Abstract
Purpose: Transarterial 90Y microspheres radioembolization is emerging as a multidisciplinary promising therapeutic modality for primary and metastatic cancer in the liver. Actually two different type of microspheres are used, whose main characteristic is the different density of activity (activity per microsphere). In this paper the effect due to the possible different distribution of the microspheres in a target is presented and discussed from a macrodosimetric point of view. Material and methods: A 100 g virtual soft-tissue target region has been builded. The administered activity was chosen to have a target average absorbed dose of 100 Gy and the number of 90Y microspheres needed was calculated for two different activity-per-microsphere values (2500) Bq/microsphere and 50 Bq/microsphere, respectively). The spheres were randomly distributed in the target and the Dose Volume Histograms were obtained for both. The cells surviving fractions (SF) for four different values of the radiobiological parameter α were calculated from the Linear - Quadratic model. Results: The DVH obtained are very similar and the SF is almost equal for both the activity-per- microsphere values. Conclusions: This macrodosimetric approach shows no radiobiological difference between the glass and resin microspheres. Thus the different number of microspheres seems to have no effect when the number of spheres is big enough that the distance between the spheres in the target can be considered small compared to the range of thei β-particles of 90Y.
Highlights
The relativistic doppler effectSuppose two reference frames A and B with identical emitters and detectors move with constant velocities against each other, but their velocities against a fixed point are not known
The special theory of relativity (STR) experiments produce results that are in accordance with theory
The STR shows that the classical physical formulas must be multiplied by ɣ, but as discussed above this cannot be accomplished with the LT
Summary
Suppose two reference frames A and B with identical emitters and detectors move with constant velocities against each other, but their velocities against a fixed point are not known. These are the classical Doppler formulas but with a correction factor ɣ that compensates the lack of knowledge of the absolute velocities of A and B It is based on the geometric mean of the observations in A and B. The Lorentz-transformed physical values are geometric means [4] as a result of the simultaneous movement of frames A and B in opposite directions The advantage of this interpretation is that we can understand the STR intuitively, but the consequences of this interpretation are significant. In the Relativistic Doppler effect, the factor ɣ describes the situation that only the relative velocity v between A and B is known In this case the relativistic change of frequency f is not real either in the observed system. It has become possible to test the above concept regarding the ɣ correction with the geometric mean
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