UNCERTAINTIES IN THE FRACTIONATION AND OPTIMIZATION OF RADIOEMBOLIZATION WITH SIR-SPHERES®
Víctor González González,
Spain
PO-1780
Abstract
UNCERTAINTIES IN THE FRACTIONATION AND OPTIMIZATION OF RADIOEMBOLIZATION WITH SIR-SPHERES®
Authors: Víctor González1, Pedro Matias Liñan1, Aida López1, Alfredo Montes1, Carmen Escalada1
1Hospital universitario Puerta de Hierro de Majadahonda, Radiophysics, Madrid, Spain
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Purpose or Objective
Hepatic radioembolization treatments with SIR-Spheres® consist of the administration, through the hepatic artery, of microspheres labeled with Y-90, a beta emitter of 2.27 MeV. The process introduces uncertainties that will affect the radiation doses that finally received by professionals and patients. Our aim is to identify and quantify the aspects of fractionation that can influence the optimization of both the preparation and the treatment itself.
Material and Methods
The prescribed activity for each treatment volume is extracted by splitting the delivery vial, which contains the treatment with SIR-Spheres®. These microspheres, which are preferentially deposited in hypervascularized lesions, have diameters between 20 and 70 µm and are supplied in a vial with 5 ml of aqueous suspension and 3 GBq of activity. For this purpose, different samples of known activity and volume have been measured with a Veenstra VDC-404 activimeter calibrated for Y-90.
Results
It has been observed that, for the same sample, the measurement increases rapidly with time and the same activity measures more in smaller volumes. In the first case, the progressive decantation of the microspheres reduces the thickness of attenuation that the radiation must pass through, increasing the measurement up to 11%. In the second, a greater volume implies more thickness of attenuation, reducing the measurement up to 6%. On the other hand, the appearance of a concentration gradient in the sample makes the activity obtained depend on the calculated extraction volume, the depth of the end of the needle inside the vial and the time elapsed since it has been shaken. Correcting differences between expected and achieved activity may require repeated manipulation of the vials.
Conclusion
In conclusion, we observe that the geometric and temporal intrinsic factors to fractionation can increase the preparation time, increasing the operator dose, and introduce appreciable uncertainties in the value of the activity administered to the patient. Both cases work against the optimization principle.