thyroid gland absorbed radiation dose from intra-oral radiographs in children who suffered a dento

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2008
MSc DMFR – Johan K.M. Aps -
THYROID GLAND ABSORBED RADIATION
DOSE FROM INTRA-ORAL RADIOGRAPHS IN
CHILDREN WHO SUFFERED A DENTO-
ALVEOLAR TRAUMA

Author
Johan Karel Maria APS
DDS, MSc Paed. Dent., PhD
Research Assistant Professor Ghent University, Dental School
Senior Consultant Ghent University Hospital, Dental School and Dental out-patient clinic

Year of submission of this thesis : 2008
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THYROID GLAND ABSORBED RADIATION DOSE FROM INTRA-ORAL RADIOGRAPHS IN
CHILDREN WHO SUFFERED A DENTO-ALVEOLAR TRAUMA

“ A project report submitted in partial fulfillment of the Master of Science degree in
Dental and Maxillofacial radiology from the University of London. Unit of Distance Learning,
King’s College London Dental Institute.”

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Dedication
This work is dedicated to my wife, Myriam, and our two daughters, Nathalie and Charlotte,
who have been patiently enough to let me achieve this, while I had a fulltime professional
task at the Ghent University and the Ghent University Hospital and not to forget being a
husband and “dad”. It has not been “easy” for you.
Thank you very much for this opportunity, my dear “girls”.

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Abstract
Children who suffered a dento-alveolar trauma are subjected to an initial radiographic
examination and in most cases follow-up radiographs are necessary. However, the angle of
projection, particularly in children under the age of 10 and under critical conditions,
frequently put the thyroid gland in the path of the X-ray beam.
The first aim of the present study was to evaluate the available literature of 1998 to June
2008 on thyroid gland absorbed dose from intra-oral radiography, with a focus on children.
Secondly, assessment of the number of radiographs per dento-alveolar trauma case in the
Ghent University Dental Outpatient Clinic in children aged 1 till 18 years old. Thirdly, a
retrospective assessment, by means of Personal Computer X-ray Monte Carlo calculations
(PCXMC® version 1.5), of the absorbed radiation dose by the thyroid gland from intra-oral
and occlusal radiographs of the maxillary incisors, based on the projection angles, derived
from the radiographs from the Ghent University Dental Outpatient Clinic.
From the clinical data it was observed that in children younger than 5 years, the occlusal
radiograph was used in 87% of cases. For children older than 5, several projection
techniques were used in equal proportions. Three projection angles, 30°, 45° and 65°
respectively, were further used for PCXMC® calculations. It was found that irrespective of
the exposure settings, the absorbed dose by the thyroid gland decreased with age and that
there were significant differences between ages (1, 5, 10, 15 and 20 year olds). A projection
angle of 45° caused a significantly higher absorbed dose by the thyroid gland than did 30° or
65°. Therefore the routine use of a thyroid radiation protection shield is recommended in
order to reduce the dose to the thyroid gland.
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Furthermore similar calculations were executed by means of the PCXMC® version 2.0 in
which the weighting factor for the salivary glands was included (ICRP 2005 guidelines).
Besides the obvious absorbed dose by the salivary glands, it was observed that the dose
absorbed by the thyroid gland was lower when estimated with PCXMC® version 2.0.
Therefore, prudence should be called when comparing estimated values from different
PCXMC® versions.

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Contents

Chapter 1…………………………………………………Introduction………………………………p 10.
Chapter 2…………………………………………………Aims of the study………………………p 25.
Chapter 3…………………………………………………Material and Methods………………p 27.
Chapter 4…………………………………………………Results of literature search……….p 30.
Chapter 5…………………………………………………Results of clinical data……………….p 44.
Chapter 6…………………………………………………Results of PCXMC calculations…..p 50.
Chapter 7…………………………………………………Discussion………………………………….p 74.
Chapter 8…………………………………………………Conclusion…………………………………p 79.
References ………………………………………………………………………………………………….p 80.
Addendum 1………………………………………………………………………………………………..p 84.

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Acknowledgements
I wish to thank Dr. Suk Ng for her guidance since the first year of the MSc. Her thrive was
contagious and I hope to be as inspiring to my own students and colleagues in the future. I
also wish to thank everyone who was involved in the four years of the MSc for their good
work in teaching.
My appreciation to Dr. Klaus Bacher of the Ghent University, dept. of Medical Radiation
Physics, who was helpful with guiding me into the PCXMC® calculation software.
I also wish to express my gratitude to the staff of the Ghent University Dental School to
provide the financial opportunity to let me follow this interesting MSc course, which will
hopefully lead to the development of a successful medical imaging department at the Ghent
University Dental School and Ghent University Dental Out-Patient Clinic .
I also, of course, wish to thank my colleagues of the Department of Paediatric Dentistry of
the Ghent University Dental School, for adapting their work schemes to my MSc schedule for
the past 4 years. As one of them once said at a time of the department’s internal reflection
moments; “what seems right for the School is maybe not that right for the Department and
vice versa”. I agree, but in this case this statement may be shown wrong, as this thesis will
be useful for the Department and for the School.
I want to express my gratitude to two new friends of mine who provided the perfect
environment to study while I was in London. Thank you David and Chris for all you have done
for me and for having me in your house the past 4 years.
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Last but not least, I have to thank my parents, who always taught me to go beyond my
apparent limits and my wife and children for supporting me in this project of 4 years of
extra studying. Without them, I would never have achieved this. Thank you very much!

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CHAPTER 1 : Introduction
Diagnostic information can be retrieved from the patient through an anamnesis (history and
clinical examination) and medical imaging techniques. In dentistry, the latter is mostly
obtained using ionizing radiation. Non-ionizing radiation, namely, ultrasound imaging for
purely dental purposes (e.g. caries detection) is currently not available, but hopefully will in
the future. Intra-oral, as well as extra-oral radiological techniques, e.g. periapical
radiographs and dental panoramic tomography respectively, are being used frequently in
children, adolescents and adults.
Radiation administration is governed by three principles: the ethical justification of an
examination, the choice of equipment and procedural optimization and the ALARA principle.
This quote is from Regulla and Eder (2005)1 and comprises perfectly how every radiological
examination should be performed.
A study carried out in the UK2 in 2004, concerning the UK population radiation dose due to
medical exposures, showed that only 0.36% came from dental exposures (table 1). This is a
low percentage, however, one should take into account that this is an underestimation, as
retakes are probably not included in these calculations. The latter holds also for the other
medical exposures. Nevertheless, these figures are for the entire population, but it would be
a very interesting investigation, to calculate the dose for children under the age of 15. The
relative contribution of dental radiography in this age group may be substantial, compared
to dental exposures in the entire population. The latter may prove to be important, with
other dental radiographic techniques coming on the scene, such as cone beam CT, which
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