Mammography screening

» What is mammography screening?

Screening for breast cancer is used to detect cancers at an early stage when they can be treated most effectively. The first stage in breast screening involves an X ray (mammogram) of the breast. 

Usually 2 images of each breast are obtained and a radiologist examines the images. Mammography can detect very small changes in breast tissue density and thus detect cancer well before these changes can be felt by either the woman or the doctor. Additional images might be required if there is a problem with the image quality (anatomical positioning, artifacts, or sub-optimum technique factors) or if a special technique such as magnification is required to increase the visibility of specific objects or structures (like microcalcifications) that can be signs of cancer. 

If the mammography shows signs of cancer, it will usually be followed by a biopsy procedure performed by either the radiologist with image guidance or by a surgeon. To improve diagnostic accuracy, it is important to bring previous images, if taken, for comparison purposes. Ultrasound is often used to determine if a palpable abnormality is cystic or solid. This is often used in younger women. Other modalities (such as MRI) are also used in some institutions for diagnostic purposes but not usually for screening purposes.

» What is the radiation dose received in mammography screening?

A typical mammographic screening examination involving 2 views of each breast (total 4 mammograms) delivers a dose of between 3 and 5 mGy to the glandular tissue. Dose expresses the X-ray energy absorbed in a specific tissue. In the breast it is the glandular tissue that is the most radiosensitive.

The usual procedure is to estimate and express the dose as the average dose or more specifically the mean glandular dose (MGD) within each breast. Women with smaller than average breasts will receive a lower MGD. Doses are higher for women with larger breasts. Any additional images that might be required will add to the dose received.

» Is screening justified from a radiation protection perspective?

Yes, when the norms of mammographic screening are adhered to.

The calculated risk of breast cancer associated with the use of ionizing radiation is much lower than the number of cancers detected in a well run, quality assured breast screening programme. In other words, the benefits of breast cancer screening far exceed the radiation risks.

» Why is mammography not used for routine screening of young women?

Mammography is not as effective in younger women for detecting cancer in the pre-menopausal breast. 

In pre-menopausal women, the composition of breast tissue makes it harder to detect problems. Screening with mammography might be appropriate for some women in high risk groups (e.g. women with close family members who have had breast cancer at a young age or have other clinical indications). For these women screening is justified from a radiation protection perspective as they have an elevated risk of breast cancer. Effective screening programmes give emphasis to post-menopausal women and women at a higher than average risk of breast cancer.

» Why is mammography screening recommended for older women?

The risk of breast cancer generally increases with age. Older women should be encouraged to participate in a breast screening programme.