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

Abstract

PurposeTo analyze the impact of heterogeneity-corrected dose calculation on dosimetric quality parameters in gynecological 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 methodsCalculations 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 V20Gyαβ3 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.ResultsCalculations 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.ConclusionsLower 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.

Advanced Collapsed cone Engine dose calculations in tissue media for COMS eye plaques loaded with I‐125 seeds

“…As shown by Lesperance et al, using a less water equivalent material for the tumor results in larger differences in dose to the tumor compared to the water‐based scenario. When prescribing dose to the tumor apex this will also change the dose received in all other parts of the eye, demonstrating the importance of accurate material compositions for low‐energy brachytherapy, a detail that is not nearly as critical for high‐energy treatments …”

“…When prescribing dose to the tumor apex this will also change the dose received in all other parts of the eye, demonstrating the importance of accurate material compositions for lowenergy brachytherapy, a detail that is not nearly as critical for high-energy treatments. 9,[39][40][41][42] Transitioning from the traditional TG-43 dose reporting scheme (augmented with corrections for the plaque materials) to a dose to medium reporting scheme is expected to result in more accurate knowledge of doses to various structures in the eye. However, understanding the underlying factors that cause the changes in dose compared to water-based planning will be important to appreciate the clinical implications of implementing model-based dose calculations.…”

Patient's specific integration of OAR doses (D2 cc) from EBRT and 3D image‐guided brachytherapy for cervical cancer

“…The uncertainties of TG 43 dose calculations have been validated through a model‐based dose calculation algorithm that accounts for tissue and applicator heterogeneity 52. The uncertainties of OAR D2 cc in HDR BT plans for cervical cancer have been reported as on average 1%~3% for plastic tandem‐and‐ring (T&R) applicators calculated using a Grid‐Based Boltzmann Solver (GBBS) algorithm (Acuros, Varian Medical System, Inc.)53 or by a collapsed‐cone convolution algorithm (ACE, Elekta Ltd., Stockholm, Sweden) 54. This is also true of titanium T&O applicators 26…”

Experimental verification of Advanced Collapsed‐cone Engine for use with a multichannel vaginal cylinder applicator

“…For gynecological cancer treatments, the present clinical situation that assumes all materials are composed of water has the potential to introduce errors in dose calculations . These errors can potentially cause an undesired increase in radiation dose delivered to organs at risk (OARs: rectum, bladder, and sigmoid colon) or reduced dose to the tumor.…”