Wednesday Case of the Day

1
Wednesday Case of the Day
Physics CT
Kalpana M. Kanal, PhD, Puneet Bhargava, MBBS,
DNB, Brent K. Stewart, PhD
University of Washington Medical Center, Seattle
Childrens Hospital, Seattle, WA

• History
• CT pulmonary angiography (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 the arrow and
  why it is being used for this exam.

2
Wednesday Case of the Day
Physics CT
Kalpana M. Kanal, PhD, Puneet Bhargava, MBBS,
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.

3
Wednesday Case of the Day
Physics CT
Kalpana M. Kanal, PhD, Puneet Bhargava, MBBS,
DNB, Brent K. Stewart, PhD
University of Washington Medical Center, Seattle
Childrens Hospital, Seattle, WA

• Discussion
• What is the breast dose from CT?
• The breast is a radiosensitive organ.
• The dose to the breast from a CT PE examination
  is estimated to be 20-60 mGy, the dose for a CT
  coronary angiography examination is estimated to
  be 50-80 mGy, and the dose to the inferior part
  of the breast for an abdominal CT examination is
  estimated to be 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).

4
Wednesday Case of the Day
Physics CT
Kalpana M. Kanal, PhD, Puneet Bhargava, MBBS,
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 a multidetector CT
  scanner. Dose to breasts ranged from 35-42 mGy.
  (Reprinted, with permission, from Hurwitz et al.)

5
Wednesday Case of the Day
Physics CT
Kalpana M. Kanal, PhD, Puneet Bhargava, MBBS,
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 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.

Einstein et al, 2007.
6
Wednesday Case of the Day
Physics CT
Kalpana M. Kanal, PhD, Puneet Bhargava, MBBS,
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 that the lifetime attributable
  risk (per 100,000 exposed people) of breast
  cancer for a 25-year-old who underwent a PE exam
  is 133, compared to 20 for a 55-year-old.
  (Reprinted, with permission, from Hurwitz et al.)

7
Wednesday Case of the Day
Physics CT
Kalpana M. Kanal, PhD, Puneet Bhargava, MBBS,
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 altogether.
• Limit the field of view, if possible, to
  minimize the amount of area irradiated. For
  example, there is no need to include most of the
  lower chest in an abdominal CT study being
  performed for evaluation of right-lower-quadrant
  abdominal pain.
• Alter scan parameters (eg, low-dose technique
  using low kVp or mAs for follow-up scans of
  pulmonary nodules).

8
Wednesday Case of the Day
Physics CT
Kalpana M. Kanal, PhD, Puneet Bhargava, MBBS,
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
  (eg, for most studies, noncontrast CT images are
  not necessary if postcontrast CT is being
  performed).
• Follow recommended follow-up guidelines. For
  example, follow Fleischner Society guidelines
  for small pulmonary nodules and to decrease
  cumulative radiation exposure by delaying
  follow-up if the 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
  2005237395-400.

9
Wednesday Case of the Day
Physics CT
Kalpana M. Kanal, PhD, Puneet Bhargava, MBBS,
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.

10
Wednesday Case of the Day
Physics CT
Kalpana M. Kanal, PhD, Puneet Bhargava, MBBS,
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 by 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.

11
Wednesday Case of the Day
Physics CT
Kalpana M. Kanal, PhD, Puneet Bhargava, MBBS,
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/23
  7/2/395