In vivo absorbed dose measurements with mini-TLDs--parameters affecting the reliability

Area of Science:

• Medical Physics
• Radiation Dosimetry

Background:

• Miniature thermoluminescent dosimeters (TLDs) are utilized for in vivo absorbed dose measurements in radionuclide therapies.
• Accurate dosimetry is critical for effective and safe radionuclide therapy.
• Previous studies highlight the need for detailed investigation into mini-TLD performance.

Purpose of the Study:

• To comprehensively evaluate the signal dependence of mini-TLDs on various parameters.
• To determine the accuracy of mini-TLDs for in vivo dosimetry applications.
• To assess the impact of environmental factors and tissue embedding on TLD measurements.

Main Methods:

• Rod-shaped CaSO4:Dy and LiF mini-TLDs were prepared and characterized.
• Fading effects were studied under different temperatures (4, 22, 37°C) in darkness after 60Co irradiation.
• Signal loss in gel and muscle tissue, supralinearity, and pH dependence were investigated.

Main Results:

• CaSO4:Dy mini-TLDs showed minimal fading in air, but signal loss increased with temperature in gel and muscle tissue.
• LiF mini-TLDs exhibited less signal loss in gel compared to CaSO4:Dy.
• Both dosimeter types showed supralinearity starting between 0.5-1 Gy for 60Co external irradiation.
• Significant pH dependence was observed, with CaSO4:Dy performing better at higher pH and LiF at neutral pH.

Conclusions:

• In vivo dosimetry with mini-TLDs necessitates meticulous handling and precise calibration to achieve accurate absorbed dose measurements.
• Without proper calibration, significant errors (up to 65% for CaSO4:Dy and 40% for LiF) can occur.
• Understanding parameter dependencies is crucial for reliable mini-TLD application in radionuclide therapy.