Radiology: New breast imaging modalities may raise cancer risk
Recently introduced breast imaging modalities, including breast-specific gamma imaging (BSGI) and positron emission mammography (PEM), are linked with higher cancer risk per study compared with the risks associated with mammography and extend cancer risk to radiosensitive organs, according to a study published online Aug. 24 in Radiology.

The FDA has recently approved BSGI and PEM, resulting in introduction of both modalities as diagnostic adjuncts that also may be used for breast cancer screening in the U.S. market.

The study examined recent literature and Biologic Effects of Ionizing Radiation (BEIR) VII age-dependent risk data to compare radiation doses and lifetime attributable risks (LARs) of radiation-induced cancer incidence and mortality from breast imaging modalities involving the use of ionizing radiation, including BSGI, PEM and mammography, explained R. Edward Hendrick, PhD, clinical professor of radiology at the University of Colorado-Denver, School of Medicine.

Two-view digital mammography and screen-film mammography produce average mean glandular radiation doses of 3.7 and 4.7 mGy, respectively, wrote Hendrick, which are associated with LARs of fatal breast cancer of 1.3 and 1.7 cases per 100,000 women aged 40 years at exposure. Annual digital or film-based screening in women aged 40 to 80 years produces a LAR of fatal breast cancer of 20 to 25 cases in 100,000 women, reported Hendrick.

BSGI entails administration of 740-1100 MBq of 99mTc-sestamibi. Effective dose estimates for 1100 MBq of 99mTc-sestamibi range from 8.9 to 9.4 mSv, with the large intestine wall, kidneys, bladder wall and gallbladder wall receiving the highest doses. At that dose range, BEIR VII-derived risk estimates indicate an LAR of induced fatal cancer of 26 to 39 cases in 100,000 women aged 40 years at exposure. Thus, the age-specific risk of radiation-induced cancer death from a single BSGI study with 740-1100 MBq of 99mTc-sestamibi dose is 20 to 30 times greater than that from a single digital mammography study on a 40-year old woman, noted Hendrick.

PEM involves administration of 370 MBq of FDG with the bladder, uterus and ovaries receiving the highest doses. BEIR VII-derived risk estimates indicate an LAR of fatal cancer of about 30 cases in 100,000 women aged 40 years. “The age-specific risk of radiation-induced cancer death from a single PEM study compared with that from a single digital mammogram is more than 20 times greater at age 40 years, more than 75 times greater at 60 years, and more than 175 times greater at age 80 years,” wrote Hendrick.

He pointed out that BSGI and PEM irradiate all body organs while mammography exposes only breast tissue, so the risks from BSGI and PEM extend to cancer in a number of radiosensitive organs. In the case of mammography, the risk of radiation-induced cancer is limited to breast cancer.

Although both BSGI and PEM have high sensitivity to breast cancer, clinical studies are limited, noted Hendrick, who suggested that thorough clinical investigation is needed before the modalities are employed for screening. “The results indicate that BSGI and PEM are not good candidate procedures for breast cancer screening because of the associated higher risks for cancer induction per study compared with the risks associated with existing modalities such as mammography, breast ultrasound and breast MRI,” concluded Hendrick.

However, “the benefit-to-risk ratio for BSGI and PEM may be different in women known to have breast cancer, in whom additional information about the extent of disease may better guide treatment,” he wrote, who recommended that physicians who use the studies as a diagnostic adjunct should clearly explain their risks and benefits to patients.