Monte Carlo dosimetric characterization of a new high dose rate Yb brachytherapy source and independent verification using a multipoint plastic scintillator detector

Abstract

Purpose: A prototype 169 Yb source was developed in combination with a dynamic rotating platinum shield system (AIM-Brachy) to deliver intensity modulated brachytherapy (IMBT). The purpose of this study was to evaluate the dosimetric characteristics of the bare/shielded 169 Yb source using Monte Carlo (MC) simulations and perform an independent dose verification using a dosimetry platform based on a multipoint plastic scintillator detector (mPSD). Methods: The TG-43U1 dosimetric parameters were calculated for the source model using Rapid-BrachyMCTPS. Real-time dose rate measurements were performed in a water tank for both the bare/ shielded source using a custom remote afterloader. For each dwell position, the dose rate was independently measured by the three scintillators (BCF-10, BCF-12, and BCF-60). For the bare source, dose rate was measured at distances up to 3 cm away from the source over a range of 7 cm along the catheter. For the shielded source, measurements were performed with the mPSD placed at 1 cm from the source at four different azimuthal angles (0 , 90 , 180 , and 270). Results: The dosimetric parameters were tabulated for the source model. For the bare source, differences between measured and calculated along-away dose rates were generally below 5-10%. Along the transverse axis, deviations were, on average (range), 3.3% (0.6-6.2%) for BCF-10, 1.7% (0.9-2.9%) for BCF-12, and 2.2% (0.3-4.4%) for BCF-60. The maximum dose rate reduction due to shielding at a radial distance of 1 cm was 88.8 AE 1.2%, compared to 83.5 AE 0.5% as calculated by MC. Conclusions: The dose distribution for the bare/shielded 169 Yb source was independently verified using mPSD with good agreement in regions close to the source. The 169 Yb source coupled with the partial-shielding system is an effective technique to deliver IMBT.

Applying the column generation method to the intensity modulated high dose rate brachytherapy inverse planning problem

“…The shield is not thick enough to attenuate the intensity of the conventional 192 Ir source, hence this radionuclide cannot be used for prostate IMBT. A radionuclide with lower energy than 192 Ir, namely 169 Yb was chosen (Famulari et al 2020b). The dynamic shield system combined with the source model presented in Famulari et al (2020a) were used in the simulations performed in this study with 169 Yb as the active source.…”

“…In 2013, Webster et al (2013) published a study regarding dynamic modulated brachytherapy for rectal cancer by translating and rotating a tungsten alloy shield during the treatment. Following this study, two separate studies by Adams et al (2014) and Famulari et al (2020b) for prostate cancer and additional studies by Dadkhah et al (2015) and Morcos and Enger (2020), Morcos et al (2021) for cervical cancer investigated rotating shield brachytherapy. All these studies showed improved dose distributions when IMBT was compared to conventional brachytherapy.…”