Evaluation of scintigraphic images of simulated tumors with different volumes in a liver phantom

Objective: Yttrium-90 (⁹⁰Y) radioembolization and the use of Technetium-99m macroaggregated albumin (⁹⁹ᵐTc-MAA) for pre-dosimetry are routinely effective methods in the treatment of unresectable liver tumors. This study aims to evaluate the impact of tumor volume variation and tumor proximity on scintigraphic image quality and dosimetry, and to objectively analyze these effects using contrast and contrast-to-noise ratio (CNR) parameters. Materials and Methods: In this experimental study, a specially designed liver phantom containing four simulated tumors with diameters of 1 cm, 2 cm, 3 cm, and 5 cm was used. The tumors and the surrounding liver parenchyma-mimicking areas were filled with ⁹⁹ᵐTc at a ratio of 4.88:1. The phantom was imaged in a water tank using standard clinical protocols for both planar and SPECT scintigraphy. Regions of interest (ROIs) were drawn over the lesions on the images to calculate contrast, CNR, and tumor doses. Results: In SPECT images, as tumor diameter increased, tumor-to-normal liver ratio (T/N) per milliliter, contrast, CNR, and tumor doses also increased. Tumor doses for 1 cm and 5 cm diameter lesions were found to be 6.9 Gy/ml and 13.43 Gy/ml, respectively. Similarly, T/N ratios, contrast, and CNR values calculated from planar imaging also increased with tumor size; however, the increase in tumor doses was found to be relatively lower. Discussion and Conclusion: This study analyzed the mutual effect of ROI counts in the presence of small and multiple tumors in ⁹⁹ᵐTc-MAA pre-dosimetry for liver tumors. It was observed that smaller tumors (1–3 cm) located near larger tumors were affected by spillover from the larger lesions, resulting in artificially elevated ROI counts and consequently overestimated dose calculations. In conclusion, the presence of larger lesions may influence dosimetric evaluations of smaller (1–3 cm) tumors, potentially leading to inaccurate dose assessments. Keywords: ⁹⁹ᵐTc-MAA scintigraphy, ⁹⁰Y radioembolization, pre-dosimetry, image quality, tumor doses