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The activity and nuclide data of lutetium-177

23.08.2012

The beta-ray emitting radionuclide lutetium-177 is used for tumour treatment in nuclear medicine. By the emissions of photons from gamma transitions, it can also be used for imaging procedures so that the therapeutic benefit is supplemented.

The use of the isotope in medicine requires, however, a reliable basis for activity determinations. For this reason, PTB has developed measurement procedures already several years ago to determine the activity of 177Lu solutions [1]. Nuclide data have also already been determined earlier at PTB to contribute to a better understanding of the radioactive isotope.

Recently, the results of an international comparison for activity determination on a 177Lu solution distributed by NIST have been published [2]. PTB was one of the eleven participants in the comparison and has, as in the case of former measurements [1], used the 4πβ-γ coincidence method and the CIEMAT/NIST method in which liquid scintillation counters are used. In addition, PTB has – for the first time – used the TDCR procedure (TDCR= triple-to-double-coincidence ratio) which is also based on liquid scintillation counting. The combination of the three measurement procedures allowed the smallest relative standard measurement uncertainty of the comparison (0.19 %) to be achieved. The result also agrees excellently with the mean value of all participants in the comparison.

In addition, the solution measured within the scope of the comparison as well as two other 177Lu solutions were used to determine nuclide data. The combination of the exact activity measurements and of measurements of the photon emissions by means of well calibrated semiconductor spectrometers allowed photon emission probabilities to be determined. The results [3] are in very good agreement with former values from PTB [1]. A special challenge is the impurity by the meta-stable 177mLu which – on its part – reproduces 177Lu, and which can often not be neglected.

The half-life of 177Lu was also determined again. This time, the result was derived from measurements with a liquid scintillation counter and is in good agreement with former measurements; the measurement uncertainty of the new value is, however, somewhat larger. Nevertheless, the additional value improves the data basis and the newly recommended value for the half-life amounts to T½ = (6.6457 ± 0.0030) d [3].

The reproducibility of the activity measurements at PTB is also confirmed by relative measurements with 4π ionization chambers which quasi allow the former absolute measurements to be conserved. At PTB, the ionization chamber measurements of a radionuclide are always carried out together with measurements of a long-lived 226Ra standard so that possible variations in the response are largely compensated. As the response depends, among other things, on the measurement geometry used, the latest absolute measurements were also used to determined calibration factors of a new ampoule type which has been used at PTB only since 2005. Thereby, PTB will also in future be able to carry out activity determinations by means of calibrated ionization chambers and to guarantee, in this way, the dissemination of the unit of activity for 177Lu. By this, an important prerequisite is complied with for quality-assured applications in nuclear medicine.

Literature

  1. Schötzig, U., Schrader, H., Schönfeld, E., Günther, E., Klein, R.:
    Standardisation and decay data of 177Lu and 188Re.
    Applied Radiation and Isotopes 55 (2001) 89-96.
  2. Zimmerman, B. E., Altzitzoglou, T., Antohe, A., Arinc, A., Bakhshandeiar, E., Bergeron, D. E., Bignell, L., Bobin, C., Capogni, M., Cessna, J. T., Cozzella, M. L., da Silva, C. J., De Felice, P., Dias, M. S., Dziel, T., Fazio, A., Fitzgerald, R., Iwahara, R., Jaubert, F., Johansson, L., Keightley, J., Koskinas, M. F., Kossert, K., Lubbe, J., Luca, A., Mo, L., Nähle, O., Ott, O., Paepen, J., Pommé, S., Sahagia, M., Simpson, B. R. S., Silva, F. F. V., van Ammel, R., van Staden, M. J., van Wyngaardt, W. M. and Yamazaki, I. M.:
    Results of an international comparison for the activity measurement of 177Lu.
    Applied Radiation and Isotopes 70 (2012) 1825-1830.
  3. Kossert, K., Nähle, O. J., Ott, O., Dersch, R.:
    Activity determination and nuclear decay data of 177Lu.
    Applied Radiation and Isotopes 70 (2012) 2215-2221.