ESTRO 2020 Abstract book

S568 ESTRO 2020

contouring, was higher in P1 and P2 than in P3 - having P1 and P2 higher values of CI, DSC and Incl.Idx and lower values of MDC. The same analysis was carried out on each nodal level (Table 2). Considering the average on all patients, L4 showed the highest concordance with the corresponding GS both in terms of shape and volume, both in terms of position.

Results Table 1 shows the global results. The use of bra resulted in a significant dose reduction in lung (Dmean and V16Gy reduced by 7% and 11%, respectively), in heart (V10Gy reduced by 9%) and in liver (60% reduction in Dmean). Regardingbreast volume and ptosis grade, the highest benefits were seen in large breasts> 2000 ml and in GIII ptosissubgroup. Reproducibility was excellent, with minorpositioning shifts during treatment. Image 1. No acute skin toxicities > G2 and no differences were observed compared to patients treated without bra.

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Conclusion Substantial differences were observed between the SCCTV and the GSCTV of the 3 representative patients, especially for the one with altered arm set-up (P3). The central levels (L2 and L3) were the most penalized. Overall, the results show a very high variability in lymph nodes contouring, which raises some issues in the era of highly conformal techniques. PO-0980 Preliminar evaluation of a new bra for large or pendular breasts irradiation. F. Castaño 1 , J. Gomez 1 , M. Árquez 1 , J. Acosta 1 , V. Hernandez 2 , A. Camarasa 2 , L. Torres 1 , P. Araguas 1 , M. Arenas 1 1 Hospital Universitari Sant Joan de Reus, Department of Radiation Oncology, Reus, Spain ; 2 Hospital Universitari Sant Joan de Reus, Physics Department, Reus, Spain Purpose or Objective Treating patients with large or pendulous breasts can be problematic. The aim of the present study is to investigate the possible dosimetric benefitof a new bra (Chabner XRT® Radiation Bra CIVCO) for large or pendulouswhole breast irradiation (WBI), as well as assess its impact on reproducibility and toxicity. Material and Methods Prospective study of patients with large or pendulous breast treated with conservative surgery and sentinel node biopsy candidates to WBI. Mammary ptosis classified according to Regnaul scale: GI: mild, GII: moderate and GIII: severe. Two CT studies were carried out in 14 patients, with one study usingthe breast bra. Radiation plans were produced with bra and without bra and the following parameters were compared: Dmeanlungdose (ipsilateral)and V16Gy, Dmeanheartdoseand V10Gy and Dmeanliverdose. Dailyverification of patient positioning was done using ConeBeam CT.Toxicity was evaluated weekly according to RTOG scale. Statistics: difference of means in the cohorts, paired Student's T-test, Pearson's correlation coefficient. Significant probability: p<0.05.

Conclusion Our results show that the use of Chabner XRT® Radiation Bra during WBI for patients with large or pendulous breastsimprovedall the main dosimetric factors evaluated. The treatment reproducibility was excellent and no acute toxicities > G2 were observed. PO-0981 Variability of axillary nodal CTV contouring in breast cancer (PART II – dosimetric impact) M.C. Leonardi 1 , F. Cattani 1 , M. Pepa 1 , R. Luraschi 2 , S. Vigorito 2 , S.G. Gugliandolo 1 , D. Ciardo 1 , R. Orecchia 3 , B.A. Jereczek-Fossa 1 , A. Breast Cancer Study Group 4 1 IEO- European Institute of Oncology IRCCS, Division of Radiotherapy, Milan, Italy ; 2 IEO- European Institute of Oncology IRCCS, Department of Medical Physics, Milan, Italy ; 3 IEO- European Institute of Oncology IRCCS, Scientific Directorate, Milan, Italy ; 4 Associazione Italiana di Radioterapia Oncologica, Airo, Milan, Italy

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