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Author |
Gimenez-Alventosa, V.; Antunes, P.C.G.; Vijande, J.; Ballester, F.; Perez-Calatayud, J.; Andreo, P. |
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Title |
Collision-kerma conversion between dose-to-tissue and dose-to-water by photon energy-fluence corrections in low-energy brachytherapy |
Type |
Journal Article |
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Year |
2017 |
Publication |
Physics in Medicine and Biology |
Abbreviated Journal |
Phys. Med. Biol. |
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Volume |
62 |
Issue |
1 |
Pages |
146-164 |
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Keywords  |
Monte Carlo; dosimetry; low-energy seed; collision-kerma; mass energy-absorption coefficients; energy-fluence correction factor |
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Abstract |
The AAPM TG-43 brachytherapy dosimetry formalism, introduced in 1995, has become a standard for brachytherapy dosimetry worldwide; it implicitly assumes that charged-particle equilibrium (CPE) exists for the determination of absorbed dose to water at different locations, except in the vicinity of the source capsule. Subsequent dosimetry developments, based on Monte Carlo calculations or analytical solutions of transport equations, do not rely on the CPE assumption and determine directly the dose to different tissues. At the time of relating dose to tissue and dose to water, or vice versa, it is usually assumed that the photon fluence in water and in tissues are practically identical, so that the absorbed dose in the two media can be related by their ratio of mass energy-absorption coefficients. In this work, an efficient way to correlate absorbed dose to water and absorbed dose to tissue in brachytherapy calculations at clinically relevant distances for low-energy photon emitting seeds is proposed. A correction is introduced that is based on the ratio of the water-to-tissue photon energy-fluences. State-of-the art Monte Carlo calculations are used to score photon fluence differential in energy in water and in various human tissues (muscle, adipose and bone), which in all cases include a realistic modelling of low-energy brachytherapy sources in order to benchmark the formalism proposed. The energy-fluence based corrections given in this work are able to correlate absorbed dose to tissue and absorbed dose to water with an accuracy better than 0.5% in the most critical cases (e.g. bone tissue). |
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Address |
[Gimenez-Alventosa, Vicent; Antunes, Paula C. G.; Vijande, Javier; Ballester, Facundo] Univ Valencia, Dept Atom Mol & Nucl Phys, E-46100 Burjassot, Spain, Email: vijande@uv.es |
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Iop Publishing Ltd |
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English |
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ISSN |
0031-9155 |
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Notes |
WOS:000391567700001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
2923 |
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Author |
Gimenez-Alventosa, V.; Vijande, J.; Ballester, F.; Perez-Calatayud, J. |
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Title |
Transit dose comparisons for Co-60 and Ir-192 HDR sources |
Type |
Journal Article |
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Year |
2016 |
Publication |
Journal of Radiological Protection |
Abbreviated Journal |
J. Radiol. Prot. |
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Volume |
36 |
Issue |
4 |
Pages |
858-864 |
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Keywords |
Monte Carlo; dosimetry; HDR brachytherapy; transit dose |
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Abstract |
The goal of this study is to evaluate the ambient dose due to the transit of high dose rate (HDR) Co-60 sources along a transfer tube as compared to Ir-192 ones in a realistic clinical scenario. This goal is accomplished by evaluating air-kerma differences with Monte Carlo calculations using PENELOPE2011. Scatter from both the afterloader and the patient was not taken into account. Two sources, mHDR-v2 and Flexisource Co-60, (Elekta Brachytherapy, Veenendaal, the Netherlands) have been considered. These sources were simulated within a standard transfer tube located in an infinite air phantom. The movement of the source was included by displacing their positions along the connecting tube from z = – 75 cm to z = + 75 cm and combining them. Since modern afterloaders like Flexitron (Elekta) or Saginova (BEBIG GmbH) are able to use equally 192Ir and 60Co sources, it was assumed that both sources are displaced with equal speed. Typical HDR source activity content values were provided by the manufacturer. 2D distributions were obtained with type-A uncertainties (k = 2) less than 0.01%. From those, the air-kerma ratio Co-60/Ir-192 was evaluated weighted by their corresponding typical activities. It was found that it varies slowly with distance (less than 10% variation at 75 cm) but strongly in time due to the shorter half-life of the 192Ir (73.83 d). The maximum ratio is located close to the tube. It reaches a value of 0.57 when the typical activity of the sources at the time when they were installed by the vendor was used. Such ratio increases up to 1.28 at the end of the recommended working life (90 d) of the Ir-192 source. Co-60/Ir-192 air-kerma ratios are almost constant (0.51-0.57) in the vicinity of the source-tube with recent installed sources. Nevertheless, air-kerma ratios increase rapidly (1.15-1.29) whenever the Ir-192 is approaching the end of its life. In case of a medical event requiring the medical staff to access the treatment room, these ratios indicate that the dosimetric impact on the medical team will be lower, with a few exceptions, in the case of Co-60-based HDR brachytherapy as compared to Ir-192-based one when typical air-kerma strength values are considered. |
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Address |
[Gimenez-Alventosa, Vicent; Vijande, Javier; Ballester, Facundo] Univ Valencia, Dept Atom Mol & Nucl Phys, E-46100 Burjassot, Spain, Email: javier.vijande@uv.es |
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Publisher |
Iop Publishing Ltd |
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English |
Summary Language |
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ISSN |
0952-4746 |
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Notes |
WOS:000386436100002 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
no |
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Call Number |
IFIC @ pastor @ |
Serial |
2839 |
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Author |
Assam, I.; Vijande, J.; Ballester, F.; Perez-Calatayud, J.; Poppe, B.; Siebert, F.A. |
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Title |
Evaluation of dosimetric effects of metallic artifact reduction and tissue assignment on Monte Carlo dose calculations for I-125 prostate implants |
Type |
Journal Article |
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Year |
2022 |
Publication |
Medical Physics |
Abbreviated Journal |
Med. Phys. |
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Volume |
49 |
Issue |
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Pages |
6195-6208 |
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Keywords |
metallic artifact reduction; Monte Carlo dosimetry; post-implant CT; prostate brachytherapy; tissue assignment schemes; voxelized virtual patient model |
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Abstract |
Purpose Monte Carlo (MC) simulation studies, aimed at evaluating the magnitude of tissue heterogeneity in I-125 prostate permanent seed implant brachytherapy (BT), customarily use clinical post-implant CT images to generate a virtual representation of a realistic patient model (virtual patient model). Metallic artifact reduction (MAR) techniques and tissue assignment schemes (TAS) are implemented on the post-implant CT images to mollify metallic artifacts due to BT seeds and to assign tissue types to the voxels corresponding to the bright seed spots and streaking artifacts, respectively. The objective of this study is to assess the combined influence of MAR and TAS on MC absorbed dose calculations in post-implant CT-based phantoms. The virtual patient models used for I-125 prostate implant MC absorbed dose calculations in this study are derived from the CT images of an external radiotherapy prostate patient without BT seeds and prostatic calcifications, thus averting the need to implement MAR and TAS. Methods The geometry of the IsoSeed I25.S17plus source is validated by comparing the MC calculated results of the TG-43 parameters for the line source approximation with the TG-43U1S2 consensus data. Four MC absorbed dose calculations are performed in two virtual patient models using the egs_brachy MC code: (1) TG-43-based D-w,w-TG(43), (2) D-w,D-w-MBDC that accounts for interseed scattering and attenuation (ISA), (3) D-m,D-m that examines ISA and tissue heterogeneity by scoring absorbed dose in tissue, and (4) D-w,D-m that unlike D-m,D-m scores absorbed dose in water. The MC absorbed doses (1) and (2) are simulated in a TG-43 patient phantom derived by assigning the densities of every voxel to 1.00 g cm(-3) (water), whereas MC absorbed doses (3) and (4) are scored in the TG-186 patient phantom generated by mapping the mass density of each voxel to tissue according to a CT calibration curve. The MC absorbed doses calculated in this study are compared with VariSeed v8.0 calculated absorbed doses. To evaluate the dosimetric effect of MAR and TAS, the MC absorbed doses of this work (independent of MAR and TAS) are compared to the MC absorbed doses of different I-125 source models from previous studies that were calculated with different MC codes using post-implant CT-based phantoms generated by implementing MAR and TAS on post-implant CT images. Results The very good agreement of TG-43 parameters of this study and the published consensus data within 3% validates the geometry of the IsoSeed I25.S17plus source. For the clinical studies, the TG-43-based calculations show a D-90 overestimation of more than 4% compared to the more realistic MC methods due to ISA and tissue composition. The results of this work generally show few discrepancies with the post-implant CT-based dosimetry studies with respect to the D-90 absorbed dose metric parameter. These discrepancies are mainly Type B uncertainties due to the different I-125 source models and MC codes. Conclusions The implementation of MAR and TAS on post-implant CT images have no dosimetric effect on the I-125 prostate MC absorbed dose calculation in post-implant CT-based phantoms. |
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Address |
[Assam, Isong; Siebert, Frank-Andre] UKSH, Clin Radiotherapy Radiooncol, Campus Kiel, Kiel, Germany, Email: Isong.Assam@uksh.de |
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Publisher |
Wiley |
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English |
Summary Language |
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ISSN |
0094-2405 |
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Notes |
WOS:000835807200001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5321 |
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Author |
Granero, D.; Candela-Juan, C.; Vijande, J.; Ballester, F.; Perez-Calatayud, J.; Jacob, D.; Mourtada, F. |
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Title |
Technical Note: Dosimetry of Leipzig and Valencia applicators without the plastic cap |
Type |
Journal Article |
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Year |
2016 |
Publication |
Medical Physics |
Abbreviated Journal |
Med. Phys. |
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Volume |
43 |
Issue |
5 |
Pages |
2087 - 4pp |
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Keywords |
Leipzig applicators; Valencia applicators; skin brachytherapy; Monte Carlo; dosimetry |
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Abstract |
Purpose: High dose rate (HDR) brachytherapy for treatment of small skin lesions using the Leipzig and Valencia applicators is a widely used technique. These applicators are equipped with an attachable plastic cap to be placed during fraction delivery to ensure electronic equilibrium and to prevent secondary electrons from reaching the skin surface. The purpose of this study is to report on the dosimetric impact of the cap being absent during HDR fraction delivery, which has not been explored previously in the literature. Methods: GEANT4 Monte Carlo simulations (version 10.0) have been performed for the Leipzig and Valencia applicators with and without the plastic cap. In order to validate the Monte Carlo simulations, experimental measurements using radiochromic films have been done. Results: Dose absorbed within 1 mm of the skin surface increases by a factor of 1500% for the Leipzig applicators and of 180% for the Valencia applicators. Deeper than 1 mm, the overdosage flattens up to a 10% increase. Conclusions: Differences of treating with or without the plastic cap are significant. Users must check always that the plastic cap is in place before any treatment in order to avoid overdosage of the skin. Prior to skin HDR fraction delivery, the timeout checklist should include verification of the cap placement. (C) 2016 American Association of Physicists in Medicine. |
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Address |
[Granero, D.] Hosp Gen Univ, Dept Radiat Phys, ERESA, Valencia 46014, Spain, Email: dgranero@eresa.com |
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Amer Assoc Physicists Medicine Amer Inst Physics |
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English |
Summary Language |
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Series Editor |
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ISSN |
0094-2405 |
ISBN |
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Conference |
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Notes |
WOS:000378924200010 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
2753 |
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Author |
Granero, D.; Vijande, J.; Ballester, F.; Rivard, M.J. |
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Title |
Dosimetry revisited for the HDR Ir-192 brachytherapy source model mHDR-v2 |
Type |
Journal Article |
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Year |
2011 |
Publication |
Medical Physics |
Abbreviated Journal |
Med. Phys. |
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Volume |
38 |
Issue |
1 |
Pages |
487-494 |
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Keywords |
Ir-192; brachytherapy; dosimetry; TG-43; PSS model; MCNP5; PENELOPE2008; GEANT4 |
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Abstract |
Purpose: Recently, the manufacturer of the HDR Ir-192 mHDR-v2 brachytherapy source reported small design changes (referred to herein as mHDR-v2r) that are within the manufacturing tolerances but may alter the existing dosimetric data for this source. This study aimed to (1) check whether these changes affect the existing dosimetric data published for this source; (2) obtain new dosimetric data in close proximity to the source, including the contributions from 192Ir electrons and considering the absence of electronic equilibrium; and (3) obtain scatter dose components for collapsed cone treatment planning system implementation. Methods: Three different Monte Carlo (MC) radiation transport codes were used: MCNP5, PENELOPE2008, and GEANT4. The source was centrally positioned in a 40 cm radius water phantom. Absorbed dose and collision kerma were obtained using 0.1 mm (0.5 mm) thick voxels to provide high-resolution dosimetry near (far from) the source. Dose-rate distributions obtained with the three MC codes were compared. Results: Simulations of mHDR-v2 and mHDR-v2r designs performed with three radiation transport codes showed agreement typically within 0.2% for r >= 0.25 cm. Dosimetric contributions from source electrons were significant for r<0.25 cm. The dose-rate constant and radial dose function were similar to those from previous MC studies of the mHDR-v2 design. The 2D anisotropy function also coincided with that of the mHDR-v2 design for r >= 0.25 cm. Detailed results of dose distributions and scatter components are presented for the modified source design. Conclusions: Comparison of these results to prior MC studies showed agreement typically within 0.5% for r >= 0.25 cm. If dosimetric data for r<0.25 cm are not needed, dosimetric results from the prior MC studies will be adequate. c 2011 American Association of Physicists in Medicine. |
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Address |
[Granero, Domingo] Hosp Gen Univ, Dept Radiat Phys, ERESA, E-46014 Valencia, Spain, Email: dgranero@eresa.com |
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Publisher |
Amer Assoc Physicists Medicine Amer Inst Physics |
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Language |
English |
Summary Language |
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Original Title |
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Abbreviated Series Title |
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Series Volume |
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ISSN |
0094-2405 |
ISBN |
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Conference |
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Notes |
ISI:000285769800050 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
557 |
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