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      Monte Carlo‐based beam quality and phantom scatter corrections for solid‐state detectors in 60Co and 192Ir brachytherapy dosimetry

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          Abstract

          Beam quality correction, k QQ 0 ( r ) , for solid‐state detectors diamond, LiF, Li 2 B 4 O 7 , Al 2 O 3 , and plastic scintillator are calculated as a function of distance, r, along the transverse axis of the 60 Co and 192 Ir brachytherapy sources using the Monte Carlo‐based EGSnrc code system. This study also includes calculation of detector‐specific phantom scatter correction, k phan ( r ) , for solid phantoms such as PMMA, polystyrene, solid water, virtual water, plastic water, RW1, RW3, A150, and WE210. For 60 Co source, k QQ 0 ( r ) is about unity and distance‐independent for diamond, plastic scintillator, Li 2 B 4 O 7 and LiF detectors. For this source, k QQ 0 ( r ) decreases gradually with r for Al 2 O 3 detector (about 6% smaller than unity at 15 cm). For 192 Ir source, k QQ 0 ( r ) is about unity and distance‐independent for Li 2 B 4 O 7 detector (overall variation is about 1% in the distance range of 1–15 cm). For this source, k QQ 0 ( r ) increases with r for diamond and plastic scintillator (about 6% and 8% larger than unity at 15 cm, respectively). Whereas k QQ 0 ( r ) decreases with r gradually for LiF (about 4% smaller than unity at 15 cm) and steeply for Al 2 O 3 (about 25% smaller than unity at 15 cm). For 60 Co source, solid water, virtual water, RW1, RW3, and WE210 phantoms are water‐equivalent for all the investigated solid‐state detectors. Whereas polystyrene and plastic water phantoms are water‐equivalent for diamond, plastic scintillator, Li 2 B 4 O 7 and LiF detectors, but show distance‐dependent k phan ( r ) values for Al 2 O 3 detector. PMMA phantom is water‐equivalent at all distances for Al 2 O 3 detector, but shows distance‐dependent k phan ( r ) values for remaining detectors. A150 phantom shows distance‐dependent k phan ( r ) values for all the investigated detector materials. For 192 Ir source, solid water, virtual water, RW3, and WE210 phantoms are water‐equivalent for diamond, plastic scintillator, Li 2 B 4 O 7 and LiF detectors, but show distance‐dependent k phan ( r ) values for Al 2 O 3 detector. All other phantoms show distance‐dependent k phan ( r ) values for all the detector materials.

          PACS numbers: 87.10.Rt, 87.53.Bn, 87.53.Jw

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          Most cited references 12

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          Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations.

          Since publication of the American Association of Physicists in Medicine (AAPM) Task Group No. 43 Report in 1995 (TG-43), both the utilization of permanent source implantation and the number of low-energy interstitial brachytherapy source models commercially available have dramatically increased. In addition, the National Institute of Standards and Technology has introduced a new primary standard of air-kerma strength, and the brachytherapy dosimetry literature has grown substantially, documenting both improved dosimetry methodologies and dosimetric characterization of particular source models. In response to these advances, the AAPM Low-energy Interstitial Brachytherapy Dosimetry subcommittee (LIBD) herein presents an update of the TG-43 protocol for calculation of dose-rate distributions around photon-emitting brachytherapy sources. The updated protocol (TG-43U1) includes (a) a revised definition of air-kerma strength; (b) elimination of apparent activity for specification of source strength; (c) elimination of the anisotropy constant in favor of the distance-dependent one-dimensional anisotropy function; (d) guidance on extrapolating tabulated TG-43 parameters to longer and shorter distances; and (e) correction for minor inconsistencies and omissions in the original protocol and its implementation. Among the corrections are consistent guidelines for use of point- and line-source geometry functions. In addition, this report recommends a unified approach to comparing reference dose distributions derived from different investigators to develop a single critically evaluated consensus dataset as well as guidelines for performing and describing future theoretical and experimental single-source dosimetry studies. Finally, the report includes consensus datasets, in the form of dose-rate constants, radial dose functions, and one-dimensional (1D) and two-dimensional (2D) anisotropy functions, for all low-energy brachytherapy source models that met the AAPM dosimetric prerequisites [Med. Phys. 25, 2269 (1998)] as of July 15, 2001. These include the following 125I sources: Amersham Health models 6702 and 6711, Best Medical model 2301, North American Scientific Inc. (NASI) model MED3631-A/M, Bebig/Theragenics model I25.S06, and the Imagyn Medical Technologies Inc. isostar model IS-12501. The 103Pd sources included are the Theragenics Corporation model 200 and NASI model MED3633. The AAPM recommends that the revised dose-calculation protocol and revised source-specific dose-rate distributions be adopted by all end users for clinical treatment planning of low energy brachytherapy interstitial sources. Depending upon the dose-calculation protocol and parameters currently used by individual physicists, adoption of this protocol may result in changes to patient dose calculations. These changes should be carefully evaluated and reviewed with the radiation oncologist preceding implementation of the current protocol.
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            Dosimetry of interstitial brachytherapy sources: Recommendations of the AAPM Radiation Therapy Committee Task Group No. 43

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              Monte Carlo-aided dosimetry of a new high dose-rate brachytherapy source.

              In this article we introduce a new high-intensity 192Ir source design for use in a recently reengineered microSelectron-HDR remote afterloading device for high dose-rate (HDR) brachytherapy. The maximum rigid length and outer diameter of the new source are reduced to 4.95 and 0.90 mm, respectively, compared to 5.50 and 1.10 mm for the previous source design introduced in 1991. In addition, a smaller diameter and more flexible steel cable are used, allowing the source cable to negotiate smaller diameter catheters or more tortuously curved catheters. Using Monte Carlo photon transport simulation, the complete two-dimensional (2-D) dose-rate distribution is calculated over the 0.1-7 cm distance range and are presented both as conventional 2-D Cartesian lookup tables and in the formalism recommended by the American Association of Physicists in Medicine Task Group 43 (TG-43) Report. The dose distribution of this source is very similar to that of its predecessor, except near the source tip and in the shadow of the cable assembly, where differences of 5%-8% are apparent. The accuracy of various methods for extrapolating beyond the tubulated anisotropy functions to short distances is evaluated. It is demonstrated that linear extrapolation from the anisotropy functions defined by TG-43 accurately (+/- 2%) estimates dose rate at short and long distances lying outside the radial distance range of the original measured data from which the anisotropy and radial dose functions were derived. In contrast, the algorithm used on the vendor's planning system results in large calculation errors at distances less than 5 mm.
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                Author and article information

                Contributors
                b.subwu@gmail.com
                Journal
                J Appl Clin Med Phys
                J Appl Clin Med Phys
                10.1002/(ISSN)1526-9914
                ACM2
                Journal of Applied Clinical Medical Physics
                John Wiley and Sons Inc. (Hoboken )
                1526-9914
                08 November 2014
                November 2014
                : 15
                : 6 ( doiID: 10.1002/acm2.2014.15.issue-6 )
                : 295-305
                Affiliations
                [ 1 ] Radiological Physics & Advisory Division Health, Safety & Environment Group, Bhabha Atomic Research Centre Mumbai 400 094 Maharashtra India
                Author notes
                [* ] a Corresponding author: Mishra Subhalaxmi, Radiological Physics & Advisory Division, Health, Safety & Environment Group, Bhabha Atomic Research Centre, Mumbai – 400 094, Maharastra, India; phone: (91) 22–25598654; fax: (91) 22–25519209; email: b.subwu@ 123456gmail.com

                Article
                ACM20295
                10.1120/jacmp.v15i6.4907
                5711110
                25493516
                © 2014 The Authors.

                This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                Page count
                Figures: 10, Tables: 4, References: 16, Pages: 11, Words: 4442
                Product
                Categories
                Radiation Measurements
                Radiation Measurements
                Custom metadata
                2.0
                acm20295
                November 2014
                Converter:WILEY_ML3GV2_TO_NLMPMC version:5.2.5 mode:remove_FC converted:16.11.2017

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