Y-90 Dosimetry with Monte Carlo Method: GATE Validation with STL Formatted Phantom

Abstract

In Y-90 treatment, it is important to implement patient-specific dosimetry. The study was aimed at creating an STL-based liver model phantom with multiple tumor mimics to test the GATE program and to perform Y-90 dosimetry with the Monte Carlo method. First, the liver model phantom with the outer dimensions of 22 x 14 x 8 cm(3) was made of plexiglass and two cylindrical tumor mimics were placed in it. (99mTc) activities with 62.9 MBq and 7 MBq were placed in both tumor mimics. Thermoluminescent dosimeters were used at 10 positions in the liver model phantom. Next, the same conditions were simulated in GATE and the absorbed doses were determined with DoseActors. After GATE validation, the absorbed doses were calculated for Y-90 source of 40.7 MBq. Based on this, the absorbed doses were estimated for the average amount of therapeutic Y-90 activity. The average instant absorbed doses in the liver model phantom for Tc-99m activities were found to be between 0.337 +/- 0.002 and 0.0059 +/- 0.0008 mu Gy/s via thermoluminescent dosimeters and between 0.367 +/- 0.002 and 0.0052 +/- 0.0003 mu Gy/s via GATE. When the Tc-99m results were compared, the mean overlap ratio and R-squared value were 10.68% and 0.9966, respectively. The mean absorbed doses in the first tumor mimic, the second tumor mimic and normal liver parenchymal tissue were 1350.0 +/- 7:7, 450.0 +/- 4.4 and 3.9 +/- 0.2 Gy for 1480 MBq therapeutic Y-90 activity. The GATE simulation showed significantly similar dosimetric results with the thermoluminescent dosimeter measurement for a liver dose calculation. As the tumor and liver dose estimation is a key limiting factor in Y-90 dosimetry, the practical application of the GATE simulation is an advantage for dose calculations and can improve the dosimetry.