Technetium (99mTc) Macroaggregated Human Serum Albumin

This study aimed to determine the absorbed doses in the tumoral-liver and non-tumoral liver of hepatocellular carcinoma (HCC) patients undergoing radioembolization with Yttrium-90 (⁹⁰Y) resin microspheres, and compared with those derived from ^99mTc-MAA using the partition model.

A total of 42 HCC patients (28 males and 14 females, mean age 65 ± 11.51 years) who received 45 treatment sessions with ⁹⁰Y-microspheres between 2016 and 2021 were included. Pre-treatment ^99mTc-MAA and post-treatment ⁹⁰Y-bremsstrahlung SPECT/CT were acquired for each patient. Semi-automated segmentation of regions of interest (ROIs) was performed using MIM Encore software to determine the tumor-liver ratio (TLR) encompassing the liver volume, tumoral-liver, and lungs, and verified by both nuclear medicine physician and interventional radiologist. A partition dosimetry model was used to estimate the administered activity of ⁹⁰Y-microspheres and the absorbed doses to the tumoral-liver and non-tumoral liver. The student's paired t test and Bland-Altman plot were used for the statistical analysis.

The mean TLR values obtained from ^99mTc-MAA SPECT/CT and ⁹⁰Y-bremsstrahlung SPECT/CT were 4.78 ± 3.51 and 2.73 ± 1.18, respectively. The mean planning administered activity of ⁹⁰Y-microspheres based on ^99mTc-MAA SPECT/CT was 1.56 ± 0.80 GBq, while the implanted administered activity was 2.53 ± 1.23 GBq (p value < 0.001). The mean absorbed doses in the tumoral-liver estimated from ^99mTc-MAA and ⁹⁰Y-bremsstrahlung SPECT/CT were 127.44 ± 4.36 Gy and 135.98 ± 6.30 Gy, respectively. The corresponding mean absorbed doses in the non-tumoral liver were 34.61 ± 13.93 Gy and 55.04 ± 16.36 Gy.

This study provides evidence that the administered activity of ⁹⁰Y-microspheres, as estimated from ⁹⁰Y-bremsstrahlung SPECT/CT, was significantly higher than that estimated from ^99mTc-MAA SPECT/CT resulted in increased absorbed doses in both the tumoral-liver and non-tumoral liver. However, ^99mTc-MAA SPECT/CT remains a valuable planning tool for predicting the distribution of ⁹⁰Y-microspheres in liver cancer treatment.

A 67-year-old woman presented with shortness of breath and a ventilation/perfusion scan was performed. Initial images demonstrated mismatched bilateral apical defects that would be classified as high probability for pulmonary emboli. However, it was unusual that the defects were only in the bilateral apices. Investigation discovered that 99mTc-MAA was administered while the patient was in a seated position. Repeat scan the following day with the patient in the correct, supine, position during 99mTc-MAA administration demonstrated no defects. In this case, incorrect patient positioning could have resulted in an incorrect diagnosis of pulmonary emboli and inappropriate treatment of the patient.