Parameters to consider for measurements of absorbed doses in vivo with mini-thermoluminescent dosimeters.
BACKGROUND
For systemic radiation therapy, i.e., radioimmunotherapy, there is a demand for direct methods of measuring the absorbed dose in vivo. One such method is the use of mini-thermoluminescent dosimeters (TLDs). This paper reports an investigation of the sensitivity of tissue implanted mini-TLDs (calcium sulfate:Dy, 0.2 x 0.4 x 5.0 mm).


METHODS
After being irradiated with cobalt-60, the mini-TLDs were left for as long as 9 days in air, gel, and muscle tissue.


RESULTS
There was an extensive signal loss, which increased with time, except in air. After 9 days in gel or muscle tissue at room temperature, the signal was decreased to one third of its original value. The dosimeters needed to be kept in constant darkness. There was a strong pH dependence, with a loss of sensitivity of 63% at a pH below 5, which got smaller at higher pH values and reached 10% at pH = 10.


CONCLUSIONS
When using mini-TLDs in vivo, one must calibrate the dosimeters in similar milieus, unless the position of the dosimeters in tissue after implantation can be monitored for temperature, pH, and liquid flow.
Strand
S E
SE
Radiation Physics Department, Lund University, Sweden.
Strandh
M
M
D000818:Animals; D003037:Cobalt Radioisotopes; D006863:Hydrogen-Ion Concentration; D009132:Muscles; D016499:Radioimmunotherapy; D012680:Sensitivity and Specificity; D013819:Thermoluminescent Dosimetry
D003037:Cobalt Radioisotopes