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Title: A dosimetric comparison of {sup 169}Yb versus {sup 192}Ir for HDR prostate brachytherapy

Abstract

For the purpose of evaluating the use of {sup 169}Yb for prostate High Dose Rate brachytherapy (HDR), a hypothetical {sup 169}Yb source is assumed with the exact same design of the new microSelectron source replacing the {sup 192}Ir active core by pure {sup 169}Yb metal. Monte Carlo simulation is employed for the full dosimetric characterization of both sources and results are compared following the AAPM TG-43 dosimetric formalism. Monte Carlo calculated dosimetry results are incorporated in a commercially available treatment planning system (SWIFT{sup TM}), which features an inverse treatment planning option based on a multiobjective dose optimization engine. The quality of prostate HDR brachytherapy using the real {sup 192}Ir and hypothetical {sup 169}Yb source is compared in a comprehensive analysis of different prostate implants in terms of the multiobjective dose optimization solutions as well as treatment quality indices such as Dose Volume Histograms (DVH) and the Conformal Index (COIN). Given that scattering overcompensates for absorption in intermediate photon energies and distances in the range of interest to prostate HDR brachytherapy, {sup 169}Yb proves at least equivalent to {sup 192}Ir irrespective of prostate volume. This has to be evaluated in view of the shielding requirements for the {sup 169}Yb energies thatmore » are minimal relative to that for {sup 192}Ir.« less

Authors:
; ; ; ; ;  [1];  [2];  [3];  [4]
  1. Nuclear and Particle Physics Section, Physics Department, University of Athens, Panepistimioupolis, Ilisia, 157 71 Athens (Greece)
  2. (Germany)
  3. (Greece)
  4. (Germany) and Nuclear and Particle Physics Section, Physics Department, University of Athens, Panepistimioupolis, Ilisia, 157 71 Athens (Greece)
Publication Date:
OSTI Identifier:
20726881
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 32; Journal Issue: 12; Other Information: DOI: 10.1118/1.2126821; (c) 2005 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
61 RADIATION PROTECTION AND DOSIMETRY; ABSORPTION; BRACHYTHERAPY; COMPUTERIZED SIMULATION; DOSE RATES; DOSIMETRY; IRIDIUM 192; MONTE CARLO METHOD; OPTIMIZATION; PROSTATE; RADIATION DOSES; RADIATION SOURCE IMPLANTS; SCATTERING; SHIELDING; YTTERBIUM 169

Citation Formats

Lymperopoulou, G., Papagiannis, P., Sakelliou, L., Milickovic, N., Giannouli, S., Baltas, D., Department of Medical Physics and Engineering, Strahlenklinik, Klinikum Offenbach, 63069 Offenbach, Pi-Medical Ltd., Research and Development Dept., Gennimata 2 Str., 115 24, Ampelokipoi, Athens, and Department of Medical Physics and Engineering, Strahlenklinik, Klinikum Offenbach, 63069 Offenbach. A dosimetric comparison of {sup 169}Yb versus {sup 192}Ir for HDR prostate brachytherapy. United States: N. p., 2005. Web. doi:10.1118/1.2126821.
Lymperopoulou, G., Papagiannis, P., Sakelliou, L., Milickovic, N., Giannouli, S., Baltas, D., Department of Medical Physics and Engineering, Strahlenklinik, Klinikum Offenbach, 63069 Offenbach, Pi-Medical Ltd., Research and Development Dept., Gennimata 2 Str., 115 24, Ampelokipoi, Athens, & Department of Medical Physics and Engineering, Strahlenklinik, Klinikum Offenbach, 63069 Offenbach. A dosimetric comparison of {sup 169}Yb versus {sup 192}Ir for HDR prostate brachytherapy. United States. doi:10.1118/1.2126821.
Lymperopoulou, G., Papagiannis, P., Sakelliou, L., Milickovic, N., Giannouli, S., Baltas, D., Department of Medical Physics and Engineering, Strahlenklinik, Klinikum Offenbach, 63069 Offenbach, Pi-Medical Ltd., Research and Development Dept., Gennimata 2 Str., 115 24, Ampelokipoi, Athens, and Department of Medical Physics and Engineering, Strahlenklinik, Klinikum Offenbach, 63069 Offenbach. Thu . "A dosimetric comparison of {sup 169}Yb versus {sup 192}Ir for HDR prostate brachytherapy". United States. doi:10.1118/1.2126821.
@article{osti_20726881,
title = {A dosimetric comparison of {sup 169}Yb versus {sup 192}Ir for HDR prostate brachytherapy},
author = {Lymperopoulou, G. and Papagiannis, P. and Sakelliou, L. and Milickovic, N. and Giannouli, S. and Baltas, D. and Department of Medical Physics and Engineering, Strahlenklinik, Klinikum Offenbach, 63069 Offenbach and Pi-Medical Ltd., Research and Development Dept., Gennimata 2 Str., 115 24, Ampelokipoi, Athens and Department of Medical Physics and Engineering, Strahlenklinik, Klinikum Offenbach, 63069 Offenbach},
abstractNote = {For the purpose of evaluating the use of {sup 169}Yb for prostate High Dose Rate brachytherapy (HDR), a hypothetical {sup 169}Yb source is assumed with the exact same design of the new microSelectron source replacing the {sup 192}Ir active core by pure {sup 169}Yb metal. Monte Carlo simulation is employed for the full dosimetric characterization of both sources and results are compared following the AAPM TG-43 dosimetric formalism. Monte Carlo calculated dosimetry results are incorporated in a commercially available treatment planning system (SWIFT{sup TM}), which features an inverse treatment planning option based on a multiobjective dose optimization engine. The quality of prostate HDR brachytherapy using the real {sup 192}Ir and hypothetical {sup 169}Yb source is compared in a comprehensive analysis of different prostate implants in terms of the multiobjective dose optimization solutions as well as treatment quality indices such as Dose Volume Histograms (DVH) and the Conformal Index (COIN). Given that scattering overcompensates for absorption in intermediate photon energies and distances in the range of interest to prostate HDR brachytherapy, {sup 169}Yb proves at least equivalent to {sup 192}Ir irrespective of prostate volume. This has to be evaluated in view of the shielding requirements for the {sup 169}Yb energies that are minimal relative to that for {sup 192}Ir.},
doi = {10.1118/1.2126821},
journal = {Medical Physics},
number = 12,
volume = 32,
place = {United States},
year = {Thu Dec 15 00:00:00 EST 2005},
month = {Thu Dec 15 00:00:00 EST 2005}
}
  • Monte Carlo simulation dosimetry is used to compare {sup 169}Yb to {sup 192}Ir for breast high dose rate (HDR) brachytherapy applications using multiple catheter implants. Results for bare point sources show that while {sup 169}Yb delivers a greater dose rate per unit air kerma strength at the radial distance range of interest to brachytherapy in homogeneous water phantoms, it suffers a greater dose rate deficit in missing scatter conditions relative to {sup 192}Ir. As a result of these two opposing factors, in the scatter conditions defined by the presence of the lung and the finite patient dimensions in breast brachytherapymore » the dose distributions calculated in a patient equivalent mathematical phantom by Monte Carlo simulations for the same implant of either {sup 169}Yb or {sup 192}Ir commercially available sources are found comparable. Dose volume histogram results support that {sup 169}Yb could be at least as effective as {sup 192}Ir delivering the same dose to the lung and slightly reduced dose to the breast skin. The current treatment planning systems' approach of employing dosimetry data precalculated in a homogeneous water phantom of given shape and dimensions, however, is shown to notably overestimate the delivered dose distribution for {sup 169}Yb. Especially at the skin and the lung, the treatment planning system dose overestimation is on the order of 15%-30%. These findings do not undermine the potential of {sup 169}Yb HDR sources for breast brachytherapy relative to the most commonly used {sup 192}Ir HDR sources. They imply, however, that there could be a need for the amendment of dose calculation algorithms employed in clinical treatment planning of particular brachytherapy applications, especially for intermediate photon energy sources such as {sup 169}Yb.« less
  • {sup 169}Yb has received a renewed focus lately as an alternative to {sup 192}Ir sources for high dose rate (HDR) brachytherapy. Following the results of a recent work by our group which proved {sup 169}Yb to be a good candidate for HDR prostate brachytherapy, this work seeks to quantify the radiation shielding requirements for {sup 169}Yb HDR brachytherapy applications in comparison to the corresponding requirements for the current {sup 192}Ir HDR brachytherapy standard. Monte Carlo simulation (MC) is used to obtain {sup 169}Yb and {sup 192}Ir broad beam transmission data through lead and concrete. Results are fitted to an analyticalmore » equation which can be used to readily calculate the barrier thickness required to achieve a given dose rate reduction. Shielding requirements for a HDR brachytherapy treatment room facility are presented as a function of distance, occupancy, dose limit, and facility workload, using analytical calculations for both {sup 169}Yb and {sup 192}Ir HDR sources. The barrier thickness required for {sup 169}Yb is lower than that for {sup 192}Ir by a factor of 4-5 for lead and 1.5-2 for concrete. Regarding {sup 169}Yb HDR brachytherapy applications, the lead shielding requirements do not exceed 15 mm, even in highly conservative case scenarios. This allows for the construction of a lead door in most cases, thus avoiding the construction of a space consuming, specially designed maze. The effects of source structure, attenuation by the patient, and scatter conditions within an actual treatment room on the above-noted findings are also discussed using corresponding MC simulation results.« less
  • Purpose: A novel tungsten alloy shielded, MRI-compatible, direction modulated brachytherapy (DMBT) concept tandem applicator, which enables unprecedented intensity modulation, was used to evaluate treatment plan quality improvement over a conventional tandem. The utility of the 192-Ir and 169-Yb HDR sources, for use with the DMBT applicator, was evaluated. Methods: The total diameter of the DMBT tandem applicator is 6.0 mm, which consists of 5.4-mm diameter tungsten alloy and 0.3 mm thick plastic sheath. The tandem has 6 symmetric peripheral 1.3-mm diameter grooves for the source to travel. MCNPX v.2.6 was used to simulate the 192-Ir and 169-Yb sources inside themore » DMBT applicator. First, TG-43 source parameters were evaluated. Second, 3D dose matrix with 1 mm3 resolution were imported into an in-house-coded inverse optimization treatment planning program to obtain optimal plans for 19 clinical cases. All plans were compared with the standard tandem and ring plans. Prescription dose was 15.0 Gy. All plans were normalized to receive the same HRCTV D90. Results: Generally, the DMBT tandem (and ring) plans were better than the conventional tandem and ring plans for 192-Ir and 169-Yb HDR sources. The mean data of D2cc for bladder, rectum, and sigmoid were 11.65±2.30 Gy, 7.47±3.05 Gy, and 9.84±2.48 Gy for Ir-192 DMBT tandem, respectively. These data for Yb-169 were 11.67±2.26 Gy, 7.44±3.02 Gy, and 9.83±2.38 Gy, respectively. The HR-CTV D98 and V100 were 16.37±1.86 Gy and 97.37 ± 1.92 Gy for Ir-192 DMBT, respectively. The corresponding values for Yb-169 were 16.43±1.86 Gy, and 97.51 ± 1.91 Gy. Plans with the 169-Yb source generally produced more favorable results where V100 increased by 13.65% while D2cc across all OARs reduced by 0.54% compared with the 192-Ir plans. Conclusion: For the DMBT tandem applicator, 169-Yb source seems to produce more directional beams resulting in increased intensity modulation capacity, thus resulting in more conformal plans.« less
  • Underlying characteristics in brachytherapy dosimetry parameters for medical radionuclides {sup 137}Cs, {sup 125}I, {sup 192}Ir, {sup 103}Pd, and {sup 169}Yb were examined using Monte Carlo methods. Sources were modeled as unencapsulated point or line sources in liquid water to negate variations due to materials and construction. Importance of phantom size, mode of radiation transport physics--i.e., photon transport only or coupled photon:electron transport, phantom material, volume averaging, and Monte Carlo tally type were studied. For noninfinite media, g(r) was found to degrade as r approached R, the phantom radius. MCNP5 results were in agreement with those published using GEANT4. Brachytherapy dosimetrymore » parameters calculated using coupled photon:electron radiation transport simulations did not differ significantly from those using photon transport only. Dose distributions from low-energy photon-emitting radionuclides {sup 125}I and {sup 103}Pd were sensitive to phantom material by upto a factor of 1.4 and 2.0, respectively, between tissue-equivalent materials and water at r=9 cm. In comparison, high-energy photons from {sup 137}Cs, {sup 192}Ir, and {sup 169}Yb demonstrated {+-}5% differences in dose distributions between water and tissue substitutes at r=20 cm. Similarly, volume-averaging effects were found to be more significant for low-energy radionuclides. When modeling line sources with L{<=}0.5 cm, the two-dimensional anisotropy function was largely within {+-}0.5% of unity for {sup 137}Cs, {sup 125}I, and {sup 192}Ir. However, an energy and geometry effect was noted for {sup 103}Pd and {sup 169}Yb, with {sub Pd-103}F(0.5,0 deg.)=1.05 and {sub Yb-169}F(0.5,0 deg.)=0.98 for L=0.5 cm. Simulations of monoenergetic photons for L=0.5 cm produced energy-dependent variations in F(r,{theta}) having a maximum value at 10 keV, minimum at 50 keV, and {approx}1.0 for higher-energy photons up to 750 keV. Both the F6 cell heating and track-length estimators were employed to determine brachytherapy dosimetry parameters. F6 was found to be necessary for g(r), while both tallies provided equivalent results for F(r,{theta})« less
  • This study presents the results of EGSnrc Monte Carlo calculations of the dose distribution surrounding a high dose rate {sup 169}Yb brachytherapy source and 14 high dose rate and pulsed dose rate {sup 192}Ir brachytherapy sources. Energy-weighted spectra of emitted photons, a full set of TG-43 dosimetry parameters, along-away dose tables, and a description of the materials and geometry used for each source are provided. In addition to this, separate tallies are made of the dose contributed from primary, single-scattered, and multiply-scattered photons. Separation of dose in this manner allows one to use convolution/superposition methods to calculate the dose surroundingmore » a brachytherapy source accounting for a non-homogeneous medium. The effect of phantom size on TG-43 dosimetry parameters and scattered dose is also investigated for the {sup 192}Ir microSelectron v2 HDR source. This paper describes the calculation methods and presents the dose rate constants calculated for each source with the full set of dosimetry data being available online at the Carleton Laboratory for Radiotherapy Physics brachytherapy database (http://www.physics.carleton.ca/clrp/seed lowbar database/).« less