Transcript Kalpana M. Kanal, PhD, Puneet Bhargava, MB

Physics Case of the Day
Category CT
Authors: Kalpana M. Kanal, PhD, Puneet Bhargava, MB BS, DNB*,
Brent K. Stewart, PhD
University of Washington Medical Center, *Seattle Childrens Hospital, Seattle, WA
History:
A CT pulmonary angiogram image
(shown) was performed on a 24 year
old female patient with pleuritic chest
pain and increased d-dimers. No filling
defect was identified in the pulmonary
arteries to suggest pulmonary
embolism.
Challenge:
Identify the structure indicated by
arrow and why it is being used for this
exam?
Physics Case of the Day
Category CT
Authors: Kalpana M. Kanal, PhD, Puneet Bhargava, MB BS, DNB*,
Brent K. Stewart, PhD
University of Washington Medical Center, *Seattle Childrens Hospital, Seattle, WA
Answer:
The structure identified by the arrow is
an image of a bismuth shield used
during the clinical exam. Its purpose is
to reduce the dose to the breast of the
24-year old female patient.
Physics Case of the Day
Category CT
Authors: Kalpana M. Kanal, PhD, Puneet Bhargava, MB BS, DNB*,
Brent K. Stewart, PhD
University of Washington Medical Center, *Seattle Childrens Hospital, Seattle, WA
Discussion:
What is the breast dose from CT?
 Breast is a radiosensitive organ
 The dose to the breast from a CT PE examination is estimated to be 20-60 mGy, for
a CT coronary angiography examination to be 50-80 mGy and dose to the inferior part
of the breast for an abdominal CT examination is 10-20 mGy (Mettler et. al)
 In comparison, a two view mammogram imparts an average dose of 2 mGy to the
breast (Bushberg et. al)
Physics Case of the Day
Category CT
Authors: Kalpana M. Kanal, PhD, Puneet Bhargava, MB BS, DNB*,
Brent K. Stewart, PhD
University of Washington Medical Center, *Seattle Childrens Hospital, Seattle, WA
Discussion:
What is the breast dose from CT?
 Figure shows the radiation dose to the breast for a PE protocol using multidetector
CT scanner. Dose to breasts ranged from 35-42 mGy (Hurwitz et al, 2007)
Physics Case of the Day
Category CT
Authors: Kalpana M. Kanal, PhD, Puneet Bhargava, MB BS, DNB*,
Brent K. Stewart, PhD
University of Washington Medical Center, *Seattle Childrens Hospital, Seattle, WA
What is the breast cancer risk from
CT?
 The graph shows the % lifetime
attributable risk of breast cancer
incidence from a single standard CT
coronary angiography exam (would
be similar for CT PE exam)
The risk is higher for younger
women and decreases with age
Lifetime Attributable Risk
of Cancer Incidence %
Discussion:
Einstein et al, 2007
Physics Case of the Day
Category CT
Authors: Kalpana M. Kanal, PhD, Puneet Bhargava, MB BS, DNB*,
Brent K. Stewart, PhD
University of Washington Medical Center, *Seattle Childrens Hospital, Seattle, WA
Discussion:
What is the breast cancer
risk from CT?
The table shows the
lifetime attributable risk
(per 100,000 exposed
people) of breast cancer
for a 25 year old who
underwent a PE exam to
be 133 compared to 20 for
a 55 year old (Hurwitz et al,
2007)
Physics Case of the Day
Category CT
Authors: Kalpana M. Kanal, PhD, Puneet Bhargava, MB BS, DNB*,
Brent K. Stewart, PhD
University of Washington Medical Center, *Seattle Childrens Hospital, Seattle, WA
Discussion:
What can we do to reduce dose to the female breast?
 Consider and if possible use alternative imaging techniques such as US and MRI
to avoid radiation exposure to the breast all together
 Limit the field of view, if possible to minimize the amount of area irradiated. For
example, no need to include most of the lower chest in a CT abdomen study being
performed for evaluation of right lower quadrant abdominal pain
 Alter scan parameters, e.g., low dose technique using low kVp or mAs for follow
up scans of pulmonary nodules
Physics Case of the Day
Category CT
Authors: Kalpana M. Kanal, PhD, Puneet Bhargava, MB BS, DNB*,
Brent K. Stewart, PhD
University of Washington Medical Center, *Seattle Childrens Hospital, Seattle, WA
Discussion:
What can we do to reduce dose to the female breast?
 Avoid multiphase acquisition when not necessary, e.g., for most studies non-
contrast CT images are not necessary if post contrast CT is being performed
 Follow recommended follow up guidelines. For example, follow Fleischner
Society* guidelines for small pulmonary nodules and decrease cumulative
radiation exposure by delaying follow up if patient is low risk
 Use bismuth shields to protect the breasts of young female patients
*MacMahon H, Austin JHM, Gamsu G, et al. Guidelines for management of small
pulmonary nodules detected on CT Scans: A statement from the Fleischner
Society. Radiology 2005; 237: 395 - 400
Physics Case of the Day
Category CT
Authors: Kalpana M. Kanal, PhD, Puneet Bhargava, MB BS, DNB*,
Brent K. Stewart, PhD
University of Washington Medical Center, *Seattle Childrens Hospital, Seattle, WA
Discussion:
What can we do to reduce dose to
the female breast?
 Bismuth shielding (arrow) is
effective in reducing dose to the
breast
 At our institution, we have seen a
decrease of 37% in the breast dose
when using bismuth shields without
significant degradation in image
quality
Physics Case of the Day
Category CT
Authors: Kalpana M. Kanal, PhD, Puneet Bhargava, MB BS, DNB*,
Brent K. Stewart, PhD
University of Washington Medical Center, *Seattle Childrens Hospital, Seattle, WA
Discussion:
What can we do to reduce dose to
the female breast?
Fricke et al showed a 29%
reduction in breast dose using
bismuth shields on pediatric
patients without any significant
change in image quality
 Hohl et al showed a 32% breast
dose reduction using bismuth
shields without deterioration in
image quality

Physics Case of the Day
Category CT
Authors: Kalpana M. Kanal, PhD, Puneet Bhargava, MB BS, DNB*,
Brent K. Stewart, PhD
University of Washington Medical Center, *Seattle Childrens Hospital, Seattle, WA
References/Bibliography:
 Einstein et al.: JAMA, July 18, 2007 – Vol. 298, No. 3, Page 317.
 Hurwitz et al.: Radiology, December 2007 – Vol. 245, No. 3, Page 742.
 Mettler et al.: Radiology, July 2008 – Vol. 248, No. 1, Page 254.
 Fricke et al.: AJR, February 2003 – Vol. 180, Page 407.
 Bushberg et al.: The Essential Physics of Medical Imaging, 2nd Edition, 2002.
 Hohl et al.: Acta Radiologica, March 2006 – Vol. 27, No. 6, Page 562.
 http://radiology.rsnajnls.org/cgi/content/full/237/2/395