ESTRO 2022 - Abstract Book

S718

Abstract book

ESTRO 2022

lymph node involvement (HR 2.9; 95%CI 1.2-7.2), recurrence site (chest wall vs. breast; HR 4.6; 95%CI 1.8-11.6) and thermal dose (low vs. high; HR 4.1; 95%CI 1.4-11.5) were associated with LR control. Three-year late grade 2, 3 and 4 toxicity was 63%, 39% and 0% vs. 54%, 19% and 8% for 23x2Gy and 8x4Gy groups, respectively. No grade 5 late toxicity occurred. The 23x2Gy group had a trend for more grade 3-4 late toxicity ( p =0.064, Fig1B). Conclusion Patients with LR recurrent breast cancer treated with 23x2Gy postoperative re-irradiation and HT tended to have better LR control at the cost of higher incidence of grade 3-4 late toxicity compared to patients treated with 8x4Gy.

Fig 1. Kaplan-Meier survival analysis for A) LR control, B) grade 3-4 late toxicity for patients treated with 8x4Gy and 23x2Gy postoperative re-irradiation and HT for LR recurrent breast cancer.

MO-0799 ESTRO breast cancer CTV contouring guideline - does it work on MRI in prone position?

T. Kulms 1 , T. Teichmann 1 , D. Steinhaus-Wittig 2 , A. Wittig 1 , M. Duma 1

1 University Hospital Jena, Department of Radiotherapy and Radiation Oncology, Jena, Germany; 2 University Hospital Düsseldorf, Institute for Diagnostic and Interventional Radiology, Düsseldorf, Germany Purpose or Objective The aim of this study is to assess the suitability of ESTRO (European society for Radiotherapy and Oncology) computed tomography breast contouring guideline for magnetic resonance imaging (MRI) contouring of the whole breast clinical target volume (CTV) in the prone position. Materials and Methods 56 consecutive left sided breast cancer patients (pts) with breast MRIs were retrospectively chosen for this study. The MRI was performed for diagnostic purposes during the course of the disease, before surgery. On the MRI, the CTV breast was contoured according to the ESTRO CTV guideline (MRI_ESTRO_CTV) in RayStation (V.8, RaySearch Laboratories, Stockholm, Sweden). Further, the glandular tissue only was contoured as well. The delineation was performed by the same observer (TK) and was reviewed by both, a specialized breast cancer radiologist and a breast cancer radiation oncologist. Patients were divided into groups by age (<60 years old, ≥ 60 y.o.), body mass index (BMI: <25; ≥ 25), breast size (<1006cm ³ and ≥ 1006cm ³ ) and therapeutic approach (neoadjuvant systemic therapy (NACT); no NACT). We report median with range and/or average±standard deviations. A value of P<0.05 was considered to be statistically significant. Results 27 pts had a BMI <25, 29 pts a BMI ≥ 25; 30 pts were ≥ 60 y.o., 26 pts <60 y.o.; 28 pts had NACT, 28 had no NACT before the MRI. The MRI_ESTRO_CTV volume was 1006cm 3 (280-2175cm ³ ) and the glandular breast tissue volume was 161cm ³ (60- 552cm ³ ). Patients with BMI <25 and patients with small breasts had a significantly higher portion of glandular breast tissue not included within the MRI_ESTRO_CTV (9.14%±4.78% and 9.48%±4.39% of the contoured glandular tissue were outside the ESTRO CTV, respectively), than patients with BMI ≥ 25 (4.74%±1.83%) and patients with larger breasts (4.45%±1.43%). Figure 1 depicts the typical regions of glandular tissue outside the MRI_ESTRO_CTV (i.e. subcutaneous and extension towards the axilla).