Radiotherapy in Practice - Brachytherapy

234 Pages·2011·2.141 MB·English

by  Hoskin, Peter J., Coyle, Catherine

Foreword
Radiotherapy in Practice - Brachytherapy
(2 ed.)
Edited by Peter Hoskin and Catherine Coyle
Publisher: Oxford University Press Print Publication Date: Jan 2011
Print ISBN-13: 9780199600908 Published online: May 2013
DOI: 10.1093/med/
9780199600908.001.0001
Foreword  
Brachytherapy is one of the earliest forms of radiation delivery and the
first interstitial implant was said to have been performed in Dublin in
1912. By the 1950s the Manchester system, with Paterson and Parker’s
relatively simple rules and tables, allowed brachytherapy to be
disseminated widely and performed safely, throughout the world. In the
1960s radium was gradually replaced by artificial isotopes such as
iridium, plus, the development of after loading, which was often used with
the then new, Paris System of rules and dosimetry. Until the 1980s
trainees in radiation oncology were not only expected to be familiar with
the theory, indications and the dosimetry of brachytherapy, but, also to
have developed competence in practice, by supervised training in the
operating theatre. Over the last few years several factors have arisen
which have significantly changed brachytherapy practice. The application
of computer dosimetry, remote afterloading with dose optimisation and, 3-
D image guided source placement have made the process much safer and
more effective, but also very much more complicated, requiring
considerable multidisciplinary cooperation. Although the indications for
brachytherapy have expanded in some areas, such as prostate cancer,
other previously common indications, such as head and neck cancer and
gynaecological cancer, have reduced substantially, both as a result of
falling incidence and, improvements in surgical techniques, which have
become the treatment of choice for many patients, previously referred for
brachytherapy. This means that, in smaller departments, there are very
Page 1 of 2
Foreword
few cases referred for this increasingly complex and demanding
technique, so that it is extremely difficult to retain and develop expertise.
Many have therefore correctly decided to refer potential cases to larger
regional centres where expertise can be maintained and there are
sufficient cases for teaching and training. As a result, it is quite possible
that some trainees are never exposed to brachytherapy. The risk is not
just that they become unable to perform the technique, but also, that they
become unaware of the indications and unique advantages of this form of
treatment and that many patients who could benefit are denied this
option. This book is therefore essential reading for all radiation
oncologists and their trainees so that they can become familiar with the
theory the indications and the results of brachytherapy, and the new
potential that recent advances have made possible. With this knowledge
they will be better placed to advise patients on optimum management and
if the technique is not available in their own centre be aware of the
nearest centre of expertise to which they can be referred. Hopefully,
there will also be some who will be sufficiently inspired to specialise in
this exciting, effective and satisfying form of treatment themselves.
Dan Ash
Leeds, 2010
[Dan Ash was the founder of the joint Leeds/Mount Vernon course on
which this book is based. Many generations have benefitted from his
wisdom and enthusiasm for brachytherapy disseminated through the
Leeds course which was first held in 1981 and annually thereafter until
its incorporation with a similar course at Mount Vernon into the joint
course under the auspices of the Royal College of Radiologists in 2003]
Page 2 of 2
Contributors
Radiotherapy in Practice - Brachytherapy
(2 ed.)
Edited by Peter Hoskin and Catherine Coyle
Publisher: Oxford University Press Print Publication Date: Jan 2011
Print ISBN-13: 9780199600908 Published online: May 2013
DOI: 10.1093/med/
9780199600908.001.0001
Contributors  
P Bownes
Consultant Physicist, St James Institute of Oncology, Leeds, UK
C Coyle
Consultant in Clinical Oncology, St James Institute of Oncology, Leeds,
UK
P J Hoskin
Consultant Clinical Oncologist, Mount Vernon Hospital, Northwood,
Middlesex, UK and Professor of Oncology, University College
London,London, UK
C Richardson
Principal Physicist, St James Institute of Oncology, Leeds, UK
C D Lee
Consultant Physicist, Clatterbridge Centre for Oncology, Bebington,
Wirral, UK
G Lowe
Senior Physicist, Mount Vernon Hospital, Northwood, Middlesex, UK
A Sun Myint
Consultant Clinical Oncologist, Clatterbridge Centre for Oncology,
Bebington, Wirral, UK
Page 1 of 1
Acknowledgements
Radiotherapy in Practice - Brachytherapy
(2 ed.)
Edited by Peter Hoskin and Catherine Coyle
Publisher: Oxford University Press Print Publication Date: Jan 2011
Print ISBN-13: 9780199600908 Published online: May 2013
DOI: 10.1093/med/
9780199600908.001.0001
Acknowledgements  
We are indebted to the Medical Illustration departments at St James
Institute Hospital Leeds and East and North Herts NHS Trust
Page 1 of 1
Introduction
Radiotherapy in Practice - Brachytherapy
(2 ed.)
Edited by Peter Hoskin and Catherine Coyle
Publisher: Oxford University Press Print Publication Date: Jan 2011
Print ISBN-13: 9780199600908 Published online: May 2013
DOI: 10.1093/med/
9780199600908.001.0001
Introduction  
Chapter: Introduction
Author(s): P J Hoskin and C Coyle
DOI: 10.1093/med/9780199600908.003.0009
Brachytherapy is the delivery of radiation therapy using sealed sources
that are placed as close as possible to the site to be treated. The very
term ‘brachytherapy’ means ‘near treatment’. It is therefore applicable
for the treatment of tumours where a radiation source can be placed
within a body cavity (e.g. the uterus, vagina, oesophagus, or bronchus) or
where the tumour is accessible to needle or catheter sources being
placed within it (e.g. the breast, head and neck, prostate, and skin). In
fact, brachytherapy has potential applications to most tumour sites. It can
be used as primary treatment or in combination with external beam
radiotherapy.
The principal advantages of brachytherapy lie in the physics of the dose
distribution around a radiation source, which results in a high
concentration of dose imme-diately around the source and a rapid fall-off
of dose away from the source with distance according to the inverse
square law. Other advantages include accurate localization of the gross
tumour volume and immobilization of the area to be treated unlike the
situation with external beam treatment when organ movement and set-up
errors are introduced. The major disadvantages of brachytherapy lie in
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Introduction
the need to access the tumour, often with an operative procedure and the
requirement for skilled personnel to undertake the treatments.
In the early days of radiation therapy, brachytherapy using radium
sources was a novel means of delivering a radiation dose to a tumour. The
development of high-energy external beam machines and the recognition
of the problems associated with radiation protection in the use of radium
resulted in a move towards caesium sources and the development of the
concepts of afterloading in brachytherapy. Afterloading refers to the use
of non-radioactive templates, tubes, or needles to define the implant,
which are then later loaded with the active radioisotope. Early systems
used manual loading, typically with iridium wire techniques using
hairpins or loops. In the modern era, remote afterloading machines have
largely replaced the use of manual live sources, with the exception of low
dose rate seed brachytherapy. Early afterloading machines used
predominantly cobalt or caesium sources; these are gradually being
replaced by modern iridium afterloaders delivering either high dose rate
or pulsed-dose rate brachytherapy.
Sources may be regarded as continuous sources, that is with even
distribution of the isotope along their length often encompassed within a
sheath, for example, iridium wire, point sources or seeds and
discontinuous sources, or source trains, which may be uniform or non-
uniform in their dose distribution along their length, such as that found in
remote afterloading caesium machines.
Dose rate is an important consideration in the radiobiology of
brachytherapy. Three dose rate bands are now defined: low dose rate
based on radium (<1 Gy per hour); medium-dose rate, for example,
caesium (>1 to <12 Gy per hour); and high dose rate (>12 Gy per hour).
When changing dose rate for a particular technique, it is important to
remember that increasing dose rate increases biological effect and,
therefore, demands dose reduction. Low- and medium-dose rate systems
are increasingly being replaced by high dose rate systems and pulsed-
dose rate systems, which mimic low dose rate delivery by delivering small
pulses at high dose rate intermittently, usually hourly.
There have been significant developments in external beam radiotherapy
techniques over the last decade with the widespread introduction of
intensity-modulated radiotherapy, image-guided radiotherapy, and
stereotactic techniques. This represents a major challenge to
brachytherapy, which used alone still offers the optimal approach to
conformal radiation therapy delivery. In combination with external beam
radiotherapy, brachytherapy enables dose escalation within an intensity-
modulated radiation therapy volume with superior dose volume
constraints to surrounding organs at risk compared with external beam
techniques. It is therefore essential that expertise in these techniques are
maintained and developed.
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Introduction
The following chapters seek to provide the reader with a sound
infrastructure in the physics and dosimetry of brachytherapy followed by
practical guides on the use of brachytherapy in common disease sites.
While low dose rate, medium-dose rate, and high dose rate techniques
are covered more emphasis is put on high dose rate afterloading
techniques, which are expected to substantially replace the other forms of
brachytherapy over the next decade. The advantage of these machines is
that despite the requirement for fractionated treatments they allow short
radiation exposure times and replace several days of inpatient treatment
with outpatient therapy. The small source size, <2 mm diameter, within
flexible catheters results in a very versatile treatment technique, which
can be delivered to many body sites and the use of varying dwell times
throughout the active length of the applicator means that each treatment
can be individualized to ensure optimal coverage of a defined planning
target volume. The radiobiology of high dose rate introduces the concept
of fractionation into brachytherapy but with increasing use and familiarity
of standard schedules the initial uncertainty that surrounded this
approach is rapidly fading.
The other major development in brachytherapy in recent years is the use
of image guidance. Brachytherapy-treated volumes are no longer defined
by the implant itself but, analogous to external beam planning, a clinical
target volume is defined with the implant in situ and using the flexibility
of the stepping source afterloader, dose delivery is tailored to cover the
volume. A major advantage of brachytherapy, however, is that unlike
external beam there is no requirement to redefine an expanded planning
target volume, as there is no set-up error or organ motion to account for.
Thus, for brachytherapy the clinical target volume is the planning target
volume.
This book has been written to provide a practical guide to the use of
brachytherapy in current practice. The contents are not exhaustive and it
is recognized that there will be many individual variations in practice,
brachytherapy remaining one of the few arts in oncology that allows the
practitioner to optimize treatment through individualization and
experience. For this reason references and suggested further reading is
given at the end of each section for those readers wishing to gain more
detailed background information.
The editors are current practitioners at Mount Vernon Cancer Centre,
Northwood (PJH) and St James Institute for Oncology, Leeds (CC) in the
UK. They organize the annual joint brachytherapy teaching course run
through the Royal College of Radiologists in the UK on which the
contents of this book are based.
Page 3 of 3
Isotopes and delivery systems for brachytherapy
Radiotherapy in Practice - Brachytherapy
(2 ed.)
Edited by Peter Hoskin and Catherine Coyle
Publisher: Oxford University Press Print Publication Date: Jan 2011
Print ISBN-13: 9780199600908 Published online: May 2013
DOI: 10.1093/med/
9780199600908.001.0001
Isotopes and delivery systems for brachytherapy  
Chapter: Isotopes and delivery systems for brachytherapy
Author(s): C Lee and G Lowe
DOI: 10.1093/med/9780199600908.003.0010
2.1 Introduction
The aim of this chapter is to consider which radioactive materials
might be suitable as brachytherapy sources, to describe some practical
brachytherapy sources, and to consider how these sources may be
applied to the patient in a controlled and safe way. It is assumed that the
reader has some familiarity with the basics of radioactivity and the
emissions from radioactive substances.
Radioactive sources for brachytherapy are now available with many
radionuclides and in various shapes and sizes, and there is no such thing
as an 'ideal' brachytherapy source. Different sources have different
applications depending on their emission type and radiation energy and
how they are constructed. However, it is possible to state some basic
requirements:
1. The radionuclide must have a half-life of a few days or more for
permanent implants and preferably at least a few weeks for
temporary implants. Large corrections for radioactive decay during
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Isotopes and delivery systems for brachytherapy
a temporary implant should be minimized. A long half-life for stock
sources will give them a useful working life. Very short half-lives
(e.g. a few hours) are unsuitable.
2. The energy of the emitted radiation should be sufficient to treat
the required application, but not so high that radiation protection
becomes difficult. Charged particle emission should be absent or
effectively screened (except for beta emitters). Most modern
brachytherapy sources emit photons of between about 0.35 and 0.66
MeV, though there are low-energy exceptions to this.
3. The radioactive material should be in a physical form that is
insoluble and non-dispersible and can normally be encapsulated into
a structure to prevent dispersion of radioactive material.
4. The radioactive decay process should have no gaseous or liquid
decay products.
5. The material should be available in a high specific activity.
6. The sources should be available at reasonable cost so that the
treatment does not become financially prohibitive.
Most brachytherapy sources are termed ‘sealed sources’. These are
constructed so that the radioactive material is encapsulated (often doubly
encapsulated) in a container to minimize the risk of loss of radioactive
material. Some sources, for example, iridium wires, are not so
encapsulated but nevertheless the risk of dispersal is very small; these
are termed 'solid sources'. Sealed sources have to be wipe tested for
leakage on a regular basis (1). Preparation equipment for solid sources
has to be checked regularly for contamination.
2.2 Production of radioactive materials
The radioactive materials used in brachytherapy sources are
produced by either neutron activation or are a product of nuclear fission.
In neutron activation, often called the 'n-γ' reaction, a sample of a stable
isotope of the element is placed in a neutron field in a nuclear reactor.
Some of the nuclei of the element capture a neutron and become a
radioactive isotope of the element, with the emission of gamma radiation.
An example is the production of the radioactive iridium-192 from the
stable iridium-191:
With this production method, the product will contain a mixture of the
stable isotope and the radioactive isotope. The activity of the product will
depend on the neutron flux and energy, the probability of nuclei
interacting with the neutrons, the length of time in the reactor, and the
half-life of the product itself.
Some radioactive materials used in brachytherapy are fission products.
The process of nuclear fission arises when large nuclei divide and
produce new elements, which are radioactive. An example is
caesium-137, which arises from the fission of uranium so is a by-product
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Isotopes and delivery systems for brachytherapy
of the fuel rods in a reactor. The desired product has to be separated from
other fission products. A more detailed treatment of production methods
and yield can be found in Aird (2).
2.3 Radionuclides in brachytherapy
This section includes brief descriptions of some of the
radionuclides used for brachytherapy and these are summarized in Table
2.1.
Page 3 of 23