Model-Based Evaluation of Point-Source Approximation Error for Extended Radionuclide Sources in Nuclear Medicine

Area of Science:

• Medical Physics
• Radiation Safety
• Nuclear Medicine

Background:

• Accurate external radiation exposure estimation is crucial in nuclear medicine for safety and compliance.
• Point-source models are common but can be inaccurate for extended radioactive sources.

Purpose of the Study:

• To evaluate point-source approximation errors for various extended source geometries.
• To provide correction factors and guidance for nuclear medicine exposure assessments.

Main Methods:

• Calculated dose rates using Tc-99m gamma constant for line, disc, slab, and cylindrical sources.
• Expressed errors using geometry- and attenuation-dependent parameters.
• Derived analytical correction factors for slab sources.

Main Results:

• Point-source models can overestimate exposure by up to 100% for non-attenuating sources when dimensions exceed distance.
• Errors were <5% when source dimension-to-distance ratio was <1.
• Cylindrical models showed substantial overestimation for patient-scale sources compared to point-source estimates.

Conclusions:

• Point-source approximation introduces significant errors for extended sources in nuclear medicine.
• Correction factors and model-selection guidance are provided for accurate exposure assessments.
• The study aids in enhancing occupational safety and regulatory compliance in nuclear medicine.