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ISSN: 1689-832X
Journal of Contemporary Brachytherapy
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2/2016
vol. 8
 
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abstract:
Original paper

Impact of heterogeneity-corrected dose calculation using a grid-based Boltzmann solver on breast and cervix cancer brachytherapy

Julia Hofbauer
,
Christian Kirisits
,
Alexandra Resch
,
Yingjie Xu
,
Alina Sturdza
,
Richard Pötter
,
Nicole Nesvacil

J Contemp Brachytherapy 2016; 8, 2: 143–149
Online publish date: 2016/04/19
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Purpose: To analyze the impact of heterogeneity-corrected dose calculation on dosimetric quality parameters in gyne¬cological and breast brachytherapy using Acuros, a grid-based Boltzmann equation solver (GBBS), and to evaluate the shielding effects of different cervix brachytherapy applicators.

Material and methods: Calculations with TG-43 and Acuros were based on computed tomography (CT) retrospectively, for 10 cases of accelerated partial breast irradiation and 9 cervix cancer cases treated with tandem-ring applicators. Phantom CT-scans of different applicators (plastic and titanium) were acquired. For breast cases the V to lung, the D0.1cm³, D1cm³, D2cm³ to rib, the D0.1cm³, D1cm³, D10cm³ to skin, and Dmax for all structures were reported. For cervix cases, the D0.1cm³, D2cm³ to bladder, rectum and sigmoid, and the D50, D90, D98, V100 for the CTVHR were reported. For the phantom study, surrogates for target and organ at risk were created for a similar dose volume histogram (DVH) analysis. Absorbed dose and equivalent dose to 2 Gy fractionation (EQD2) were used for comparison.

Results: Calculations with TG-43 overestimated the dose for all dosimetric indices investigated. For breast, a decrease of ~8% was found for D10cm³ to the skin and 5% for D2cm³ to rib, resulting in a difference ~ –1.5 Gy EQD2 for overall treatment. Smaller effects were found for cervix cases with the plastic applicator, with up to –2% (–0.2 Gy EQD2) per fraction for organs at risk and –0.5% (–0.3 Gy EQD2) per fraction for CTVHR. The shielding effect of the titanium applicator resulted in a decrease of 2% for D2cm³ to the organ at risk versus 0.7% for plastic.

Conclusions: Lower doses were reported when calculating with Acuros compared to TG-43. Differences in dose parameters were larger in breast cases. A lower impact on clinical dose parameters was found for the cervix cases. Applicator material causes systematic shielding effects that can be taken into account.
keywords:

Acuros, breast, brachytherapy, cervix, dose calculation

 
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