Sestamibi (Breast Imaging)

10.10.1 Radiopharmaceutical

• [^99mTc]Tc-2-methoxyisobutylisonitrile ([^99mTc]Tc-sestamibi)

10.10.2 Uptake mechanism / biology of the tracer

[^99mTc]Tc-MIBI is a lipophilic cation that crosses the cell membrane and penetrates reversibly into the cytoplasm via thermodynamic driving forces and then irreversibly passes the mitochondrial membrane using a different electrical gradient regulated by a high negative inner membrane potential. The cancer cells, with their greater metabolic turn-over, are characterized by a higher electrical gradient of mitochondrial membrane thus determining an increased accumulation of [^99mTc]Tc-MIBI compared to normal cells.

10.10.3 Indications

Approved by the European Medicines Agency (EMA):

[^99mTc]Tc-sestamibi is indicated as a second line diagnostic drug after mammography in evaluating breast lesions in patients with an abnormal mammogram or a palpable breast mass.

10.10.4 Contra-indications

• The only absolute contra-indication is pregnancy.
• It is not recommended to interrupt breast feeding although an interruption of 4 h during which one meal is discarded can be advised to be on the safe side [3].

10.10.5 Clinical performances

Overall sensitivity in the detection of primary breast cancer:

• 94% with overall specificity at 84% respectively.
• In the patients with palpable masses, the sensitivity of scintimammography was 97% and the specificity was 84%.
• In patients with non-palpable masses, the sensitivity was 35% and the specificity 100%.
• For the detection of axillary lymph node involvement, the sensitivity and specificity of scintimammography were 68% and 93%, respectively [336].

10.10.6 Activities to administer

The suggested activity to administer is:

• [^99mTc]Tc-MIBI in adults: 740-1110 MBq

In paediatric nuclear medicine, the activities should be modified according to the EANM paediatric dosage card (https://www.eanm.org/publications/dosage-calculator/). The minimum recommended activity to administer is 80 MBq.

10.10.7 Dosimetry

The effective dose for [^99mTc]Tc-MIBI in adults is 9 µSv/MBq. The organ with the highest absorbed dose is the gallbladder wall: 39 µGy/MBq.

The range in effective dose in adults for [^99mTc]Tc-MIBI is: 6.7-10 mSv per procedure.

Caveat:
“Effective Dose” is a protection quantity that provides a dose value related to the probability of health detriment to an adult reference person due to stochastic effects from exposure to low doses of ionizing radiation. It should not be used to quantify the radiation risk for a single individual associated with a particular nuclear medicine examination. It is used to characterize a certain examination in comparison to alternatives, but  it should be emphasized that if the actual risk to a certain patient population is to be assessed, it is mandatory to apply risk factors (per mSv) that are appropriate for the gender, the age distribution and the disease state of that population."

10.10.8 Interpretation criteria/major pitfalls

Any focus of MIBI uptake > breast background is rated as positive.

10.10.9 Patient preparation

None. Fasting state is optional to reduce physiologic hepatic extraction ameliorating tracer availability.

10.10.10 Methods

The detailed recommendations are available in the EANM Oncology Guidelines.