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E1228. Investigation of Technetium Complexes as Potential Mammographic Contrast Agents
Authors
  1. Aaron Hodes; Jacobi Medical Center; Montefiore Medical Center
  2. Francesco D'errico; Yale School of Medicine
  3. Rafael Fernandez; Jacobi Medical Center
  4. Jessica Rosenblum; Jacobi Medical Center
  5. David Cheng; Jacobi Medical Center
Objective:
Patients with dense breast tissue have greater risk of higher cancer burden at diagnosis and developing interval cancer compared to patients with predominantly fatty breast tissue. Detecting cancer in patients with dense breast tissue using mammography and supplemental ultrasound is quite challenging. Iodinated contrast agents can improve detection but risk false positives. Technetium (Tc) complexes with the metastable 99 isotope (99m-Tc) can incidentally breast cancer on nuclear medicine studies and are studied as a screening tool; however, the radiation dose from 99m-Tc and lower spatial resolution of gamma cameras compared to mammography limits a wider use. In fact, Tc k-edge (21.044 keV) is close to rhodium's characteristic x-ray energy and in the emission spectrum of units with a tungsten anode and rhodium and silver filters. Also, complexes with the stable 99-Tc isotope (99-Tc) derived from the decay of 99m-Tc might be a targeted contrast agent due to the ligands' affinity for breast cancer and the absorption coefficient of Tc for mammography x-rays. Our hypothesis was to see if 99-Tc complexes derived from 99m-Tc at standard or higher doses could serve as mammography contrast agents.

Materials and Methods:
Two 99m-pertechnetate solutions with known radioactivity assessed at the time of arrival to our institution, i.e. 45 mCi (0.9 mL in 3 mL syringe), or known before export from the pharmacy, i.e. 6600 mCi (4.8 mL in 5 mL syringe), were secured in the radiopharmaceutical lab until radioactivity was similar to background. Controls were 4.8 mL of air and 4.8 mL of 0.9% saline in 5 mL syringes. All syringes were radiographed on the same mammography unit (Selenia Dimensions Mammography System, Hologic Inc.) inside a styrofoam container (thickness 3.8 cm) and then in water bath sealed in a plastic bag (thickness 1.8 cm). Signal to noise ratio was measured at 20-30 kVp using the automatic exposure control function of the digital mammography unit.

Results:
No qualitative difference in radiodensity between the saline or 99-Tc solutions could be seen. Quantitative differences in attenuation were only seen in the water bag with higher 99-Tc concentration. Minimum theoretical Tc mass with a detectability similar to iodine in contrast-enhanced mammography was calculated from the minimum recommended iodine dose (90 mL of 300 mg I/mL solution, about 27 g iodine). Since Tc attenuates 3.5x more than iodine in the 20-30 keV range and 1.16 x 10^22 atoms 99m-Tc/mCi 99m-Tc, the calculated equivalent initial 99m-Tc dose and mass would be 3.16x10^21 mCi and 6.0 g Tc, respectively.

Conclusion:
Tc compounds at standard doses do not qualitatively or quantitatively improve solution contrast, whereas higher amounts of 99-Tc may serve as mammographic contrast agents. However, our Tc dose assessment did not account for different distributions of iodinated and 99-Tc-complexes to breast cancer, which are not documented to the best of our knowledge. Future studies may focus on the fraction of injected 99-Tc dose to breast cancer and on discovering compounds with multiple Tc moieties to improve detection sensitivity.