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Advances in Radiotherapy
& Nuclear Medicine Beta radiation doses from Y-90 microsphere

In this study, estimations of the beta dose rates alongside for understanding the dose distribution around individual
the radial distance of a microsphere containing the microspheres, which is a building block for modeling more
Yttrium-90 radionuclide were performed. Yttrium-90 has complex systems involving multiple microspheres.
a physical half-life of 2.7 days and emits beta particles with
a maximum energy of 2.28 MeV (mean energy of 0.933 2. Materials and methods
MeV) and with a mean range of 0.25 cm. These properties In this study, we consider a unique sphere containing
make it a suitable beta emitter to be used in brachytherapy the Y-90 radioisotope distributed uniformly over its
treatment of hepatic tumors. 2-12 external surface, as well as SIR-spheres microspheres
In this work, we present initial calculations of dose which are manufactured from resin [poly(styrene-co-
rates around a microsphere of radius R loaded with the divinylbenzene)] and biocompatible material, and are
intended for permanent application (SIR-Spheres , Sirtex
®
Y-90 radionuclide uniformly distributed on its exterior 2
surface (Figure 1). Two approaches were used to carry Medical Ltd., Sydney, Australia).
out the estimations: first by means of Monte Carlo (MC) In clinical practice, Y-90 microspheres are
simulations using the PENELOPE code, version 2014; 15,16 often distributed heterogeneously within the liver.
and second by means of the beta-point dose function Understanding the dose distribution from a single
formalism. 17-19 A Fortran code (some versions of compiler microsphere allows for better modeling of scenarios where
can be freely downloaded from the web) was developed clusters of microspheres form regions of varying radiation
to perform the numerical integration of the beta-point intensities. This knowledge can improve the accuracy of
dose function. 20,21 A comparison between the calculations dose calculations in heterogeneous distributions, leading
obtained by MC simulation and the results obtained by to more precise treatment planning.
means of the beta-point dose function was made, and a 2.1. Monte carlo calculation
good agreement was found between the results considering
these two calculation methods. In this work, the dose rates along the radial distances of
the resin Y-90 microsphere were simulated using the
It should be noticed that the dosimetric evaluation of PENELOPE code, version 2014. 15,16 With the PENELOPE
a single microsphere provides essential insights into the code, it is possible to simulate negative beta particles,
fundamental behavior of the beta radiation emitted by Y-90 positrons, and photons cascades initiated by a primary
at a micro-scale. This foundational knowledge is crucial incident particle.
All simulated materials were generated using the
material.f program, which is part of the PENELOPE
package. Once the information about the materials is
known, the program interface prompts the user to enter
relevant information such as the number of chemical
elements in the material, their atomic numbers, their
stoichiometry or mass fraction per element and density.
Once the main data is provided, the software calculates the
average excitation energy, the estimated oscillator strength,
and the plasmon energy.
In the in.in input file, the necessary parameters
were defined for the simulation to occur as expected,
considering the variables of the simulated problem
and computational time optimization criteria. When
building this file, important aspects were defined, such
as the type of simulated particle and its energies, the
spatial arrangement of the emitting source and the
target material, the geometry file name that contains the
information about the emitting body and its dimensions,
the emission direction, the desired output files, among
Figure 1. The geometry of the sphere with the Yttrium-90 radionuclide other important parameters, such as simulation time and
distributed on its surface used throughout calculations number of simulated stories.

Volume 2 Issue 3 (2024) 2 doi: 10.36922/arnm.3639