Let's abandon geometry factors other than that of a point source in brachytherapy dosimetry

Meli, Jerome A.

doi:10.1118/1.1496099

Cited by 8 publications

(6 citation statements)

References 9 publications

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“…II B͒. 24 However, the ''exact'' geometry factor will also be used in the discussion of the TG-43 dosimetric parameters dependence and variation. Table II summarizes the MC calculated dose rate constant, ⌳, of the three 60 Co HDR sources as well as a bare 60 Co point source.…”

Section: B Tg-43 Formalism Dosimetry Resultsmentioning

confidence: 99%

“…Therefore, the point or line source approximations 7 are commonly used in extracting the TG-43 dosimetric parameters. Recently, Meli 24 has proposed the exclusive use of point source approximated geometry factors to eliminate the possibility of erroneous dose calculations resulting from a use of one geometry factor in a treatment planning system and another in published TG-43 parameters and ensure that Eq. ͑1͒ is used in a self-consistent manner with regard to geometry factor calculation.…”

Section: B Monte Carlo Calculationsmentioning

confidence: 99%

“…24,25 On the other hand, the use of the line source approximation permits more accurate interpolation of tabulated results for elongated source designs. 26 For the unique source configurations discussed herein we followed Meli 24 and used the point source approximated geometry factors ͓i.e., G(r,)ϭG(r)ϭ1/r 2 ] in extracting TG-43 results that will be tabulated in a grid appropriate to facilitate interpolations. The ''exact'' geometry factors were calculated 10 and used only for the purpose of understanding the TG-43 dosimetric parameters dependence and variation.…”

Section: B Monte Carlo Calculationsmentioning

confidence: 99%

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Monte Carlo dosimetry of HDR brachytherapy sources

et al. 2003

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Monte Carlo based dosimetry is presented for three 60Co HDR sources with a unique configuration of two active pellets in contact or spaced 9 and 11 mm apart. Results are presented in Cartesian "away and along" as well as polar coordinates following the AAPM TG-43 dosimetric formalism. Iso-dose rate contours around the sources in Cartesian coordinates reveal that significant differences between the three source designs exist only close to the source centers where dose rate distributions bear the effect of the unique source configurations. Dose rate constants of all three sources are accurately described by an equation of the form: lambda(cGyh(-1)U(-1))=lambda*pointG(1 cm,90 degrees) = 1.094*G(1 cm,90 degrees) where lambdapoint is the dose rate constant of a bare 60Co point source and G(1 cm,90 degrees) is the "exact" source geometry factor as defined by the TG-43. Radial dose and anisotropy function data extracted using the point source approximated geometry factors are tabulated for all three source designs. Finally, the dependence and variation of the above TG-43 parameters are discussed and it is demonstrated that the dosimetric properties of high-energy photon emitters are largely dependent on radionuclide source distribution.

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Section: B Tg-43 Formalism Dosimetry Resultsmentioning

confidence: 99%

Section: B Monte Carlo Calculationsmentioning

confidence: 99%

Section: B Monte Carlo Calculationsmentioning

confidence: 99%

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Monte Carlo dosimetry of HDR brachytherapy sources

et al. 2003

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“…Furthermore, specific dosimetry parameters have garnered considerable interest in the brachytherapy dosimetry community during recent years. [2][3][4][5][6] For example, dosimetry investigators have suggested both adding complexity 2 and simplifying the geometry function, G͑r , ͒, 4 toward improving brachytherapy dosimetry. The AAPM TG-43U1 currently recommends either a line-or point-source approach to approximate all commercially available brachytherapy seeds.…”

Section: Introductionmentioning

confidence: 99%

Approaches to calculating AAPM TG-43 brachytherapy dosimetry parameters for Cs137, I125, Ir192, Pd103, and Yb169 sources

Melhus

Rivard

2006

Med. Phys.

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Underlying characteristics in brachytherapy dosimetry parameters for medical radionuclides 137Cs, 125I, 192Ir, 103Pd, and 169Yb 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 dosimetry 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 125I and 103Pd 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 137Cs, 192Ir, and 169Yb 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 < or = 0.5 cm, the two-dimensional anisotropy function was largely within +/- 0.5% of unity for 137Cs, 125I, and 192Ir. However, an energy and geometry effect was noted for 103Pd and 169Yb, with Pd-103F(0.5,0 degrees)=l.05 and yb-169F(0.5,0 degrees)=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 approximately 1.0 for higher-energy photons up to 750 keV. Both the F6 cell heating and *F4 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).

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“…Since L is primarily used to minimize interpolation errors during treatment planning, it can take on almost any value. 62,80,81 However, realistic dose distributions are usually best-approximated through using realistic L values. In practice, the geometry function is used by dosimetry investigators to determine other parameters such as g͑r͒ and F͑r , ͒.…”

Section: Vc Geometry Functionmentioning

confidence: 99%

A dosimetric uncertainty analysis for photon‐emitting brachytherapy sources: Report of AAPM Task Group No. 138 and GEC‐ESTRO

et al. 2011

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This report addresses uncertainties pertaining to brachytherapy single-source dosimetry preceding clinical use. The International Organization for Standardization ͑ISO͒ Guide to the Expression of Uncertainty in Measurement ͑GUM͒ and the National Institute of Standards and Technology ͑NIST͒ Technical Note 1297 are taken as reference standards for uncertainty formalism. Uncertainties in using detectors to measure or utilizing Monte Carlo methods to estimate brachytherapy dose distributions are provided with discussion of the components intrinsic to the overall dosimetric assessment. Uncertainties provided are based on published observations and cited when available. The uncertainty propagation from the primary calibration standard through transfer to the clinic for air-kerma strength is covered first. Uncertainties in each of the brachytherapy dosimetry parameters of the TG-43 formalism are then explored, ending with transfer to the clinic and recommended approaches. Dosimetric uncertainties during treatment delivery are considered briefly but are not included in the detailed analysis. For low-and high-energy brachytherapy sources of low dose rate and high dose rate, a combined dosimetric uncertainty Ͻ5% ͑k =1͒ is estimated, which is consistent with prior literature estimates. Recommendations are provided for clinical medical physicists, dosimetry investigators, and source and treatment planning system manufacturers. These recommendations include the use of the GUM and NIST reports, a requirement of constancy of manufacturer source design, dosimetry investigator guidelines, provision of the lowest uncertainty for patient treatment dosimetry, and the establishment of an action level based on dosimetric uncertainty. These recommendations reflect the guidance of the American Association of Physicists in Medicine ͑AAPM͒ and the Groupe Européen de Curiethérapie-European Society for Therapeutic Radiology and Oncology ͑GEC-ESTRO͒ for their members and may also be used as guidance to manufacturers and regulatory agencies in developing good manufacturing practices for sources used in routine clinical treatments.

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Let's abandon geometry factors other than that of a point source in brachytherapy dosimetry

Abstract: Articles you may be interested inComment on "Let's abandon geometry factors other than that of a point source in brachytherapy dosimetry" [Med Limitations of the point and line source approximations for the determination of geometry factors around brachytherapy sources Med.

Cited by 8 publications

References 9 publications

Monte Carlo dosimetry of HDR brachytherapy sources

Monte Carlo dosimetry of HDR brachytherapy sources

Approaches to calculating AAPM TG-43 brachytherapy dosimetry parameters for Cs137, I125, Ir192, Pd103, and Yb169 sources

A dosimetric uncertainty analysis for photon‐emitting brachytherapy sources: Report of AAPM Task Group No. 138 and GEC‐ESTRO

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