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Dosimetric Advantage of MBDCA-ACE Algorithm (TG-186) Over TG-43 Dose Formalism in HDR Brachytherapy of Accelerated Partial Breast Irradiation (APBI) Using Strut Adjusted Volume Implant (SAVI) Applicator
D Jacob*, N Petersen , L Romak , H Chen , A Sarkar , K Yang , F Mourtada , Christiana Care Hospital, Newark, DE
Presentations
SU-I-GPD-T-32 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To quantify the effect of MBDCA-ACE algorithm in the determination of dose to skin and chest wall for APBI cases, where the HDR brachytherapy applicator is placed very close to the skin/chest wall.
Methods: Two sets of 10 HDR APBI cohorts each, for short skin distances(2-8mm) and chest wall distances (0-4mm) from the lumpectomy cavity, treated with the SAVI device were selected from our extensive HDR database of the past seven years. The original treatment plans calculated with TG-43 dose formalism, using the department CT-based volume optimization and clinical standards were recalculated using the MBDCA-ACE (TG-186) algorithm. The PTV, PTV_Eval, organs at risk as well as the external boundary were contoured on each data set along with significant inhomogeneity like air and high density applicator components. The patient tissue was modeled as homogenous liquid water. D0.1cm³ D1.0cm³ and D2.0cm³ for skin and chest wall were extracted from DVHs for TG-43 and MBDCA calculated plans. Mean difference ± 2σ in the above metrics was calculated for both datasets.
Results: The MBDCA-ACE calculated plans showed an average reduction of 4.4±2.6% and 3.3±1.5% for the 2cm³ skin and chest wall doses respectively. For both cohorts the target coverage (V90) was also reduced by an average of 1.1±1.5% and 1.0±1.0% respectively.
Conclusion: This work indicates that by modeling the scatter conditions appropriately as well as accounting for the heterogeneity and the finite boundary of the patient, the MBDCA-ACE has calculated an accurate dose to the dose limiting structures. This information can now be used to improve target coverage knowing that the dose to the organs at risk is not as high as previously calculated using TG-43 dose formalism and possibly offer HDR based APBI to more patients who were initially thought unfit due to proximity of dose limiting structures to the lumpectomy cavity.
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