Optimization of ^99mTc-MDP Dose Based on Renal Function:

Development of an Individualized Protocol Using Femoral Background Values

Abstract

Background: In patients with reduced renal function, delayed clearance of ^99mTc-MDP leads to unnecessary radiation exposure. This study aimed to develop a practical dose optimization protocol based on renal function using femoral background values as a surrogate marker for residual body activity.

Methods: We retrospectively analyzed 159 patients who underwent bone scintigraphy from January to December 2023. Patients were stratified into five CKD groups based on eGFR. Dose-normalized femoral background counts were compared between groups using Kruskal-Wallis and Dunn’s tests. A dose reduction model was constructed based on background value ratios relative to the normal renal function group (G1).

Results: The study included 114 breast cancer and 45 prostate cancer patients. Femoral background values showed significant negative correlation with eGFR （ρ＝－0.557, p<0.001m）. Compared to G1, normalized background values increased by 12.7％ in G2, 45.4％ in G3a, 101.6％ in G3b, and 129.0％ in G4-G5. No significant correlation was found between dose and bone-to-background ratio （ρ＝－0.573, p<0.001）, demonstrating that renal function, not dose, determines image contrast. Proposed dose reduction rates were 16.1％ for G2, 35.4％ for G3a, 47.2％ for G3b, and 54.8％ for G4-G5.

Conclusion: Renal function-based dose optimization using femoral background values can reasonably reduce radiation exposure while maintaining diagnostic image quality. Theoretical analysis demonstrated that dose increase is ineffective due to biological saturation phenomena. This protocol requires no special equipment and is easily implementable in clinical practice.