Mammography:
Risks and benefits
Zahra Anjomani
Content
• Overview of Breast Cancer
• Mammography machine
• Risks and Benefits of Mammography
Overview of Breast Cancer
• The most common form
of cancer among women
• The second most
common cause of cancer
related mortality
• 1 of 8 women (12.2%)
• One third of women
with breast cancer die
from breast cancer
Risk Factors for Breast Cancer
• Female (1% male)
• Aging
• Relative (mother or
sister)
• Menstrual history
– early on set
– late menopause
• Child birth
– After the age of 30
Risk Factors for Breast Cancer
• Radiation exposure
• Breast disease
– Atypical Hyperplasia
– Intraductal carcinoma in situ
– Intralobular carcinoma in situ
• Obesity
• Diet
– Fat
– Alcohol
Genetics
•
•
•
•
BRCA-1
BRCA-2
P53, Rb-1
Her-2/neu,
c-erB2, c-myc
Anatomy
• Breasts vary in
size and shape!
• Consist of
glandular, fat,
and muscle
tissue
Anatomy
• Lymphatic vessels of breast drain into two
sets of nodes
– Axillary lymph nodes, laterally
– Internal mammary lymph nodes, medially
• Axillary nodes are often evaluated on
mammograms
Breast Cancer
•
There are two general categories
of breast cancer:
– Non-invasive (or in situ)
cancer confined to lobules or ducts
– Invasive
cancer spread to fatty connective
tissue
Staging of Breast Cancer
• The American Joint Committee on
Cancer (AJCC) has designated staging by
TNM
– T= tumor size
– N = lymph node involvement
– M = metastasis
Stage 1
• Tumor < 2.0 cm in
greatest dimension
• No nodal
involvement (N0)
• No metastases (M0)
Stage II
• 2.0< Tumor < 5 cm
or
• Ipsilateral axillary
lymph node (N1)
• No Metastasis (M0)
Stage III
• Tumor > 5 cm (T3)
• or ipsilateral axillary lymph nodes fixed
to each other or other structures (N2)
• involvement of ipsilateral internal
mammary nodes (N3)
• Inflammatory carcinoma (T4d)
Stage IV
(Metastatic breast cancer)
• Any T
• Any N
• Metastasis (M1)
Abnormal signs and symptoms
•
•
•
•
•
Puckering
Dimpling
Retraction
Nipple discharge
Thickening of skin
or lump or “knot”
• Retracted nipple
Principles Of Breast Cancer
• Pt.s in early stages respond well to treatment
• Patients with advanced disease do poorly
• Earlier diagnosis, better chance of survival
• Mammography is tool for early detection
History of Mammography
• 1913
– First attempt at mammography
• 1950
– First utilized low kVp and high mAs techniques
• 1960
– Development of xero-mammography
• 1990
– Screen film mammography was accepted
How does a mammography machine work?
Differential attenuation
• Small x-ray attenuation differences between
normal and cancerous tissues in the breast require
the use of x-ray equipment specially designed to
optimize breast cancer detection
• Attenuation differences between these tissues is
highest at very low x-ray energies (10 to 15 keV)
and is poor at higher energies (>35 keV)
System design
• Because of the risks of ionizing radiation,
techniques that minimize dose and optimize image
quality are essential, and have led to:
–
–
–
–
–
–
Refinement of dedicated x-ray equipment
Specialized x-ray tubes
Compression devices
Antiscatter grids
Phototimers
Detector systems
Cathode & filament design
• Mammographic x-ray tubes typically have dual
filaments in a focusing cup that produces 0.3 and
0.1 mm nominal focal spot sizes
– Minimize geometric blurring and maintain spatial
resolution necessary for microcalcification detection
Anode design
• Mammographic x-ray tubes use a rotating anode
• Molybdenum is the most common anode material;
rhodium & tungsten also used
• Source to image distance (SID) of 65 cm requires
the effective anode angle to be at least 20º to avoid
field cutoff for the 24 x 30 cm field area
Heel effect
• Lower x-ray intensity on the anode side of the
field at short SID is very noticeable
• Positioning the cathode over the chest wall of the
patient and the anode over the nipple achieves
better uniformity of the radiation transmitted
through the breast
• Orientation of the tube in this fashion also
decreases the equipment bulk near the patient’s
head for easier positioning
Beam quality considerations
• Computer modeling studies show that the optimal
x-ray energy to achieve high subject contrast and
the lowest radiation dose would be a
monoenergetic beam of 15 to 25 keV, depending
on breast composition and thickness
• Optimal x-ray energy is achieved by the use of
specific x-ray tube target materials and added
filtration materials
Filtration
• Inherent filtration must be kept low;
beryllium (Z = 4) is used for the tube port
• Added tube filters of the same element as
the target reduce the low- and high-energy
x-rays in the spectrum and allow
transmission of the characteristic x-ray
energies
Compression Device
• Compression
decreases
thickness of breast,
magnification and
scatter
• Increases contrast
• Reduces motion
unsharpness
• Reduces dosage
Compression Device
• Made of firm plastic
• Amount of compression: between
25 and 40 pounds pressure
• Compression may be
uncomfortable!
Screen-Film Systems
• Mammography cassettes contain a single
screen
• Film is single emulsion
• Occasionally, extended time processing is
used
– (reduces dose and increases contrast)
Digital mammography
• Replaces the screen and film with a charged
couple device (CCD)
• CCD converts light into electrons
• Electrons are sent to the computer where it
is converted into a digital format and a
radiographic image is produced on the CRT
Digital versus Conventional
Courtesy: Magee-Women’s Hospital of UPMC
Craniocaudal Projection
Mediolateral Oblique
Radiography Of Augmented Breast
(implants)
• 8 projections must
be obtained (2x4)
Mammographer’s Nightmare
Benefits versus Risks from
Mammography
•
When breast cancer is detected before it has spread to lymph nodes or
to other parts of the body, the 5-year survival rate is 97%
•
Early detection and early treatment can improve the chances of
surviving breast cancer. Currently, mammography is the best tool
available to detect the earliest warning signs of breast cancer
Types of Mammography
I) Diagnostic mammography
Performed on patients with symptoms
II) Screening mammography
Performed as a preventative measure
Usually done between the ages of 40 and 50
Risk v. Benefit
• The most important benefit of
mammographic examinations is detecting
breast cancer at an early stage and perhaps
reducing mortality
I) Screening programs
• Breast cancer screening programs rely on x-ray
mammography because it is a low-cost, lowradiation-dose procedure with the sensitivity to
detect early-stage breast cancer
• American Cancer Society
• National Cancer Institute
• American College of Radiology
encourage mammograms every
two years for women ages 40 to 49
Screening program for woman between 40
and 50 is still controversial
Screening mammography
Risk factors
• false-positive
– mean greater expense
• false-negative
– a rate of missed tumors
Likelihood of saving a life
Four categories of cancers found by mammography :
• a) cancers that are so easy to treat that a later detection would
have produced the same total cure
• b) cancers so aggressive that even "early" detection is too late
• c) cancers that are so slow-growing that the woman would
die of other causes before the cancer produces symptoms
• e) cancers whose treatment outcome improves as a result of
earlier detection.
Only between 3% and 13% of breast cancers
fall into the last category
II) Diagnostic Mammogram
• For woman presenting with clinical
evidence of breast disease, palpable mass or
other symptom
• Uses specific projections to
– Rule out cancer
– Demonstrate suspicious area seen on screening
mammogram
Risk of Causing Breast Cancer by
Mammography
• Mammograms use doses of ionizing x-rays
to create images. One of the potential risks
of mammography is the radiation exposure
associated with mammography.
Dose from Mammography:
• American College of Radiology
The average dose at accredited mammography
facilities was reported to be 1.38 mGy per
view, or typically double this dose (2.8 mGy)
per examination (because 2 views of each
breast are typically obtained)
Dose-Incidence Relationship
The question of whether there is a practical
threshold at low doses for radiation-induced
breast cancer has been evaluated by a
number of researchers, including Land et
al., who inferred that the best statistical fit
to the available data was a linear doseresponse curve
Modifiers of dose response
• exposure before the age of 20 years carries
the greatest risk.
• a history of benign breast disease
• exposure to radiation while pregnant
• genetic factors
The magnitude of risk per unit dose depends
strongly on when radiation exposure occurs
Summery
• The most important benefit
– detecting breast cancer at an early stage.
• For asymptomatic women under 35 the risk of breast cancer is
not high enough to justify the risk of radiation exposure.
• The evidence shows that there is small benefit in terms of early
detection in screening of that woman between 40 and 50.
• Ionizing radiation is a breast cancer risk factor
– the risk increases linearly with dose.
– Age at exposure is an important factor of the radiationrelated breast cancer risk.
Risk v. Benefit
• Breast cancer in United States in 2007 (estimated):
New cases: 192,370 (female); 1,910 (male)
Deaths: 40,170 (female); 440 (male)
• Us population 306 million in 2007- 133 deaths /million
• Mortality risk from mammography induced radiation is 5
deaths/ million pts. using screen film mammography
• More risky to refuse mammography!
THE END