Monte Carlo and experimental dosimetric study of the mHDR-v2 brachytherapy source

Abstract

The conventional treatment planning system (TPS) gives analytical calculations with ± 15 to 20% dose, which may lead to over exposure of critical organs or under dose of target. It is to obtain dose distribution parameters of nucletron high dose rate (HDR) microselectron v2 (mHDR-v2) 192 Ir brachytherapy source by experiment and by calculated study using Monte Carlo (MC) EGSnrc code, and to find the similarity between them, and with any past study. To validate data, another MC GEANT4 study done in this work on the same source is also presented. Different software of the computer e.g. paint, excel, etc are employed for preparation of figures and graphs. The measured study of the source was done using an in-air ionization chamber, water phantom, and measurement set-up, while the calculated study was done by modeling the set up of the measured study by using the MC EGSnrc and GEANT4. Mean and probability are used in calculation of average values, and calculation of the uncertainties in result and discussion. The measured and calculated values of dose rate constant, radial dose function, and 2D anisotropy function were found to be in agreement with each other as well as with published data. The results of this study can be used as input to TPS.

Monte Carlo study of dosimetric parameters and dose distribution effect of inhomogeneities and source position of GammaMed Plus source

“…[5] In this calculated study, the uncertainties of dose rate have been evaluated according to the recommendations of TG-43U1 considering the type A or statistical uncertainty due to the MC simulation of photon histories in dose rate and air kerma These results are found in good agreement with literature data. [8][9][10] Figure 7 illustrates the data and graph between strength simulation and the type B uncertainty due to the contribution of underlying cross section data and that arising from the source geometrical model. In the simulation in water, the uncertainty in dose rate along the transverse axis is approximately equal to 0.5 % except along the longitudinal axis where it has reached to more or less 1%.…”

“…Pantelis et al [7] show that if the source position near or far from the surface of patient is not taken into consideration, the central breast dose is overestimated of the order of 5%, and all other points of the breast is overestimated 10% in HDR brachytherapy of breast. Similarly, the effect of inhomogeneities like cortical bone and air, and source position on dose distribution is done by Chandola et al [8,9] and Terribilini et al [10] Apart from radiation−tissue interaction study, MC simulation is used to solve various physical problems. MC simulation calculations are based on random sampling techniques and are capable to collect the information based on large number of histories.…”

Dosimetric intercomparison of permanent Ho-166 seed's implants and HDR Ir-192 brachytherapy in breast cancer

“…29 Brachytherapy source strength is specified in terms of air kerma rate at a point in air taken at the perpendicular bisector of the source segment, being the product of air kerma rate times the distance to a point, usually 1 m. Air kerma strength conversion for 192 Ir of 1 Gy m 2 h −1 is equal to 8.991 MBq. [29][30][31] A conversion factor of 1.0891 × 10 −5 U to 1 Bq of Ir-192 is also found. In addition, the recommended quantity for specifying a beta-emission source is the reference absorbed dose rate in water at a reference point of 2 mm from the seeds taken at the transverse direction from the source's longitudinal axis at its center.…”

“…These conversion factors are generated using a combination of Monte-Carlo calculations and absorbed dose rate experimental measurements. [29][30][31] …”

Physics-aspects of dose accuracy in high dose rate (HDR) brachytherapy: source dosimetry, treatment planning, equipment performance and in vivo verification techniques

“…Chandola et al . [41] have compared results of MC codes, EGSnrc and GEANT4, alongside validation by ionisation chamber measurements, for the Nucletron mHDR-v2 Ir-192 brachytherapy source, finding the two codes gave comparable results in TG-43 dosimetric data: agreement of dose rate constant within 1%, radial dose function within 2% up to 5 cm and within 6% up to 10 cm and 2D anisotropy function within 2% for polar angles 25° < θ < 140°, up to 6% outside this range. MC has also been used for evaluation of clinically relevant parameters, rather than simply dose distribution around an isolated HDR source, such as Sureka et al .…”