Indian Journal of Nuclear Medicine
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ORIGINAL ARTICLE
Year : 2015  |  Volume : 30  |  Issue : 2  |  Page : 122-127

Deviation in the predefined calibration factors of the dose calibrators and the associated inaccuracy in the radioactivity measurements of beta-gamma emitters


1 Department of Nuclear Medicine and PET, PGIMER, Chandigarh, India
2 Department of Biophysics, Panjab University, Chandigarh, India

Correspondence Address:
Prof. Baljinder Singh
Department of Nuclear Medicine and PET, PGIMER, Chandigarh - 160 012
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-3919.152972

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Aim: To determine whether the predefined calibration factors of the dose calibrators can provide accurate radioactivity measurements of beta-gamma emitters used in routine therapeutic nuclear medicine procedures. Materials and Methods: Two models of dose calibrators were used in the present study for radioactivity measurements of 153 Sm ethylenediamine-N, N, N', N'- tetrakis methylene phosphonic acid (EDTMP) and 177 Lu (EDTMP). A known (precalibrated) activity of each of the two beta emitters received by us from our National Supplier for administration to the patients with extensive bony metastases for bone pain palliation, was used for experiments. Results: When we used the manufacturers' provided dial setting of 450 × 10, each of the dose calibrators underestimated the radioactivity of 177 Lu by about 9.0%. Dial settings of 403 × 10 and 408 × 10 for 177 Lu on CRC-15R and CRC-ultra dose calibrators respectively were calculated experimentally using an iterative approach. The radioactivity measurements made at these settings provided an excellent agreement with the specified values. Likewise, a dial setting of 230 for each of the two dose calibrators was calculated for 153 Sm, which provided a good agreement between the experimentally derived radioactivity values and the certified values. A deviation of ± 5.0% was observed when radioactivity of 177 Lu and 153 Sm was measured over a wide range (4.0 MBq to 2.1 GBq) for time intervals equivalent to 4.5 half-lives of each of the two radionuclides. A deviation of ± 5% was observed when radioactivity was counted in different dilution volumes and in syringes of varying size. Conclusion: These variations could lead to a cumulative error of about 20.0% toward the inaccuracy in the radioactivity measurements of the beta-gamma emitters and thus predefined calibration factors of the dose calibrators may require experimental re-setting of these parameters and periodic checking to provide accurate radioactivity estimates of beta-gamma emitters in a given clinical setting.


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