Highlights
- •Significant changes were observed in the breast surface during the course of breast cancer radiotherapy.
- •Because of deformations an additional outer margin is required which is important to consider when using IMRT or VMAT.
- •An additional margin of 8 mm outside the breast surface is required to take account of the changes in the breast surface.
- •The breast deformations were not fully predictable, although a moderate correlation was found with body mass index.
Abstract
Purpose
The aim of this retrospective study was to investigate and quantify the extent of
breast deformation during the course of breast cancer (BC) radiotherapy (RT). The
magnitude of breast deformation determines the additional outer margin needed for
treatment planning to deliver a full dose to the target volume. This is especially
important when using inverse planning techniques.
Methods
A total of 93 BC patients treated with RT and with daily CBCT image guidance were
selected for this study. Patients underwent either only breast-conserving surgery
(BCS) (n = 5), BCS with sentinel node biopsy (n = 57) or BCS with radical axillary node dissection (n = 31). The treatment area included the whole breast and chest wall (54%) or also
the axillary lymph nodes (46%). 3D-registration was conducted between 1731 CBCT images
and the respective planning CT images to assess the difference in breast surface.
Results
The largest maximum breast surface expansion (MBSE) was 15 mm; the average was 2.4 ± 2.1 mm.
In 294 fractions (17%), the MBSE was ≥5 mm. An outer margin of 8 mm would have been
required to cover the whole breast in 95% of the treated fractions. There was a statistically
significant correlation between the MBSE and body mass index (r = 0.38, p = 0.001).
Conclusions
Significant changes in the breast surface occur during the course of BC RT which should
be considered in treatment planning. An additional margin outside the breast surface
of at least 8 mm is required to take into account the anatomical changes occurring
during BC RT.
Keywords
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Article info
Publication history
Published online: August 05, 2019
Accepted:
July 25,
2019
Received in revised form:
July 18,
2019
Received:
March 11,
2019
Identification
Copyright
© 2019 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
