Third Edition
Edited by
PAM CHERRY MSC TDCR
Senior Lecturer, School of Health Sciences, Division of Midwifery & Radiography, City, University of London, London, UK
ANGELA M. DUXBURY MSC FCR TDCR
Emeritus Professor of Therapeutic Radiography, Sheffield Hallam University, Sheffield, UK
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Library of Congress Cataloging‐in‐Publication Data
Names: Cherry, Pam, editor. | Duxbury, Angela, editor.
Title: Practical radiotherapy : physics and equipment / edited by Pam Cherry, Professor Angela M. Duxbury.
Description: 3rd edition. | Hoboken, NJ : Wiley‐Blackwell, 2020. | Includes bibliographical references and index.
Identifiers: LCCN 2019024040 | ISBN 9781119512622 (paperback) | ISBN 9781119512721 (adobe pdf) | ISBN 9781119512745 (epub)
Subjects: | MESH: Radiotherapy–methods | Radiotherapy–instrumentation | Health Physics | Radiation, Ionizing
Classification: LCC RM849 | NLM WN 250 | DDC 615.8/42–dc23
LC record available at https://lccn.loc.gov/2019024040
Cover Design: Wiley
Cover Image: © Mark_Kostich/Shutterstock
Pete Bridge PhD MSc BSc Hons BSc SFHEA
Senior Lecturer in Radiotherapy, School of Health Sciences, Liverpool University, Liverpool, England, UK
Gemma Burke MSc PgC, BSc Hons FHEA
Senior Lecturer, Faculty of Health and Wellbeing, Sheffield Hallam University, Sheffield, England, UK
Fiona Chamberlain MA MIPEM RSci PgCert (HE) FHEA
Senior Lecturer, Faculty of Health and Social Care, University of West of England, Bristol, England, UK
Jan Chianese MSc TDCR
Head of Radiotherapy, Faculty of Health and Social Care, University of West of England, Bristol, England, UK
Erica Chivers MA MSc HDCR(T) CertISM PgCert
Lecturer in Radiotherapy, School of Health Care Sciences, Cardiff University, Cardiff, Wales, UK
Katheryn Churcher MSc BSc
Advanced Radiation Therapist, Adem Crosby Centre, Sunshine Coast University Hospital, Birtinya, Australia
Kathryn Cooke MSc DCR(T)
Former Senior Lecturer in Radiotherapy, Faculty of Health and Wellbeing, Sheffield Hallam University, Sheffield, England, UK
Angela M. Duxbury FCR MSc TDCR
Emeritus Professor of Therapeutic Radiography, Faculty of Health and Wellbeing, Sheffield Hallam University, Sheffield, England, UK
David Flinton EdD MSc BSc Hons DCR(T) SFHEA
Associate Dean Education (Quality and Student Experience), School of Health Sciences, City, University of London, London, England, UK
Terri Gilleece MSc DCR(T) PgD(NucMed) PgCHEP FHEA
Lecturer in Radiotherapy, School of Health Sciences, Ulster University, Belfast, Northern Ireland, UK
Gareth Hill MSc BSc Hons FHEA
Head of Therapeutic Radiography, Radiotherapy Department, Ninewells Hospital, NHS Tayside, Dundee, Scotland, UK
Cath Holborn MSc PgCert BSc Hons
Senior Lecturer, Faculty of Health and Wellbeing, Sheffield Hallam University, Sheffield, England, UK
Anne J. Jessop MSc BA Hons DCR(T)
Former Senior Lecturer, Faculty of Health and Wellbeing, Sheffield Hallam University, Sheffield, England, UK
Jonathan McConnell FCR PhD MSc PgCLTHE PgCRII BSc DCR (R) CoR Accred
Consultant Reporting Radiographer, Queen Elizabeth University Hospital, Glasgow, Scotland, UK
Dora Meikle MSc BSc
Former Lecturer in Therapeutic Radiography, Queen Margaret University, Edinburgh, Scotland, UK
Ros Perry PDip BSc
Professional Lead Radiotherapy Treatment, Radiotherapy Centre, Ipswich Hospital, Ipswich, England, UK
Paul Shepherd OBE MSc DCR(T)
Head of Radiotherapy, School of Health Sciences, Ulster University, Belfast, Northern Ireland, UK
Renee Steel PGDip, BHSc(RT)
Radiotherapy Quality Manager, Cancer Centre, Guy’s and St Thomas’ NHS Foundation Trust, London, England, UK
Helen P. White Med PgDip(ClinOnc) BSc Hons FHEA
Head of Department –Radiography (Therapeutic, Diagnostic and Ultrasound), Division of Radiography, Birmingham City University, Birmingham, England, UK
Nick White MSc BSc Hons BSc Hons BA SFHEA
Senior Lecturer in Radiotherapy, Department of Radiography, Birmingham City University, Birmingham, England, UK
Caroline Wright PhD MSc PGCE BSc (Hons) DCR(T)
Associate Professor‐Radiation Therapy, Department of Medical Imaging and Radiation Sciences, Monash University, Melbourne, Australia
The field of radiotherapy is a very rapidly changing and developing one. When I first started in the field in the early 1980s I was counseled on more than one occasion to the effect that radiotherapy was a dying trade and I would be best advised to find a different specialism within medical physics. In practice the opposite has proved to be the case. The last few decades have seen incredible developments in treatment delivery and imaging and the process shows no sign of running out of steam anytime soon. Online image‐guided radiotherapy with IMRT (intensity‐modulated radiotherapy) or VMAT (volumetric arc radiotherapy) is now in routine clinical use in every department; a situation which would have been unthinkable only 10 years ago. There are also some very exciting developments just over the horizon including the MR (magnetic resonance)‐LinAc and proton beam therapy.
With this background a new edition of this book is very timely and the editors and authors have taken the opportunity to bring the text right up to date. The new edition builds upon its predecessors with the first eight chapters providing an introduction to the basic scientific principles of radiotherapy. These are followed by chapters on modern treatment planning, image‐guided radiotherapy, and verification. There are also chapters on the role of quality management in radiotherapy and the principles of radiation protection. The final two chapters cover the fields of molecular radiotherapy and brachytherapy.
As with the previous editions the book is primarily intended as a comprehensive resource for student therapy radiographers but it will serve as a very useful introductory text for medical physicists, oncologists, nurses, and other radiotherapy professionals.
The primary aim of the first edition of this book in 1998 was to produce a much needed ‘reader friendly’ up‐to‐date text on all aspects of radiotherapy physics and equipment, as many find this a challenging subject. This theme continued into the second edition, published in 2009. Radiotherapy is a fast‐changing, dynamic profession driven by continual advances in technology and so in the last 10 years much has changed. We have sought feedback from academic and clinical staff as well as students, and in keeping with the previous editions, each chapter in this book has been updated and written by contributors in both academic and specialist clinical fields.
As with the previous editions, this book is written primarily for the undergraduate therapeutic radiographer but it is hoped that it will be a useful reference book for medical physicists, nurses, and clinical oncologists alike. Whilst comprehensive in its own right, the book is also intended to complement other texts currently on the market in order to provide a complete and up‐to‐date understanding of radiotherapy physics and equipment.
The editors and authors of chapters would like to recognize the following authors who have contributed to chapter content that has been published in the previous edition.
Dr Christopher M. Bragg, Dr John Conway, Dr Elaine Ryan, David Duncan, Dr Tony Flynn, Elizabeth Miles, Alan Needham, and Dr Bruce Thomadsen.
Angela M. Duxbury and Anne J. Jessop
The aim of this chapter is to provide a brief introduction and overview of the principles of current radiotherapy practice and to act as a guide for the other chapters presented in this text.
Venturing into the field of radiotherapy physics is one of the most interesting and exciting aspects of radiotherapy practice. The rapid developments in computer and technological innovation continue to impact on changing and advancing practice.
Radiotherapy is a speciality that uses high‐energy ionising radiations to treat cancer and some benign conditions. In 2015, there were 359 960 new cases and 163 444 deaths recorded from cancer in the UK. Over 50% of cancer patients survive for 10 years or more and 27% of cancer patients will receive radiotherapy [1].
The intention of radiotherapy can be curative, known as radical treatment, or it can be given to reduce the symptoms of cancer, known as palliative treatment. It can be used as a treatment modality on its own and/or combined with cytotoxic (cell toxic) chemotherapy and/or surgery.
Radiotherapy delivered from outside the body is known as external beam radiotherapy, using X‐rays (photons) or electrons from a linear accelerator machine or protons produced by a cyclotron (see Chapter 8). It can also be delivered from within the body as internal radiotherapy, by placing sealed radioactive sources directly into tissue or cavities, known as brachytherapy (see Chapter 14), or by administering a fluid/capsule of radioactive material, an unsealed radionuclide, into the body (see Chapter 13).
Once a patient has been referred for radiotherapy, the aim of the treatment process is to undertake detailed imaging to visualise the tumour (see Chapter 6) followed by complex treatment planning (see Chapter 9) to ensure that accurate treatment delivery is achieved (see Chapters 7 and 10) in order to deliver a radiation dose that can destroy the tumour whilst minimising the dose to the surrounding healthy organs.
Radiation absorbed dose (see Chapter 4) is measured in Grays (Gy) and the therapeutic radiation dose administered varies depending upon: the curative intent of therapy; the radio sensitivity of the tumour; the volume of tissue to be treated; and the site of the tumour. To enhance the effectiveness of treatment and to allow normal tissue time to recover from the radiation injury, treatment is given in fractions over a specific period of time, for example, 45 Gy in 15 fractions over 21 days.
A combination of skill, accuracy, and complex technology are dedicated to delivering safe and effective radiotherapy in order to achieve the two competing goals – high tumour control and few treatment complications. Treatment failure to meet the treatment intent can result in the patient's clinical outcome being seriously affected in both the short and the long term. Many things can go wrong in this multi‐step/person/department process and error prevention and quality management (see Chapter 11) is essential to minimise catastrophic consequences for the patient [2].
The nature of ionising radiations means that they cannot be detected by the human senses therefore, in order to be able to detect and accurately measure the amount of radiation being delivered several different methods of radiation detection and measurements have been developed (see Chapter 4).
Working with ionising radiations is safe providing a raft of measures are adopted and followed. Safe working practices are a legal requirement and follow the Ionising Radiation Legislation, the Ionising Radiation (Medical Exposure) Regulations (IR[ME]R) 2017 (IR[ME]R NI 2018) [3] (see Chapter 12).
There are several interaction processes that occur when ionising radiation interacts with matter. These depend on the nature and energy of the primary radiation beam and the structure of the medium through which the radiation beam passes. For X‐ray energies utilised in radiotherapy, these interaction processes are described in Chapter 5.
High‐energy radiation used for radiotherapy treatment can be lethal to both normal and abnormal tissue; this is due to either direct or indirect actions occurring when the radiation is delivered to the target volume within the patient.
Direct action occurs when the cells within the normal tissue or tumour are in the mitosis phase of the cell cycle and the DNA strands are exposed as part of the cell division. The X‐rays strike the DNA chain and cause either a single or double strand break; the result of a double strand break is cell death, however there is a possibility that following a single strand break cells can go on to have further cell divisions.
Indirect action occurs when the radiation ionises the water molecules within the cells and is not directly linked with the cell cycle. When the water molecule is ionised this leaves a H2 element and an O element to restabilise and both these ions seek a partner to join with; some will become a water molecule again (H2O) with no resultant effect. Other ions will combine as H2O2 (hydrogen peroxide), which is toxic to the cells’ internal environment, with the resultant effect that cell death will occur.
Both of these actions are based on the probability that radiation will come into contact with either the cell during mitosis, or water molecules along their path through the patient. As the radiation cannot discriminate between normal and tumour cells there is the likelihood that normal tissue will be affected, along with the tumour, as it is impossible to clearly define the tumour boundary. As a result of any tissue damage, cells in the vicinity will be stimulated to move into the mitosis phase of the cell cycle to repair the damage; this is true for both normal and tumour cells. With all of the tumour cells being included within the treatment volume during a course of radical treatment, the aim is to deliver a tumouricidal dose of radiation to the tumour whilst sparing as much normal tissue as possible; this is known as tumour control probability (TCP) and normal tissue complication probability (NTCP).
Most commonly used radiotherapy beams are electronically produced using a linear accelerator; a machine consisting of a discrete number of components that function together to accelerate electrons before they strike the target to then produce high‐energy photons (X‐rays). These X‐rays are then directed towards the patient and subsequently the tumour through a series of collimation systems. Electron beams are produced using the same principles of accelerating electrons, however the target is removed from the exit window and the electron beam is then used to treat the patient (see Chapter 8).
Proton beams are produced using either a cyclotron or a synchrotron to accelerate the particles by magnetically pulling them through a circular path until the protons reach their maximum speed. The advantage of using a proton beam is that the Bragg Peak depth can be manipulated to more closely match the tumour shape by modulating the beam as it emerges from the head of the machine (see Chapter 8).
Kilovoltage machines were historically the main provider of external beam radiotherapy, until the introduction of Cobalt‐60 units, and subsequently linear accelerators; both of which have the capability to improve the delivery of dose at depth. However, kilovoltage machines (see Chapter 8) still have an important role within radiotherapy when treating superficial tumours, especially smaller lesions or lesions close to the eye.
Radiotherapy can be delivered in different ways using a linear accelerator to deliver high energy X‐rays (photons) or electrons; the majority of patients prescribed radiotherapy will receive their treatment by external photon beams. Treatment can be given with a curative intent, known as radical treatment, or to relieve symptoms, known as palliative treatment.
When delivering radical treatment the radiation dose is higher than for palliative treatment, for example, 60 Gy, and may be delivered using multiple static fields or more commonly by single or multiple radiation beams that sweep in uninterrupted arc(s) around the patient, called volumetric arc therapy (VMAT) incorporating intensity‐modulated beams known as intensity‐modulated radiotherapy (IMRT) designed to deliver a lethal dose across the tumour or tumour site, whilst sparing the surrounding normal tissue (see Chapter 9). Radiotherapy delivered using a linear accelerator for palliative treatments can be given by using a single field or parallel opposed fields, although IMRT/VMAT are increasingly being used for palliative treatments due to the reduced side effects of treatment. Palliative treatment usually delivers a lower dose of radiation, for example, 30 Gy.
In using IMRT/VMAT delivery the treatment planner has the ability to sculpt the doses to the shape of the target thereby optimising the radiation delivery to irregular shaped volumes. It is possible to produce concave distributions of dose in radiation treatment volumes. IMRT/VMAT has the advantage of (i) greater sparing of normal structures like salivary glands, mandible, pharyngeal constrictors, oesophagus, optic nerves, brain stem, and spinal cord; (ii) delivery of a simultaneous integrated boost; and (iii) eliminating the need for multiple field matching. VMAT is an advanced form of IMRT which delivers IMRT‐like distributions in a single rotation of the gantry, varying the gantry speed and dose rate during delivery, in contrast to standard IMRT, which uses fixed gantry position with either step and shoot or dynamic multileaf collimator shaping of the beam (see Chapters 8 and 9). Planning studies using VMAT as the mode of delivering radiotherapy demonstrate shorter planning and treatment times, fewer monitor units for treatment delivery, better dose homogeneity, and normal tissue sparing.
The first step in the radiotherapy treatment process is the accurate localisation of the tumour in reference to external landmarks. Firstly the patient must be CT (computed tomography) scanned (see Chapter 6) in the position in which they are going to be treated, for example supine with their arms elevated to remove them out of the treatment fields. The patient must be immobilised with the aim to ensure the patient is in the same position for each treatment fraction (see Chapters 7 and 10). This is required in order to deliver the planned radiation doses accurately.
Typically, a patient is CT scanned one to two weeks before they start radiotherapy and multiple tattoos may be applied to the patient's skin so that the patient's external anatomy can be aligned accurately with the treatment plan when they come back for their radiotherapy treatment. If external tattoos are to be solely relied upon for accuracy we must assume that the patient's external anatomy is constant and that the target inside the patient remains in the same position every day in relation to the external anatomy.
The patient's CT images are then loaded into a treatment planning system (TPS) which has software that is specially designed to model the energy absorption of multiple beams traversing through the body. The treatment planner selects the target volumes to be treated and the volumes or organs that are to receive as low a dose as possible (known as organs at risk) and the TPS calculates and produces a map of dose distributions, known as a treatment plan. This plan is used as a reference plan to ensure accurate and safe treatment is delivered for each treatment (see Chapter 9).
Image‐guided radiotherapy (IGRT) is any imaging at the pretreatment and treatment delivery stage that leads to an action that can improve or verify the accuracy of the radiotherapy treatment (see Chapter 7). IGRT encompasses a wide range of techniques ranging from simple visual field alignment cheques, through to the more complex volumetric imaging that allows direct visualisation of the radiotherapy target volume and surrounding anatomy. The complexity of the imaging required depends on the anatomical site to be treated (see Chapters 6 and 7).
Techniques can be adopted that will assist accurate dose delivery, for example, Deep Inspiration Breath Hold (DIBH) can be used for patients with left‐sided breast tumours. This can decrease the radiation dose delivered to the heart and can lower the incidence of ischaemic heart disease. This technique involves the patient inspiring to a specified threshold and then holding that level of inspiration during every radiation therapy field delivered (see Chapter 10).
Recent technological advances allow for radiotherapy to be delivered in different modalities, such as intraoperative radiotherapy (IORT) during surgical procedures (see Chapter 8). IORT is defined as the application of therapeutic levels of radiation to a target area, such as a tumour, whilst the area is exposed during surgery. The treatment can be applied using low‐energy (kV) X‐rays, or with electrons. These techniques are most commonly used in the treatment of breast cancer, but can be used for other tumours, e.g. cancer of the cervix.
Proton therapy is a well‐established, effective form of radiation treatment that uses a high‐energy beam of protons rather than high‐energy X‐rays to deliver a dose of radiotherapy for patients with cancer. It works best on some very rare cancers including tumours affecting the base of skull or the spine. Proton beam treatment can be a more effective form of therapy because it directs the all‐important radiation treatment to precisely where it is needed with minimal damage to surrounding tissue. The treatment is therefore particularly suitable for treating childhood cancers.
Stereotactic body radiotherapy (SBRT) or stereotactic ablative radiotherapy (SABR) is a way of giving relatively high doses of radiotherapy to a very small tumour. SBRT is delivered using a linear accelerator and delivers radiotherapy from many different positions around the body; the beams are designed to meet at the tumour. The tumour receives a high dose of radiation and the tissues surrounding it receive a relatively lower dose. This lowers the risk of side effects and increases the TCP.
The underpinning physics principles, details of the equipment, and all aspects of practice that embrace safe and effective radiotherapy treatment are detailed throughout the chapters in this book.