Radiation dose optimisation in biomedical imaging and intervention
International Atomic Energy Agency, Vienna, Austria
Situations in life are never simply black and white. There
are many shades of gray. The gray zones provide a lot of playing ground for
scientists engaged in optimisation. We all understand what is meant by
optimisation, such as �the procedure or procedures used to make a system or
design as effective or as functional as possible� or �making the best of
anything�. Thus, the driving force is getting to the �best�. For example, in
medical imaging, one attempts to choose certain parameters to optimise, such as
image quality and patient dose. Both do not go in the same direction. If one
increases image quality (which is desirable), one ends up increasing patient
dose too (which is not desirable). For radiologists, image quality is the main
focus. How often does one hear a radiologist asking, while reporting an imaging
investigation, �how much radiation dose has been imparted to the patient�?
Similarly, physicists are concerned with radiation dose. It is again not common
to see a physicist asking himself what image quality is associated with the
dose he estimated in an imaging procedure. Optimisation, therefore, tends to
imply the best image quality for a radiologist and the least radiation dose for
a physicist. Neither is desirable without regard for the other. Thus, the dictionary
meaning of �optimisation�, in particular �making the best of anything� is not
meaningful in isolation. The best may be happening in both but what we want to
achieve works in opposite directions for the two parameters. To make things
simpler, it is somewhat similar to the quality of consumer goods that we buy
and the price that we have to pay. Higher quality involves higher price but we
want to create a balance between quality and affordable cost.
In this special thematic issue of Biomedical Imaging and
Intervention Journal (BIIJ), 12 papers contributed by authors from 11 countries
have reviewed the situation in conventional and digital radiography,
fluoroscopy, mammography, PET/CT, computed tomography and radiotherapy.
Educational issues for cardiologist on radiation protection and accident
prevention in radiotherapy, both of which have important role in optimisation,
have also been covered.
A good quality assurance (QA) program should reduce the
need for monitoring. This has been documented by Vano and Fernandez in their
paper on dose management in digital radiography. They present the experience on
an online audit tool for digital radiography that they had developed. Working
on images obtained on many thousands of patients for mammography, chest radiography,
computed radiography and interventional radiology procedures, they show that
very few alarm signals were generated. While continuous monitoring by people is
an undesirable tool in quality management, an automatic online audit system is
Optimisation in general radiography still poses a big
challenge. The variation in doses in large scale surveys are quite high and in
this respect a paper by Colin Martin reviews the methods that can be used for
optimisation. Understanding the role of parameters like kV, filtration,
screen-film combination, anti-scatter grid and automatic exposure control is
crucial. Diagnostic reference levels have proved their value in optimisation
and this has been emphasized.
Computed tomography (CT) has continued to pose challenge
in optimisation. At the rate technology has been progressing during the past 7
years, it has overtaken effective optimisation actions in practice. Virginia
Tsapaki and Madan Rehani in their review cover some aspects of optimisation in
CT indicating the important role users need to play in day-to-day management of
situations in clinical practice.
In view of lack of practical experience in
radiation-induced injuries among medical professionals, diagnosis of such
injuries has often followed a tortuous path. Louis Wagner reviews the
characteristics of radiation-induced injuries to the skin and some actions that
can be taken to reduce their likelihood or severity. Failure of optimisation
can result in injuries. This awareness is important and in that respect an
article by Madan Rehani in this issue presents the role of International Atomic
Energy Agency (IAEA) on interventional cardiologists training in radiation
protection. With interventional cardiologists being intensive user of radiation
and having minimal or no training, this issue attains great importance.
Optimisation in radiotherapy has been dominated by
precision in dose delivery to target tissue as primary goal and reduction of
dose to surrounding normal tissue as a secondary goal. Paul Ravindran in his
review covers optimisation while using imaging tools such as electronic portal
imaging and cone beam CT, which are used prior to delivery of radiation so as
to visualize the organ to be treated. It is now being recognized that repeated
use of the imaging system for 25 to 30 fractions could give considerable dose
to normal tissue and critical organs.
Ola Holmberg in his paper �Accident prevention in
radiotherapy� describes lessons learned from major radiotherapy accidents in
order to highlight patterns seen where accidents have occurred and identify
preventive actions. Although optimisation itself is a tool for accident
prevention, however, the reverse is also true. The lessons from earlier
accidents provide basis for optimisation.
Physicians generally administer similar levels of activity
or activity per unit total body mass to all patients. This has been reasonably
successful in the use of radioiodine against thyroid cancer and hyperthyroidism
wherein the �therapeutic window� (difference in dose levels between what is
experienced by the tumour and that experienced by the most important normal
tissue) is large. Mike Stabin and Glenn Flux discuss the need for
patient-individualised dose calculations to optimise therapy for patients, provide
improved clinical outcome and minimise the risk of unwanted side effects.
Optimisation in the decade-old technology of PET/CT has
many issues pertaining to scanning protocols and artefacts produced by motion.
Habib Zaidi reviews the situation and indicates that differences between PET
and CT breathing protocols might lead to misalignment artefacts owing to
anatomical dislocations of the diaphragm and chest wall during a PET/CT scan.
This requires caution while interpreting a study where patient is suffering
from disease in periphery of the lung. Attention has been drawn to many
technological barriers still existing.
Bertil Axelsson makes a case of comprehensive quality
systems in fluoroscopy to optimise the patient dose and image quality.
|Received 9 June 2007; accepted 11 June 2007
Correspondence: Radiological Protection of Patients Unit, International Atomic Energy Agency, Vienna, Austria. Tel.: +43-1-2600-22733; E-mail: firstname.lastname@example.org (Madan Rehani).
Please cite as: Rehani MM,
Radiation dose optimisation in biomedical imaging and intervention, Biomed Imaging Interv J 2007; 3(2):e50
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