liu.seSearch for publications in DiVA
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Monte Carlo-aided dosimetry of the symmetra model I25.S06 125I, interstitial brachytherapy seed
Linköping University, Department of Medicine and Care, Radiation Physics. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Medicine and Care, Radiation Physics. Linköping University, Faculty of Health Sciences.ORCID iD: 0000-0003-0209-498X
Radiation Oncology Center, Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, USA.
2000 (English)In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 27, no 5, 1076-1085 p.Article in journal (Refereed) Published
Abstract [en]

A dosimetric study of a new 125I seed for permanent prostate implant, the Symmetra 125I Seed model I25.S06, has been undertaken utilizing Monte Carlo photon transport calculations. All dosimetric quantities recommended by the AAPM Task Group 43 (TG-43) report have been calculated. Quantities determined are dose rate constant, radial dose function, anisotropy function, anisotropy factor, and anisotropy constant. The recently (January 1999) revised NIST (National Institute of Standards and Technology) 125I standard for air kerma strength calibration was taken into account as well as updated interaction cross-section data. Calculations were done for the competing model 6702 source for the purpose of comparison. The calculated dose-rate constants for the two seeds are 1.010 and 1.016 cGyh−1U−1 for the Symmetra and model 6702 seeds, respectively. The latter value deviates from the value, 1.039 cGyh−1U−1, recommended in the TG-43 report. The calculated radial dose function for the Symmetra new seed is more penetrating than that of the model 6711 seed (by 20% at 5 cm distance) but agrees closely (within statistical errors) with that of the model 6702 seed up to distances of 10 cm. The anisotropy function for the seed is also close to that for the 6702 seed with a tendency of somewhat more pronounced anisotropy (lower values at small angles from the longitudinal axis). Compared to the model 6711 seed, the Symmetra new seed is more isotropic. The anisotropy constants (the anisotropy function averaged with respect to angle and distance) for the three seed models are within 2%.

Place, publisher, year, edition, pages
2000. Vol. 27, no 5, 1076-1085 p.
Keyword [en]
dosimetry, radiation therapy, Monte Carlo methods, radioisotopes, iodine, calibration, dosimetry, permanent brachytherapy implant, 125I, Task Group 43, Monte Carlo simulation
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-26768DOI: 10.1118/1.598990Local ID: 11369OAI: oai:DiVA.org:liu-26768DiVA: diva2:247318
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Dosimetry in brachytherapy: application of the Monte Carlo method to single source dosimetry and use of correlated sampling for accelerated dose calculations
Open this publication in new window or tab >>Dosimetry in brachytherapy: application of the Monte Carlo method to single source dosimetry and use of correlated sampling for accelerated dose calculations
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Three issues related to brachytherapy dosimetry are addressed in this thesis. (1) The prospect of using Compton scattering to measure energy spectra from a high dose-rate (HDR) 192Ir source is discussed and a Compton spectrometer evaluated. Promising results are demonstrated but further fine-tuning is needed to resolve problems with background subtraction. (2) Absorbed doses around an interstitial brachytherapy 125I-source (the Symmetra™ seed) are calculated in the TG-43 formalism using Monte Carlo (MC) techniques. A review of the literature on current measurements and MC simulations indicate systematic differences of 3-6% for the model 6702 seed and points to the need for renewed attention to the dosimetry of low-energy photons and careful estimations of uncertainty. The problems concern among other points: the energy response of LiF dosemeters including LET (Linear Energy Transfer) dependence and the influence of high atomic number doping materials, the atomic compositions of Solid Water and other phantom materials used in MC simulations, the proper MC simulation of the new NIST (National Institute of Standards and Technology) air-kerma strength calibration standard based on the wide-angle free air chamber, and the benchmarking of MC codes. (3) In order to promote development of MC based dose planning, correlated sampling as a means of speeding-up MC calculations is evaluated. In this pilot study, simplified physics is used. Only the photoelectric effect (disregarding the emission of characteristic x-rays) and Compton scattering (Klein-Nishina) are considered. Analogue (ANL) and expected value track-length (ETL) estimations are compared. Efficiency gains (relative to uncorrelated ETL estimations) are calculated for simplified geometries with a point isotropic source and a cylindrical heterogeneity of air, AI and W in a water medium. Efficiency gains of 103 - 104 were obtained for modest perturbations (heterogeneity correction factors HCF [0.8 <HCF < 1.2]). At large perturbations [HCF ≈ 0.4-0.5], in volume elements (voxels) behind the heterogeneity, correlated sampling can be even less efficient than uncorrelated sampling. With correlated ETL estimation, an overall gain in efficiency was, however, achieved and relative standard deviations less than 2% were obtained in 90% of the voxels for an 1251- source and 1-hour computing-time. Uncorrelated ETL estimation was 10-100 times more efficient than uncorrelated ANL estimation. Although promising, correlated sampling should be combined with some other variance reduction technique to reduce the variance everywhere in the volume. Analysis of the uncertainties of estimated efficiency gains shows that the use of the Fisher F distribution to derive their confidence intervals is suspect.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2003. 59 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 790
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-27489 (URN)12143 (Local ID)91-7373-549-3 (ISBN)12143 (Archive number)12143 (OAI)
Public defence
2003-05-27, Berzeliussalen, Hälsouniversitet, Linköping, 09:00 (Swedish)
Opponent
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2012-10-10Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text

Authority records BETA

Hedtjärn, HåkanAlm Carlsson, Gudrun

Search in DiVA

By author/editor
Hedtjärn, HåkanAlm Carlsson, Gudrun
By organisation
Radiation PhysicsFaculty of Health Sciences
In the same journal
Medical physics (Lancaster)
Medical and Health Sciences

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 73 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf