ESTRO 2020 Abstract Book

S519 ESTRO 2020

Thirty-one (47%) of 66 patients had additional positive lymph nodes in the ALND (range one to eleven). The chance of a positive ALND increased with increasing number of positive lymph nodes on imaging prior to NAC ( P =0.010), ranging from 25.0% (one positive node) tot 69.0% (three or more positive lymph nodes). Patients with a higher pathologic tumor stage had an increased risk of additional positive lymph nodes in the ALND ( P =0.041). Conclusion The risk of finding additional positive lymph nodes in ALNDs depends on the number of positive lymph nodes before NAC and on the ypT-stage. Randomized trials are currently underway to investigate whether regional radiotherapy may provide locoregional control comparable to ALND in these patients. PO-0974 Helical intensity-modulated radiation therapy for locally advanced breast cancer:a prospective study B. Bataille 1 , F. Le Tinier 1 , R. Bennadji 1 , L. Basson 1 , A. Escande 1 , E. Tresch 2 , F. Crop 3 , F. Darloy 4 , D. Carlier 4 , X. Mirabel 1 , E. Lartigau 1 , D. Pasquier 1 1 Oscar Lambret Center, Radiation therapy, Lille, France ; 2 Oscar Lambret Center, Biostatistics, Lille, France ; 3 Oscar Lambret Center, Medical Physic, Lille, France ; 4 Leonard de Vinci Center, Radiation therapy, Dechy, France Purpose or Objective Intensity-modulated radiation therapy (IMRT) is known to provide better coverage of complex target volumes for adjuvant breast radiotherapy. It provides dosimetric advantages in order to reduce high doses delivered to organ at risk such as heart and lungs. IMRT also improves acute and late toxicity compared to conventional radiotherapy. The objective of this study is to evaluate acute and late toxicities as well as quality of life for patients treated by helical tomotherapy for locally advanced breast cancer. Material and Methods This was a prospective, routine care study, including patients treated by tomotherapy. Prescribed dose to the breast/chest wall/axillary lymph nodes was 50 Gy (25 fractions x 2 Gy) over five weeks (5 irradiations/week) with simultaneous integrated boost (SIB) at surgical bed (PTV- boost) of 60 Gy in 25 fractions (25 fractions x 2.4 Gy) after conservative treatment. The goal of the prescription was that 95% of the volume received 95% of the prescribed dose. The primary endpoint was acute and late toxicities assessed by NCI-CTCAE v4.0 scale. Secondary endpoints were quality of life using QLQ-C30 and QLQBR-23 questionnaires, aesthetic aspect of the breast after breast conserving surgery, survival (assessed by Kaplan Meier method), association between clinical or dosimetric characteristics and toxicity Results 288 patients were included from November 2014 to January 2018. 260 patients (90.3%) underwent lymph node irradiation. The median follow-up was 25 months. 278 patients (96.5%) had acute dermatitis : 172 (59.7%) grade 1, 102 (35.4%) grade 2, and 4 (1.4%) grade 3. 18 patients (6.3%) had grade 2 acute esophagitis. 86 patients (29.9%) had medium-term skin reaction, including 82 grade 1. 18 patients (6.3%) and 17 patients (10.1%) had grade ≥2 breast fibrosis and surgical bed fibrosis respectively (table 1). In multivariate analysis, smoking, D98% of supra-clavicular skin and absence of chemotherapy were associated with medium-term skin toxicity grade ≥2. The aesthetic aspect of the breast after one year was estimated "good or excellent" in 86.7% of cases according to the physician and 84.6% according to the patients. Patient’s quality of life improved over time. It concerned global health status, functional and symptomatic scale. Patients who were treated by chemotherapy before radiotherapy had poorer mean scores at the inclusion time, and most of them were significatively improved at one and six months. Two years

Conclusion HFRT with concomitant boost allows for treatment acceleration and dose escalation in the area of higher risk of relapse. According to the findings from this study, HFRT with concomitant boost appears to be a safe and effective technique, with acceptable toxicity. PO-0973 Axillary lymph node dissection after neoadjuvant chemotherapy for node-positive breast cancer. M. Van Zeeland 1 , P. Westhoff 1 , C. Wauters 2 , P. Bult 3 , A. Werner 4 , N. Laurens 5 , L. Strobbe 6 , H. Meijer 1 1 Radboud University Medical Center, Radiation Oncology, Nijmegen, The Netherlands ; 2 Canisius Wilhelmina Hospital, Pathology, Nijmegen, The Netherlands ; 3 Radboud University Medical Center, Pathology, Nijmegen, The Netherlands ; 4 Radboud University Medical Center, Surgical Oncology, Nijmegen, The Netherlands ; 5 Canisius Wilhelmina Hospital, Medical Oncology, Nijmegen, The Netherlands ; 6 Canisius Wilhelmina Hospital, Surgical Oncology, Nijmegen, The Netherlands Purpose or Objective Following neoadjuvant chemotherapy (NAC) for clinically node-positive breast cancer, axillary lymph node dissection (ALND) is often performed, when the marked node remains positive after NAC. The purpose of this study was to determine the possibility of predicting additional positive lymph nodes in ALNDs and to identify potential risk factors for having additional positive lymph nodes in ALNDs. Material and Methods The selected patients had been diagnosed with invasive breast cancer and lymph node positive disease detected by ultrasound of the axilla and cytologically or histologically confirmed (cT1-4 N1-3 M0). The positive lymph nodes were marked with a radioactive iodine seed or with a radio- opaque marker. Patients with a persistently positive marked lymph node after NAC, undergoing ALND, were analyzed for predictors of additional positive lymph nodes in ALNDs. Results