Monte Carlo-Based Investigation of Microdosimetric Distribution of High Energy Brachytherapy Sources

Abstract

FLUKA-based Monte Carlo calculations were carried out to study microdosimetric distributions in air and in water for encapsulated high energy brachytherapy sources (60Co, 137Cs, 192Ir and 169Yb) by simulating a Tissue Equivalent Proportional Counter (Model LET1/2) having sensitive diameter of 1. 27 cm for a site size of 1 μm. The study also included microdosimetric distributions of bare sources. When the sources are in air, for a given source, the source geometry does not affect the y¯F and y¯D values significantly. When the encapsulated 192Ir, 137Cs and 60Co sources are in water, y¯F and y¯D values increase with distance in water which is due to degradation in the energy of photons. Using the calculated values of y¯D, relative biological effectiveness (RBE) was obtained for the investigated sources. When 60Co, 137Cs and 192Ir sources are in water, RBE increases from 1.03 ± 0.01 to 1.17 ± 0.01, 1.24 ± 0.01 to 1.46 ± 0.02 and 1.50 ± 0.01 to 1.75 ± 0.03, respectively, when the distance was increased from 3–15 cm, whereas for 169Yb, RBE is about 2, independent of distance in water.

Microdosimetry-based quality factors for ISO reference photon and beta sources: TOPAS Monte Carlo study

“…This table also includes ratio of the published values of 𝑦 𝑓 and 𝑦 𝑑 to the corresponding TOPAS-calculated values. The comparison shows that: (a) good agreement in 𝑦 𝑓 and 𝑦 𝑑 values with the published study by Chiriotti et al [35], Verma et al [36] and Chattaraj et al [37], (b) large deviation with 𝑦 𝑓 values of both the sources measured by Rollet et al [38]. Note that Rollet et al [38] used mini cylindrical TEPC whereas present study used LET-1/2 TEPC.…”

“…Note that both photons and electrons are available at the depth of interest. However, electrons below 400 keV will not be able to penetrate the wall of the TEPC as Continuous Slowing Down (CSDA) range of 400 keV electron is less than the thickness of the wall [37,44]. An auxiliary simulation was carried out to score secondary electron spectrum at 1 cm depth in ICRU phantom for 137 Cs source and it is found that only 4% electrons have kinetic energy above 400 keV.…”

Radiobiological comparison between Cobalt‐60 and Iridium‐192 high‐dose‐rate brachytherapy sources: Part I—cervical cancer

“…In agreement with this, it has been shown that the RBE values for 60 Co in sites of micrometer diameter were increasing with distance to the values greater than 1 (Chattaraj et al.) 46 …”

“…In agreement with this, it has been shown that the RBE values for 60 Co in sites of micrometer diameter were increasing with distance to the values greater than 1 (Chattaraj et al). 46 Besides the RBE discrepancies between 60 Co and 192 Ir, the different treatment times of the two sources could affect the BED or EUBED ratios. Until here, the comparisons were done considering both sources to be fresh that means the 60 Co treatment time is approximately two times greater than that of 192 Ir source.…”

Maximum RBE change in 192Ir, 125I, and 169Yb brachytherapy and the corresponding effect on treatment planning

“…In water, photons are attenuated close to the source, however, in air, low energy photons emitted from the 125 I source would easily reach the biological media (B-16 melanoma cells). In a recent study by Chattaraj et al [49]., Monte Carlo simulations were conducted in order to determine the lineal energy and subsequent RBE for several brachytherapy sources using the FLUKA software package. In this work, it was found that the RBE of 192 Ir increased from 1.50 (+/−0.01) to 1.75 (+/−0.03) as distance from the source was increased from 3 to 15 cm in water.…”