Abstract
To investigate the near-surface doses and target coverage in modulated arc radiotherapy
(RT) of the breast or chest wall in two treatment planning systems (TPS) in the presence
of soft tissue deformations. This retrospective study consisted of 10 breast cancer
patients with axillary lymph node inclusion. For each case, five RT plans were created:
(1) tangential 3D conformal field-in-field (FinF) technique; (2) 200° to 240° arcs
with optimization bolus (OB) in Eclipse (EB); (3) 243° to 250° arcs with an 8-mm OB
in Monaco (MB); (4) 243° to 250° arcs with automatic skin flash tool (ASF) in Monaco
TPS (MA); (5) 243° to 250° arcs with both ASF and OB in Monaco (MAB). Soft tissue
deformation was simulated by editing CT-images with 4-, 8-, and 12-mm swelling and
recalculating the dose. The increasing swelling from 0 to 12 mm caused the coverage
(V95%) in clinical target volume to decrease from 96% ± 2% to 90% ± 6% for the FinF
plans. For volumetric-modulated arc therapy (VMAT), the coverage decreased from 99%
± 1% to 92% ± 4% in the EB plans, and from 97% ± 1% to 68% ± 8%, 85% ± 6%, and 86%
± 5% for MA, MB, and MAB, respectively. The mean dose in the surface extending from
0 to 3 mm from the skin decreased on average 5%, 17%, 20%, 15%, and 8% in FinF, EB,
MA, MB, and MAB, respectively. In the Monaco plans, the use of an OB(+ASF) provided
better target coverage and lower dose maxima despite of tissue swelling than the ASF
alone. With modulated arc therapy, we recommend the use of an OB instead of or in
addition to the ASF. The use of 8 mm OB with VMAT plans is robust to account deformations
extending outside up to 8mm. If soft tissue deformation is larger than 8 mm, the need
for replanning should be evaluated.
Keywords
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Article info
Publication history
Published online: September 26, 2020
Accepted:
September 8,
2020
Received in revised form:
August 28,
2020
Received:
May 20,
2020
Identification
Copyright
© 2020 American Association of Medical Dosimetrists. Published by Elsevier Inc. All rights reserved.
