ESTRO meets Asia 2024 - Abstract Book

S81

Interdisciplinary – Breast

ESTRO meets Asia

262

Digital Poster

Hybrid short-arc VMAT for whole breast: A new standard for large volume breasts?

Thomas Hinz-Berg Johansen, Mette Marie Bruun Nielsen

Department of Oncology, Zealand University Hospital, Næstved, Denmark

Purpose/Objective:

Whole breast irradiation of large volume breasts (volume > 700 cc) usually necessitates use of mixed photon energies when using 3DCRT and is often accompanied by excessive high dose outside the breast. Energies often exceed 10 MV, which may result in neutron contamination. Butterfly plans combine VMAT technique with the advantage of short-arc tangential fields in dose sparing of heart and lungs, but are more difficult and time consuming to plan. Hybrid planning combines 3DCRT with butterfly VMAT fields, expanding degrees of freedom for planning, and keeping the robustness of 3DCRT while using only 6 MV beams. Three different planning techniques were investigated on eleven patients with breast cancer being treated with 40 Gy/15 fx. All plans were made in Eclipse (v. 16.1): 1) 3DCRT using tangential fields with support fields of mixed energies. 2) Butterfly plan with four short-arc VMAT fields: two medial and two lateral. 3) Hybrid planning with two primary tangential fields and 6 MV support fields when necessary, contributing 90% of the dose, and two short arc (30-40°) butterfly VMAT fields from the medial and lateral side, respectively. See Figure 1. The hybrid and butterfly plans were restricted to one dose optimization. No skin flash or body extensions were used. Delivery times of each technique were compared for four patients. Robustness tests were performed by calculating plan uncertainty parameters for geometrical shifts of ± 0.5, 1.0, and 1.5 cm in all dimensions. Robustness with respect to breast swelling was investigated by extending the body structure with an increase of 0.5, 1.0, and 1.5 cm, respectively, around the breast and setting the extension to 0 HU. Target coverage (V95% ≥ 98%) and OAR doses according to Danish national constraints were evaluated for all plans. For four patients all plans were measured on the Octavius 4D phantom to test the deliverability of the different techniques. 3D gamma pass rates (global, 3%/3 mm) were calculated using Verisoft. All plans were delivered on a TrueBeam. Material/Methods:

Made with FlippingBook flipbook maker