Molecular Breast Imaging: Administered Activity Does Not Require Adjustment Based on Patient Size

Area of Science:

• Nuclear Medicine
• Radiology
• Medical Imaging

Background:

• Molecular breast imaging (MBI) is a nuclear medicine procedure utilizing ^99mTc-sestamibi.
• Standard MBI protocols at some institutions administer a fixed activity (e.g., 300 MBq) regardless of patient size.
• Adjusting administered activity or imaging time based on patient size is common in other nuclear medicine procedures to ensure adequate counts.

Purpose of the Study:

• To investigate the influence of patient body size and breast thickness on the uptake of ^99mTc-sestamibi in breast tissue during MBI.
• To determine if current MBI protocols require adjustments in administered activity for larger patients.

Main Methods:

• Retrospective analysis of 200 patients undergoing clinical MBI with 300 MBq of ^99mTc-sestamibi.
• Calculation of exact administered activity, breast thickness, body mass index, body surface area, and lean body mass.
• Measurement of count density (cts/cm²/MBq) in breast tissue using regions of interest.
• Statistical analysis using Spearman correlation to assess relationships between count density and patient/breast measurements.

Main Results:

• No correlation was found between MBI count density and compressed breast thickness (r_s = 0.06; P = 0.37).
• Weak negative correlations were observed between count density and patient height, weight, body mass index, body surface area, and lean body mass.
• These correlations suggest that larger body size does not significantly impact ^99mTc-sestamibi uptake in breast tissue for MBI.

Conclusions:

• ^99mTc-sestamibi uptake in breast tissue during MBI is not significantly influenced by patient body size or compressed breast thickness.
• Standard administered activity of 300 MBq is likely sufficient for MBI across different patient sizes.
• Dose adjustments for larger patients in MBI are probably unnecessary, simplifying protocol standardization.