Recent Developments in Basic Brachytherapy Physics

Williamson, Jeffrey F.

doi:10.1007/978-3-662-03107-0_12

Cited by 12 publications

(17 citation statements)

References 103 publications

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“…The path-length attenuation through the source and the capsule wall using the effective-attenuation coefficients for the small source elements takes into account most of the effects. 25 This method is accurate to within 2%-8% for 137 Cs sources but is less accurate at low-and intermediate-photon energies ͑e.g., less than 0.4 MeV͒. 26 The evolution of dosecalculation methods has been discussed and reviewed elsewhere for 137 Cs and low-energy photon-emitting sources.…”

Section: Id Calculations With Encapsulated and Elongated Sourcesmentioning

confidence: 99%

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The evolution of brachytherapy treatment planning

2009

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Brachytherapy is a mature treatment modality that has benefited from technological advances. Treatment planning has advanced from simple lookup tables to complex, computer-based dose-calculation algorithms. The current approach is based on the AAPM TG-43 formalism with recent advances in acquiring single-source dose distributions. However, this formalism has clinically relevant limitations for calculating patient dose. Dose-calculation algorithms are being developed based on Monte Carlo methods, collapsed cone, and solving the linear Boltzmann transport equation. In addition to improved dose-calculation tools, planning systems and brachytherapy treatment planning will account for material heterogeneities, scatter conditions, radiobiology, and image guidance. The AAPM, ESTRO, and other professional societies are working to coordinate clinical integration of these advancements. This Vision 20/20 article provides insight into these endeavors.

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Section: Id Calculations With Encapsulated and Elongated Sourcesmentioning

confidence: 99%

“…Comparison of192 Ir g͑r͒ values calculated for a given spherical water phantom radius R compared to R = 50 cm, which is assumed to provide full scatter conditions. Data include curves for R = 5,10,15,20,25,30,35,40, and 45 cm. Reproduced from Fig.…”

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confidence: 99%

The evolution of brachytherapy treatment planning

2009

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“…Finally, it is clear that neither choice of geometry factor reduces the variation in the angular dose profile data as effectively as for other source types. 22,35 This is due to the nearly complete selfshielding of the distal radioactive sphere near the source tips, a phenomenon which, by definition, is not modeled by the geometry factor. The Electronic Edition also contains a doserate table ͑Table AIII͒ using Cartesian ''away and along'' coordinates to aid in performing quality assurance checks and other types of manual calculations.…”

Section: B Estimation Of Dosimetric Parameters For Clinical Usementioning

confidence: 99%

Dosimetric characteristics of the DRAXIMAGE model LS‐1 I‐125 interstitial brachytherapy source design: A Monte Carlo investigation

Williamson

2002

Medical Physics

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(Received 5 June 2001; accepted for publication 26 December 2001; published 19 March 2002) We have used Monte Carlo photon transport simulations to evaluate dosimetric characteristics of a new 125I seed, the DRAXIMAGE BrachySeed (model LS-1) source for interstitial brachytherapy and to calculate the dosimetric parameters recommended by the AAPM Task Group 43 (TG-43). To eliminate thick end welds, preformed closed-ended Ti shells are welded together near the transverse plane. The radioactivity is localized near the seed ends in order to maximize isotropy at typical prescription distances. Transmission radiography reveals that its internal components can move by as much as 200 microm under the influence of gravitational forces affecting the dose-rate constant and relative dose distribution by as much as 5% and 10%, respectively. However, the clinical dose distribution can be well represented by a weighted average of dose distributions corresponding to three different orientation-dependent internal geometry configurations. This average dose distribution agrees closely (within 1% at 1 cm) with that derived from the geometry specified by the vendor model (seed components uniformly spaced), from which the recommended relative dosimetry parameters were derived. An average dose-rate constant of 0.935 cGy h(-1) U(-1) is recommended for clinical application and values of 0.919, 0.963, and 0.920 for vertical orientation, horizontal orientation, and the vendor specified geometries, respectively. The NIST wide-angle free-air chamber realization of the air-kerma strength primary standard, SKN99, was explicitly simulated. We show that the output of Ag characteristic x rays is about half that of the model 6711 source resulting in a relative dose distribution between that of the model 6711 source and pure 125I x-ray emitters. Finally, it is demonstrated that the TG-43 point-source formalism more accurately estimates solid-angle weighted dose at small distances if one uses a radial dose function data prepared using a point-source, rather than line-source, geometry factor.

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“…[1][2][3][4] Heterogeneities perturb both the primary and scatter components of the radiation field, which results in a dose perturbation that depends on geometry, heterogeneity composition, and radionuclide chosen. Monte Carlo simulation, although highly general and accurate, 1,[5][6][7][8][9][10][11] is at present too CPU intensive to support the volume of dose calculations required by clinical treatment planning given the computing resources currently available for this task. The same is true for the 3D convolution algorithms, [12][13][14] which, while an order of magnitude faster then the Monte Carlo approach, are still too CPU intensive for clinical treatment planning.…”

Section: Introductionmentioning

confidence: 99%

Analytical approach to heterogeneity correction factor calculation for brachytherapy

1998

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In brachytherapy treatment planning, the effects of tissue and applicator heterogeneities are commonly neglected due to lack of accurate, general, and fast three-dimensional (3D) dose-computational algorithms. A novel approach, based on analytical calculation of scattered photon fluxes inside and around a disk-shaped heterogeneity, has been developed for use in the three-dimensional scatter-subtraction algorithm. Specifically, our model predicts the central-ray dose distribution for a collimated photon isotropic source or brachytherapy "minibeam" in the presence of a slab of heterogeneous material. The model accounts for the lateral dimensions, location, composition, density, and thickness of the heterogeneity using precalculated scatter-to-primary ratios (SPRs) for the corresponding homogeneous problem. The model is applicable to the entire brachytherapy energy range (25 to 662 keV) and to a broad range of materials having atomic numbers of 13 to 82, densities of 2.7 g.cm-3 (Al) to 21.45 g.cm-3 (Pt) and thicknesses up to 1 mean free path. For this range of heterogeneous materials, the heterogeneity correction factors (HCFs) vary from 0.09 to 0.75. The model underestimates HCF when multiple scattering prevails and overestimates HCF when absorption dominates. However, the analytic model agrees with Monte Carlo photon transport (MCPT) benchmark calculations within 1.8% to 10% for 125I, 169Yb, 192Ir, and 137Cs for a wide variety of materials, with the exception of Ag. For 125I shielded by Ag, where the mean discrepancy can exceed 25%, the error is due to K-edge characteristic x rays originating within the heterogeneity. The proposed approach provides reductions in CPU time required of 5 x 10(4)-10(5) and 100 in comparison with direct MCPT simulation and 1D numerical integration, respectively. The limitations of model applicability, as determined by the physical properties of heterogeneity material and accuracy required, are also discussed.

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Recent Developments in Basic Brachytherapy Physics

Cited by 12 publications

References 103 publications

The evolution of brachytherapy treatment planning

The evolution of brachytherapy treatment planning

Dosimetric characteristics of the DRAXIMAGE model LS‐1 I‐125 interstitial brachytherapy source design: A Monte Carlo investigation

Analytical approach to heterogeneity correction factor calculation for brachytherapy

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