ESTRO 2021 Abstract Book

S942

ESTRO 2021

(33.50%) and Dmean_LV (40.17%) than SLE plans; lung inferior expansion correlated to lower Dmean_LAD (28.15%) and Dmean_Lt lung (13.06%) than SLE plans (Table 2). There was no correlation between CTV volume and dose reductions to OARs. Linear regression analysis showed that during the inhalation, right movement of 1 mm of heart could reduce Dmean_heart by 0.28 Gy and the Dmean_LV by 0.46 Gy. Conclusion For the adjuvant treatment of left-sided breast cancer, DIBH plans showed significant dose reductions to heart, LV, LAD and the left lung compared with SLE and MLE plans. Dose reductions to heart and left lung significantly correlated with the inferior and anterior expansions of left lung, and the inferior and right movements of heart. PO-1134 MRI and PET response after preoperative radiochemotherapy in HER2+/triple negative breast cancer A. Montero 1 , R. Ciervide 1 , M. Garcia-Aranda 1 , B. Alavarez 2 , X. Chen-Zhao 1 , R. Alonso 1 , M. Lopez 1 , O. Hernando 1 , E. Sanchez 1 , J. Valero 1 , M. Nuñez 1 , M. Izquierdo 1 , K. Rossi 1 , C. Cañadillas 3 , D. Zucca 4 , A. Prado 4 , J. Garcia 4 , P. Garcia 4 , P. Fernandez-Leton 4 , C. Rubio 1 1 HM Hospitales, Radiation Oncology, Madrid, Spain; 2 HMHospitales, Radiation Oncology, Madrid, Spain; 3 HM Hospital, Radiation Oncology, Madrid, Spain; 4 HM Hospitales, Medical Physics, Madrid, Spain Purpose or Objective Complete pathologic response (pCR) is considered to be a subrogate parameter of survival in unfavourable breast cancer subtypes.This ongoing protocol of preoperative radiochemotherapyscheduleseeks to correlate metabolic and radiologic response with rates of pCR in patients with localized triple negative (TN) or HER2- enriched (HER2+) breast cancer Materials and Methods This is a unicentric prospective study that enrolles TN/HER2+ breast cancer patient’s cT2-4cN0-3 to receive concomitant neoadjuvant radiochemotherapy. 18 FDG-PET-CT is used for radiotherapy simulation. Radiotherapy schedule consists of 40.5Gy in 15 fractions of 2.7Gy delivered to WBRT and axillary levels I-IV (AL) with ipsilateral internal mammary chain when indicated and a simultaneous integrated boost of 3.6Gy in 15 fractions on macroscopic and hipermetabolic tumor areas highlighted by PET up to a total dose of 54Gy. Catalyst® SGRT system and kV-CBCT is used for IGRT allowing online inter and intrafraction patient tracking. Radiation is delivered during the first 3 weeks of chemotherapy. Concomitant chemotherapy according to molecular subtype is Pertuzumab-Trastuzumab-Paclitaxel followed by anthracyclines in Her-2 positive patients and CBDCA-Paclitaxel followed by anthracyclines in TN patients (Figure 1). Another 18 FDG-PET and MRI are performed presurgically. Study endpoints are to assessradiological and metabolic response after neoadjuvant chemoradiation. Results From October 2018 to December 2020, 55p have been enrolled. At time of this analysis, 36p (50% TN and 50% HER2+) have finished primary radiochemotherapy and surgery. With a median follow up of 15.7 months, 100% had metabolic(32p total response, 1p major response, 3p did not performed) and radiological response (26p total response, 9p major response, 1p did not performed). The 64% of patients reached pathologic complete responseMiller- PayneG5: (23p),22% G4 (8p) and 14% G3 (5p). The negative predictive value (NPV) of 18 FDG-PET and MRI were 71.8% and 88.4% respectively. We performed a comparative analysis with Chi-Square test and according to 18 FDG-PET-SUV value, we found a weak trend to signification between 18 FDG-PET-SUV-value <7.2 and pathological response (p: 0.08). Conclusion The challenge in the management of breast cancer resides not only in the most optimal therapies but also in the use of the bests imaging tests. While 18 FDG-PET is a really useful image tool in the treatment planning process of this preoperative radiochemotherapy approach, the presurgical MRI shows a better NPV to estimate pathologic response PO-1135 Ultra-hypofractionated whole breast radiotherapy with integrated boost for early breast cancer A. Montero 1 , R. Ciervide 1 , M. Garcia-Aranda 1 , B. Alvarez 1 , A. Prado 2 , X. Chen-Zhao 1 , R. Alonso 1 , M. Lopez 1 , E. Sanchez 1 , O. Hernando 1 , J. Valero 1 , M. Nuñez 1 , M. Izquierdo 1 , K. Rossi 1 , C. Cañadillas 1 , P. Fernandez-Leton 2 , C. Rubio 1 1 HM Hospitales, Radiation Oncology, Madrid, Spain; 2 HM Hospitales, Medical Physics, Madrid, Spain Purpose or Objective Whole breast irradiation (WBI) after breast conserving surgery (BCS) is indicated to improve loco-regional control and survival. Former studies showed that addition of tumor bed boost in all age groups significantly improved local control although no apparent impact on overall survival but with an increased risk of worse cosmetic outcome. Although hypofractioned regimens in 3 weeks are considered the standard, recent studies have shown the non- inferiority of a treatment regimen of 5 fractions in one-week in both locoregional control and toxicity profile. We present our preliminary results of acute toxicity of a ultra-hypofractionated 5 fractions in one-week WBI schedule with simultaneous integrated boost (SIB) in early breast cancer. Materials and Methods