Modeling AeroForm tissue expander for postmastectomy radiation therapy.

Elaine Dziemianowicz,Indrin J Chetty,Stephen J Gardner,Correen Fraser,Eleanor M Walker,Anne Reding,Ning Wen,Karen Chin Snyder

doi:10.1002/acm2.12682

Elaine Dziemianowicz, Indrin J Chetty + Show 6 more

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https://doi.org/10.1002/acm2.12682

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Abstract

The AeroForm chest wall tissue expander (TE) is a silicon shell containing a metallic CO2 reservoir, placed surgically after mastectomy. The patient uses a remote control to release compressed CO2 from the reservoir to inflate the expander. AeroForm poses challenges in a radiation therapy setting: The high density of the metallic reservoir causes imaging artifacts on the planning CT, which encumber structure definition and cause misrepresentation of density information, in turn affecting dose calculation. Additionally, convolution‐based dose calculation algorithms may not be well‐suited to calculate dose in and around high‐density materials. In this study, a model of the AeroForm TE was created in Eclipse treatment planning system (TPS). The TPS model was validated by comparing measured to calculated transmission through the AeroForm. Transmission was measured with various geometries using radiochromic film. Dose was calculated with both Varian’s Anisotropic Analytical Algorithm (AAA) and Acuros External Beam (AXB) algorithms. AAA and AXB were compared using dose profile and gamma analyses. While both algorithms modeled direct transmission well, AXB better modeled lateral scatter from the AeroForm TE. Clinical significance was evaluated using clinical data from four patients with AeroForm TEs. The AeroForm TPS model was applied, and RT plans were optimized using AAA, then re‐calculated with AXB. Structures of clinical significance were defined and dose volume histogram analysis was performed. Compared to AXB, AAA overestimates dose in the AeroForm device. Changes in clinically significant regions were patient‐ and plan‐specific. This study proposes a clinical procedure for modeling the AeroForm in a commercial TPS, and discusses the limitations of dose calculation in and around the device. An understanding of dose calculation accuracy in the vicinity of the AeroForm is critical for assessing individual plan quality, appropriateness of different planning techniques and dose calculation algorithms, and even the decision to use the AeroForm in a postmastectomy radiation therapy setting.

Highlights

For breast cancer patients with greater than four positive lymph nodes, positive or close margins, or a tumor greater than 5 cm, the National Comprehensive Cancer Network guidelines recommend postmastectomy radiation therapy (PMRT)
Using optimal geometry and imaging technique, the AeroForm CO2 reservoir alone can be exquisitely imaged without a metal artifact reduction (MAR) reconstruction
This study describes a technique to model the AeroForm tissue expander (TE) in a commercially available treatment planning system (TPS)

Summary

Introduction

For breast cancer patients with greater than four positive lymph nodes, positive or close margins, or a tumor greater than 5 cm, the National Comprehensive Cancer Network guidelines recommend postmastectomy radiation therapy (PMRT). There is no consensus on the optimal method and timing of postmastectomy breast reconstruction for patients receiving PMRT.[1,2,3] One common technique is the two‐stage breast reconstruction. In this method, a tissue expander (TE) is placed at the time of mastectomy. The TE is gradually expanded to the desired size, and PMRT is delivered after expansion is complete. The TE is exchanged for a permanent implant.[4,5,6]

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