ESTRO 2024 - Abstract Book

S5958

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

anatomical changes of the breast contour up to 5 mm. However, one hybrid technique could be improved with respect to maximum dose. This study led to an ongoing national initiative to gain insight into the differences in planning approaches, potentially achieving a uniform RT planning approach for breast-cancer treatments.

Keywords: robustness

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Ranking OAR priority in breast VMAT planning comparing VMAT and 3D-CRT related second cancer risk.

Francesco Moretti 1 , Luigi De Cicco 2 , Luca Marzoli 1 , Rita Lorusso 1 , Elena Petazzi 2 , Rossella Margherita Mancuso 2 , Paolo Imperiale 1 , Annalisa Pepe 1 , Sandra Buttignol 2 , Angelo Giovanni Lanceni 2 , Elisa Della Bosca 2 , Daniela Corletto 1 , Lorenzo Bianchi 1 , Barbara Bortolato 2 1 ASST Valle Olona, Division of Medical Physics, Busto Arsizio (VA), Italy. 2 ASST Valle Olona, Division of Radiotherapy, Busto Arsizio (VA), Italy

Purpose/Objective:

The Volumetric Arc Therapy (VMAT) technique in adjuvant breast radiotherapy compared to the 3D-CRT technique increases the low diffuse doses. We attempted to estimate the rise in the risk of secondary cancers in healthy organs. We aimed to determine whether this increased risk is justified considering the improved dose conformity to the target and the significant high dose sparing of nearby healthy organs, as commonly reported in the literature. We also tried to establish a rank of priority for the OARs (Organs at Risk) for VMAT dose optimization in planning.

At our center, introducing the breast VMAT, we mainly treated right breasts, so we retrospectively reviewed VMAT and 3D-CRT right breast plans.

Material/Methods:

We examined adjuvant breast radiation treatment plans of patients with right breast cancer treated at our center between September 2022 and June 2023. Sixty radiation plans were analyzed: twenty-five 3D-CRT plans with sequential surgical bed boost, 40.05Gy/15fx to the whole breast and 10Gy/4fx for sequential overdose, and thirty-five VMAT technique plans targeting the whole breast with a simultaneous boost to the surgical bed with 40.05Gy/15fx and 48 Gy/15fx.

All the plans ensured an optimal target coverage and also all the OARs respected dose limits recommended in literature.

First of all, we calculated the Conformation Number (CN) to estimate the dose conformity on target [1].