Razi Journal of Medical Sciences

    Background: In this survey the absorbed dose by kidneys, bladder, liver and ovaries with ^99mTc-EC (^99mTc Ethylene dicysteine) renal scintigraphy was measured and compared with the absorbed dose from ^99mTc-DTPA (^99mTc - Dietheylne Triamine Penta-Acid), which often is used in renal scintigraphy.

Methods: In this applicable study, we used a water phantom with geometrical sizes similar to that of human body and composed of thorax and hip. Then in accordance with International Committee on Radiation Protection ICRP -23, we placed kidney, liver, bladder and ovary phantoms in to the thorax and hip parts. For dosimetry 30 cubical Lithium fluoride chips (TLD-100) were used.

By using different values of ^99mTc-EC and ^99mTc-DTPA distributed in different phantom parts, the absorbed doses in kidneys, liver, bladder and ovaries were measured. Then by measuring skin dose in the region of kidneys, bladder, liver and ovaries in 20 female patients (10 patients for each radioisotope) that were under renal scan, the absorbed doses of above mentioned organs using phantom results were calculated. Statistical software used was SPSS V.16 and statistical data analysis was done by One sample Kolmogorov-Smirnov and t-tests.

Results: The results of skin and organ absorbed doses of kidneys, liver, bladder and ovaries showed a good linear regression. The relationship between organ dose and skin dose with total activity varied linearly. The results of organ absorbed dose in patients that were under renal scan with both radiopharmaceuticals showed:

- Bladder absorbed dose with ^99mTc-DTPA and ^99mTc-EC respectively were: 4.42±0.98 mrad/mCi, 2.91±0.74 mrad/mCi (p=0.001).

-Liver absorbed dose with ^99mTc-DTPA and ^99mTc-EC respectively were: 2.44±0.44 mrad/mCi, 1.58±0.019 mrad/mCi (p=0.000).

-Right kidney absorbed dose with ^99mTc-DTPA and ^99mTc-EC respectively were: 4.04±1.06 mrad/mCi, 2.67±0.036 mrad/mCi (p=0.003).

- Left kidney absorbed dose with ^99mTc-DTPA and ^99mTc-EC respectively were: 4.11±0.93 mrad/mCi, 2.60±0.14 mrad/mCi (p=0.000).

-Ovaries absorbed dose with ^99mTc-DTPA and ^99mTc-EC respectively were: 2.55±0.28 mrad/mCi, 1.62±0.025 mrad/mCi (p=0.000).

Conclusion: The results of this study showed that in patients under renal scan with ^99mTc-EC, absorbed dose by kidneys, liver, bladder and ovaries is considerably lower than those with ^99mTc-DTPA. Also as ^99mTc-EC has several other advantages such as: easily prepared, cheap, lower hepatic uptake, produces high quality images and has high renal excretion as compared to ^99mTc-DTPA, thus it could be used more in radioisotopic renal scan in nuclear medicine clinics.