ESTRO 2022 - Abstract Book

S1001

Abstract book

ESTRO 2022

The specific impact of radiotherapy on internal mammary nodes (IMN) remains uncertain. As most IMN recurrences occurs between first and third intercostal space, we analyse the dose received in IMN and its anatomical sections in elective and no intentional IMN irradiation in patients treated with RT for breast cancer. Materials and Methods Prospective study of breast cancer patients treated with breast-conserving surgery and whole breast radiotherapy (WBRT) from July 2020 to September 2021. Fifteen patients were treated only with WBRT (study group: S) and fifteen received elective IMN irradiation (control group: C). All patients were treated with tangential fields optimized using the field in field technique, without specific IMN field. We divided IMN volume in three anatomical sections, upper (1st to 2nd rib), middle (2nd to 4th rib), and lower section (4th to 5th rib). Therapeutic dose (V95) and significant dose with expected therapeutic efficacy (defined as V80) were assessed in total IMN and in every anatomical section. Results Median age was 57 (range: 42 to 78) years. Phenotype of tumors was luminal-A in 17, luminal-B in 8, HER2 in 2, and basal- like in 3. Left breast was affected in 9 patients in S and 9 in C. Central or internal quadrants were affected in 9 patients in S and in 5 in C. Median angulation of the internal tangential was 52° in S and 53° in C (p=0.79). The median percentage of the volume receiving therapeutic dose (V95) in IMN was 17% in the study group and 34% in the control group (p=0.36). V95 by anatomical sections: upper 11% (S) vs. <1% (C) (p=0.01), middle 40% (S) vs. 18% (C) (p=0.21), and lower 39% vs. 44% (p=0.62). The median percentage of volume receiving significant dose (V80) in IMN was 33% in S and 56% in C (p= 0.14); by anatomical sections: upper 5% (S) vs. 0% (C) (p=0.005), middle 71% (S) vs. 36% (C) (p=0.10), and lower 77% vs. 77% (p=1.0). Interquartile range as a measure of dispersion of received doses are presented in Table 1.

Table 1. IQR of the doses received by sections.

Conclusion Even with elective irradiation, most patients did not achieve therapeutic doses in the entire IMN. Specifically, despite intentionality, we only found significant differences in the upper section. Dose received in IMN anatomical section shows a wide variation, probably related to anatomical factors.

PO-1181 The impact of RT on oligorecurrent BC: a retrospective analysis of predictors of clinical outcome

A. Casbarra 1 , S. Frassoni 2 , C. Fodor 3 , A. Ferrari 3 , R. Cambria 4 , F. Colombo 1 , J. Franzetti 1 , C. Giandini 1 , I. Repetti 1 , V. Bagnardi 2 , S. Della Pasqua 5 , M. Colleoni 5 , M.C. Leonardi 6 , B.A. Jereczek-Fossa 1 1 IEO, European Institute of Oncology IRCCS; University of Milan, Division of Radiation Oncology; Department of Oncology and Hematoncology, Milan, Italy; 2 University of Milan-Bicocca, Department of Statistics and Quantitative Methods, Milan, Italy; 3 IEO, European Institute of Oncology IRCCS, Division of Radiation Oncology, Milan, Italy; 4 IEO, European Institute of Oncology IRCCS, Unit of Medical Physics, Milan, Italy; 5 IEO, European Institute of Oncology IRCCS, Division of Medical Senology, Milan, Italy; 6 IEO, European Institute of Oncology IRCCS,, Division of Radiation Oncology, Milan, Italy Purpose or Objective A growing interest has recently raised around the role of radiotherapy (RT) as metastases-directed therapy (MDT) on clinical outcomes of patients affected by oligorecurrent disease. In the current study, we addressed oligometastatic breast cancer