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Imaging
Radiation Dose And The Use Of
Bismuth Shielding In Scoliosis
Imaging
Carolyn Heyes
Medical Imaging Department
Royal Children’s Hospital Melbourne
“Research indicates an increased risk of childhood acute
lymphocytic leukaemia in plain film studies and an
increased risk of fatal breast cancer from scoliosis series.
The linear, no-threshold model, which states that no level
of radiation exposure is without consequence, is currently
the best estimate of risk. The younger the patient at the
time of exposure, the greater the risk of developing a fatal
cancer “
Radiology February 2005
U.S. National Cancer Institute
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Retrospective study
5,466 women with scoliosis
Average of 24.7 x-rays prior to 1976
70% higher chance of developing breast cancer
Radiation exposure is proportional to an
increased cancer risk
Full spine dose 1940 to 1959 6-200 times higher
than today
ALARA principle should always be followed
Bismuth
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Heavy Metal
Chemical Symbol Bi
Atomic Number 83
Causes beam hardening and therefore
decreases absorbed radiation dose
Radiolucent
Study Aims
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Multi-stage study commenced in April 2005
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To identify the modality with the lowest recorded skin entry
and exit doses
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To standardise the imaging performed
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Evaluate the effectiveness of bismuth shielding
Breast Shields
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RCH current protocol
does not use breast
shields
Copper shielding used in
chiropractic spine
imagining
Bismuth more flexible and
user friendly
No research available on
bismuth use in general
imaging
Commercially available
bismuth shields
Method
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Method
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85 kg Alderson Rando
Anthropomorphic
phantom
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Tape placed at Thyroid,
Breast and Symphysis
2.4m FFD
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PTW Diados Dosometer
used
Philips MD Eleva Fluoroscopy room on High
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Pilot test showed no
variation in exposures
within each modality
Philips general room with AGFA CR Full Leg/Full
Spine cassette holder with a 1.5m FFD
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Philips Digital Diagnost DR room with a fixed
Quality mode with a fixed 1.25m FFD
Bismuth shielding reduced
doses by:
Method
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5 exposures for each level
z
z
z
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No shielding
Lead shielding
Bismuth shielding
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Shielding placed on
posterior surface
Phantom positioned PA
erect
4ply sheet of bismuth
0.06mm lead equivalent
Skin entrance dose
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Skin exit dose
z
Thyroid 40%
z
Thyroid 15%
z
Breast 50%
z
Breast 30%
z
Gonads 20%
z
Gonads 20%
Skin Entry Dose - Bismuth
Skin Exit Dose - Bismuth
Skin Entry Dose
120
CR
DR
Fluoro
100
M
i
c
r
o
g
r
a
y
80
Skin Exit Dose
M
i
c
r
o
g
r
a
y
60
40
20
20
CR
15
DR
Fluoro
10
5
0
Thryoid
0
Thryoid
Breast
Gonads
Breast
Gonads
Overall Dose - Bismuth
Dose measurements
300
Total D ose
CR Skin Entry
DR Skin Entry
Fluoro Skin Entry
CR Skin Exit
DR Skin Exit
Fluoro Skin Exit
140
120
M
i
100
c
r
200
150
100
50
60
r
a
total skin entry
total skin exit
80
o
g
250
0
40
y
20
CR No Shielding
CR Bismuth
Shielding
DR No Shielding
DR Bismuth
Shielding
Fluoro No
Shielding
Fluoro Bismuth
Shielding
0
Images from each room
DR
Fluoroscopy
Limitations of Study
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Measurements were recorded for a small area
only
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Image quality has not been measured
accurately.
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The phantom is the equivalent of an 85kg adult.
CR
The Future
References
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Orthopaedic surgeons happy with bismuth
shielding
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Discussions with bismuth manufacturers
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Further work with equipment specialists to
optimize image processing
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Further studies on the use of Bismuth shielding
in general examinations
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Doody, Michele Morin, et al. (2005) Breast Cancer Mortality After Diagnostic Radiography:
Findings From the U.S. Scoliosis Cohort Study Spine, Vol 25, No.16.
Kusher, David C, et al. (1986) Radiation Dose reduction in the Evaluation of Scoliosis: An
Application of Digital Radiography Radiology 161:175-181
Geijer, Hakan, et al. (2001) Digital Radiography of Scoliosis with a Scanning Method: Initial
Evaluation Radiology 218:402-410
Fahr, Michael J, et al. (2003) Digital Radiography in the Diagnosis of Toddler’s Fracture
Southern Medical Journal Vol96 No3 234-239
Fricke, Bradley L, et al (2002) In-Plane Bismuth Breast Shields for Pediatric CT: Effects on
Radiation Dose and Image Quality Using Experimental and Clinical Data AJR 180 407-411
Rehani, Madan M, Berry, Manorma (2000) Radiation Doses in Computed Tomography BMJ
320 593-594
Hopper, Kenneth D et al. (2001) Radioprotection to the Eye During CT Scanning AJNR 22
1194-1198
Frush, Donald P et al. (2003) Computed Tomography and radiation Risks: What Pediatric
health care providers Should Know Pediatrics Vol112 951-956
Ullrich, Peter F (2001) Understanding idiopathic scoliosis www.spine-health.com (Updated
March 30, 2004)
Mayo Clinic Scoliosis www.mayoclinic.com
Blackman, Ronald, Smith, Jason Scoliosis Treatment www.scoliosisrx.com (updated October
5th 2005)
Fenner, Louise (1984) Reducing Patient Exposure During Scoliosis Radiography Dept of
health and Human Services (U.S.) publication
The Scoliosis Association of Australia What is Scoliosis? www.scoliosis.org.au
References
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Egan, Ingrid. (1992) Comparison of imaging techniques currently used for limb
measurement. The Radiographer 39, 1 pp4-8.
Horsfield D & Jones SN (1986) Assessment of inequality in length of the lower
limb. Radiography (UK) v52,no605 pp223-227.
Tostevin J.(1992) Leg Length Measurement - A Simple Rule.
The Radiographer vol 39, no.1, pp.9-10.
Willis, Charles E, Slovis, Thomas L. (2005) The ALARA concept in pediatric CR
and DR: Dose reduction in pediatric radiographic exams-a white paper
conference executive summary. Pediatric Radiology 2004 34 Suppl.3ppS162S164.
ICRP web module Radiation and your patient: A guide for medical practitioners.
Neitzel, U. (2004) Pediatric radiation dose management in digital radiography.
MedicaMundi 48/3 pp12-18.
Williams, Peter F. Orthopaedic Management. Blackwell Scientific Publications
1982 pp153-162.
Tachdjian,Mihran O. Pediatric Orthopedics W. B. Saunders Company. Second
edition 1990 pp27-59.