotherapy is a dying subject not worthy of attracting new trainees. Of course, the same can be said of many other branches of medicine and we have seen the changing pattern that has occurred over the years. Cure or prevention of a particular disease has removed the necessity for further work to control it. Perhaps one day control will come in cancer, in cardiovascular diseases, in chronic renal and hepatic diseases, in arthritic and degenerative diseases and in many of the other diseases which cause severe suffering and death–it is as likely to come in malignant disease as it is in the others. In the meantime it is essential that we do what we can to improve the treatment of the established disease; cancer at present is the second commonest cause of death in Great Britain and in some parts of the country has become the major cause. Its nearest contenders are the cardiovascular diseases, many of which are due to old age and the failure of the body machine to continue because of cardiac or vascular wear; also prominent are accidents due to the improvements in civilization, the use of more complex machinery producing an increased loss of life.

The development of antitubercular drugs has greatly influenced the treatment of tuberculosis. But, tuberculosis is caused by one bacterium –if that organism can be ablated the disease is likely to be fully controlled. Cancer is a much more complex problem: it has many manifestations, we have evidence to make us believe that it is caused by more than one factor, numerous possible causes exist and there is a wide variety of types. We know of some causative agents–for example, tobacco smoking–but no amount of informed publicity has, so far, succeeded in inducing the public to abandon this habit. We know of the threat from certain substances used in industry such as asbestos and nickel, but cessation of production processes in which these are used may seriously disrupt our everyday living. Precautions, therefore, have to be taken to reduce, but not completely eliminate, the risks. Certain diets have been shown to be associated with malignant disease but for certain reasons–economy, the availability of certain foodstuffs or mere individual fancy–it has proved impossible to remove the risk. It may be that in time we may discover an idiosyncrasy–perhaps inherited-which makes an individual develop cancer when exposed to the existing cause. So, much work and study is needed before we have an adequate knowledge of this disease; at the moment we are doing no more than ‘scratch the surface’. In spite of all attempts at prevention the number of new patients with malignant disease increases each year. Cancer is a disease mainly of old age and the removal of many other causes of death has resulted in an ageing population; we can, therefore, expect to see more cases of cancer developing in older people who are less able to withstand radical surgical operations. The proportion of patients referred initially for radiotherapy depends on the locality, the availability of radiotherapy consultation and treatment, the bias of the clinician who first sees the patient and the individual opinion of the radiotherapist. In Great Britain between 50 and 75 per cent of treated patients have radiotherapy as the first method of treatment. There is thus a need for this service to be developed further and for young enthusiastic trainees to be encouraged.

There is unfortunately insufficient recruitment of young doctors to the speciality. This may be due to several factors: the unattractiveness of a speciality that deals with a large proportion of elderly patients with advanced disease for whom little can be done; the belief that nothing can be done for malignant disease, a pessimistic view held by many members of the medical profession as well as by lay people; lack of adequate instruction on the subject at the undergraduate level–radiotherapy is considered to be a subject for postgraduate training and few medical schools take more than a cursory glance at it; the necessity for the radiotherapist in training to acquire a knowledge of physics and of certain other sciences including mathematics and statistics, for which most doctors have little enthusiasm. There are other possible causes which account for the relatively poor attraction to the speciality and they may be similar to those resulting in poor recruitment to other branches of medicine. Such problems need active investigation if staff requirements for the future are to be met.

The radiotherapist’s reward comes when he sees a patient who has been cured and who has returned to normal life, working and enjoying himself and taking an active part in the life of the community. The more hopeless the original condition the greater the pride in achieving a cure. The relief of distressing symptoms, maintenance of human dignity or peace at the time of death, can all be achieved by judicious radiotherapy and this, of course, is good medical practice.

TWO

Discoveries

Publisher Summary

This chapter discusses radium and its usage in radiotherapy for the treatment of tumors. Radium is used to give radiation within the tumor volume. It gives out radiation all the time and, therefore, must be carefully stored away when not in use in the patient. Radium breaks down or decays into other substances—radon, radium A, radium B, radium C, and so on—and eventually ends up as stable lead, which is the decay chain of uranium. Many of the radium techniques that were in everyday use some 15–20 years ago have now been replaced by treatment with megavoltage radiation. However, radium implants are still used in many radiotherapy departments albeit fairly infrequently and depending somewhat on the individual preferences of the radiotherapists. Radium needles are implanted directly into the tumor-bearing tissues. Radium sources may be placed in special applicators and inserted into various parts of the body. In surface therapy, a mould is made to fit the surface of the body, and radium tubes are securely fitted into the mould.

The genesis of radiotherapy can be traced back to November 1895 when Wilhelm Konrad Roentgen first discovered his ‘new kind of rays’. But even before this time the foundations had been laid by the late nineteenth-century scientists who already had considerable knowledge about electricity, magnetism and of the effects of electrical discharges in gases at low pressures. They had been experimenting on these lines for some years and it was quite possible that x-rays had already been produced by scientists without being recognized. This chapter will briefly describe these experiments and the two momentous discoveries of Roentgen and Marie Curie.

THE BACKGROUND

The study of radiation involves knowledge of certain aspects of science, chemistry and physics including the atomic theory, electricity, fluorescence, magnetism, vacuums, photography and so on. Each itself a separate study, together they set the stage for the discovery of x-rays and for the development of the study of radiation.

It is somewhat suprising to find that Democritus (460 B.C.) conceived the idea that all materials were composed of small units called atoms (from the Greek atomos meaning indivisible). He further considered that these atoms varied in size, shape and arrangement and were in motion within the structure which they formed. No further developments occurred in this conception of the atomic theory until the beginning of the nineteenth century when the scientists of that day including Dalton (1766-1844) and Berzelius (1779-1848) founded the concepts of modern chemistry.

In the medieval period there was great interest in the study of alchemy–the translation of base metals into the precious metals gold and silver. We now realize how futile these experiments were, the atomic structure of such metals as lead, iron and copper being entirely different from that of gold and silver. Although we may now look back with amusement on these ambitious experiments, medieval scientists accumulated an astonishing amount of miscellaneous chemical information. We shall see later how important the phenomenon of fluorescence was in Roentgen’s discovery. This phenomenon had been described as early as the late sixteenth and early seventeenth centuries and for many years scientists, including Sir Isaac Newton, were fascinated by this effect. By the end of the nineteenth century the mysteries of fluorescence had to a great degree been investigated as a tool for studying light and other energy sources. Throughout the nineteenth century the study of chemistry developed rapidly and towards the end of that century had become an organized scientific speciality resulting in the isolation of many new substances and elements.

Thus, chemistry was becoming an established scientific study. Let us now investigate electricity. Again we are surprised to find that static electricity was recognized as early as 600 B.C. Friction of such materials as amber and fur was reported by the ancient Greeks but remained nothing more than a peculiar physical phenomenon. Magnetism, too, had been recognized at quite an early stage and compasses were in use in both Europe and China in the thirteenth century. Sir Isaac Newton (1643-1727) built static generators and Robert Boyle (1627-1691) carried out elementary experiments on electricity. Benjamin Franklin (1707-1790) conducted many early experiments on electricity and was able to demonstrate two types of static electricity–positive and negative. In the early eighteenth century an apparatus capable of collecting and storing static electricity was invented–this was called the Leyden jar because it was developed in Leyden, Germany. Even at this early time the possibility of using static electricity in medicine was suggested, but it was many years before electric shock therapy was applied to the treatment of psychiatric patients. Volta (1745-1827) made his outstanding discovery that electricity could be produced by placing two different conducting materials in close apposition; this of course was the first battery and from his name we get the word ‘volt’. Michael Faraday (1791-1867) made important discoveries about electromagnetic induction and these discoveries led to the development of generators, motors and transformers which permitted higher voltages to be obtained. Higher voltages were obtained with the Wimshurst machine in 1860. Towards the end of the century scientists all over the world were carrying out experiments involving electricity using higher and higher voltages.

We must now turn to another advance in science–the development of the vacuum. Early man was for many years worried about the possibility of nothingness and it was Spinoza (1632-1677) who produced the maxim ‘nature abhors a vacuum’. The Italian mathematician Torricelli (1608-1647) invented the barometer and pointed out that the atmosphere could support a certain weight of mercury in the closed glass tube. The space between the top of the mercury and the glass was empty and was a vacuum. This discovery induced men to look for ways of producing a vacuum artificially and air pumps which could exhaust a large part of the air in a tightly sealed vessel were developed in the middle of the seventeenth century. This naturally started off research into ways of improving the vacuum. It was these experiments that produced the tubes which led other scientists to expl...