The transition in practice to reduce bolus use in post-mastectomy radiotherapy: A dosimetric study of skin and subcutaneous tissue

Alexandra Guebert; Michael Roumeliotis; Che Hsuan David Wu; Karen Long; Natalie Logie; Tannis Graham; Alison Gourley; Peter Craighead; Michael Sia; Sarah Quirk

doi:10.1016/j.meddos.2023.01.006

The transition in practice to reduce bolus use in post-mastectomy radiotherapy: A dosimetric study of skin and subcutaneous tissue

Med Dosim. 2023;48(2):113-117. doi: 10.1016/j.meddos.2023.01.006. Epub 2023 Mar 10.

Authors

Affiliations

¹ Department of Physics & Astronomy, University of Calgary, Calgary, AB, Canada.
² Department of Physics & Astronomy, University of Calgary, Calgary, AB, Canada; Department of Oncology, University of Calgary, Calgary, AB, Canada; Tom Baker Cancer Centre, Calgary, AB, Canada.
³ Department of Oncology, University of Calgary, Calgary, AB, Canada.
⁴ Tom Baker Cancer Centre, Calgary, AB, Canada.
⁵ Department of Oncology, University of Calgary, Calgary, AB, Canada; Tom Baker Cancer Centre, Calgary, AB, Canada.
⁶ Department of Physics & Astronomy, University of Calgary, Calgary, AB, Canada; Department of Oncology, University of Calgary, Calgary, AB, Canada; Tom Baker Cancer Centre, Calgary, AB, Canada. Electronic address: sarah.quirk@gmail.com.

PMID: 36907800
DOI: 10.1016/j.meddos.2023.01.006

Abstract

To inform clinical practice for women receiving post-mastectomy radiotherapy (PMRT), this study demonstrates the dosimetric impact of removing daily bolus on skin and subcutaneous tissue. Two planning strategies were used: clinical field-based (n = 30) and volume-based planning (n = 10). The clinical field-based plans were created with bolus and recalculated without bolus for comparison. The volume-based plans were created with bolus to ensure a minimum target coverage of the chest wall PTV and recalculated without bolus. In each scenario, the dose to superficial structures, including skin (3 mm and 5 mm) and subcutaneous tissue (a 2 mm layer, 3 mm deep from surface) were reported. Additionally, the difference in the clinically evaluated dosimetry to skin and subcutaneous tissue in volume-based plans were recalculated using Acuros (AXB) and compared to the Anisotropic Analytical Algorithm (AAA) algorithm. For all treatment planning strategies, chest wall coverage (V90%) was maintained. As expected, superficial structures demonstrate significant loss in coverage. The largest difference observed in the most superficial 3 mm where V90% coverage is reduced from a mean (± standard deviation) of 95.1% (± 2.8) to 18.9% (± 5.6) for clinical field-based treatments with and without bolus, respectively. For volume-based planning, the subcutaneous tissue maintains a V90% of 90.5% (± 7.0) compared to the clinical field-based planning coverage of 84.4% (± 8.0). In all skin and subcutaneous tissue, the AAA algorithm underestimates the volume of the 90% isodose. Removing bolus results in minimal dosimetric differences in the chest wall and significantly lower skin dose while dose to the subcutaneous tissue is maintained. Unless the skin has disease involvement, the most superficial 3 mm is not considered part of the target volume. The continued use of the AAA algorithm is supported for the PMRT setting.

Keywords: Bolus; Breast cancer; Post-mastectomy radiation therapy; Skin dose.

MeSH terms

Algorithms
Breast Neoplasms* / radiotherapy
Breast Neoplasms* / surgery
Female
Humans
Mastectomy
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods
Radiotherapy, Intensity-Modulated* / methods
Subcutaneous Tissue