ESTRO 2024 - Abstract Book

S5942

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

overlap lengths. For CSI VMAT planning, employing the auto feathering algorithm and ensuring field overlap lengths surpass 5 cm are recommended to enhance plan resilience.

Keywords: Plan complexity, VMAT, aperture shape controller

532

Digital Poster

Looking for a criterion to select the patients benefiting of a VMAT technique for breast adjuvant RT

Luigi De Cicco 1 , Francesco Moretti 2 , Rita Lorusso 2 , Luca Marzoli 2 , Elena Petazzi 1 , Rossella Margherita Mancuso 1 , Barbara Bortolato 1 1 ASST Valle Olona, Division of Radiotherapy, Busto Arsizio (VA), Italy. 2 ASST Valle Olona, Division of Medical Physics, Busto Arsizio (VA), Italy

Purpose/Objective:

Considering the possible advantages on the reduction of high doses to the ipsilateral lung compared to the 3D-CRT technique, but also the risk of second tumors induced by the low diffuse doses typical of the volumetric arc technique (VMAT) in adjuvant radiotherapy treatment of the breast, we tried to identify a criterion for identify patients who would benefit most from this new technique regarding high doses to the ipsilateral lung.

At our center, in the initial phase, we mainly treated patients with right breast cancer, so our study only covered this patient setting.

Material/Methods:

We reviewed the radiotherapy plans of the female patients treated on right breast from September 2022 to June 2023 at our center. Sixty radiation plans were evaluated: 35 VMAT technique plans and 25 3D-CRT ones. In the VMAT group the whole breast planned dose was 40.05 Gy, with a simultaneous boost to the surgical bed up to 48 Gy, in 15 fractions. In the 3D-CRT group, the whole breast dose planned was 40.05 Gy in 15 fractions, with sequential surgical bed boost of 10 Gy (50.05 Gy totally) in 4 fractions. The comparison was carried out on the two groups of treatment plans to highlight the dosimetric and isodose conformation differences concerning the reference structures. Therefore, Conformal Index (COIN) values were calculated to compare the isodose conformation to the target and nearby OAR (ipsilateral lung); for both group the average DVH of each OARs was assessed to evaluate technique-dependent dosimetric differences. For every plan we collected the maximum thickness of ipsilateral lung (MTIL) included within the lateral and medial borders of the target, and we related it with V20Gy using the Pearson correlation coefficient by the scipy library in Python [1].