ESTRO 2023 - Abstract Book

S1013

Digital Posters

ESTRO 2023

In April 2020, the “Fast Forward” study was published showing the efficacy of an extreme hypofractionated radiotherapy scheme, delivering the total dose of radiation in five sessions. We present the experience in our department with patients treated with this regimen under routine clinical practice conditions, reporting short-term toxicity and efficacy outcomes. Materials and Methods Descriptive observational study of 160 patients diagnosed with breast cancer. From July 2020 to December 2021, we evaluated the results obtained in all patients that were treated with conservative surgery and posteriorly by breast irradiation alone according to the Fast Forward protocol at a total dose of 26 Gy/in five fractions over one week. Patients were women with invasive or ductal in situ carcinoma of the breast and were treated by Breast-conserving surgery with sentinel lymph node biopsy (SLNB) or Axillary dissection (ALND). Concurrent endocrine therapy or trastuzumab were administred. The clinical target volume (CTV) encompassed all palpable breast tissue, excluding the rib cage and pectoralis muscle strain. The planning target volume (PTV) that represents setup error and patient breathing was defined as 5 mm expansion around the CTV, but within the patient's external contour. Patients received 26 Gy in five fractions of 5.2 Gy using the irradiation techniques previously described. A sequential tumour bed radiotherapy boost (10 Gy in five fractions of 2Gy) over lumpectomy cavity was administrated with patient selection based on the discretion of the treating physician. Regarding the follow-up of the patients, clinical examination and acute toxicity were assessed during the treatment, at the completion of treatment, 4 weeks after treatment and subsequently every 6 months for 1 year, using the Common Terminology Criteria for Adverse Events (version 4.0) Results Median of age was 64 years (43-83). 82 patients (51.3 %) have been treated for left, 77 (48.1 %) for right and 1 (0.6 %) for bilateral breast cancer. 66 patients had pT1c (41.3 %), and 71.3 % were ductal infiltrative. Tumours were mainly intermediate grade (41.9 %), hormone-sensitive (81.3 %), with low proliferation index (Ki-67 <20%; 51.9 %), HER2 negative (85 %). Surgical resection margins were mainly negative (99.4 %). A total of 72,5 % and 23.8 % received hormonotherapy and chemotherapy respectively. A minority of patients received an additional tumour boost following WHBI of 10 Gy in five sessions of 2 Gy over a week. The median of PTV volume was 899 cm3 (110-2509 cm3). The early toxicity observed was grade I radio dermatitis in 117 patients (73.1 %). With a median of follow up of 15 months (3.9-28.77) only one patient has presented local relapse treated with mastectomy. Conclusion Extreme hypofractionated scheme on the breast alone, out of a clinical trial, have shown to be feasible, with very low early toxicity. A greater follow-up is necessary to assess long-term toxicity and efficacy. 1 Virgen de la Victoria University Hospital, Radiation Oncology, Malaga, Spain; 2 Virgen de la Victoria University Hospital, Radiation Oncology, Malaga, Spain; 3 Virgen de la Victoria University Hospital, Radiation Oncology , Malaga, Spain Purpose or Objective We hypothesise that partial-breast radiotherapy restricted to the vicinity of the original tumour, in women with favourable early-stage breast cancer, treated with 3D-RT in five sessions, is safe and effective treatment. We present the experience in our department with patients treated with this regimen under routine clinical practice conditions, reporting short-term toxicity and efficacy outcomes. Materials and Methods Women diagnosed with breast cancer, who were aged 45 years or older who had breast-conserving surgery for unifocal invasive ductal adenocarcinoma of any grade. Other inclusion criteria were pathological tumour 3 cm or less (pT1–2), axillary node negative and minimum microscopic margins of 2 mm or more. All the patients have been treated with external radiotherapy, with 3D. During treatment patients positions was verificated using cone-beam CT. A dose of 30 Gy en five non-consecutive daily fractions at 6 Gy/ fraction was prescribed. Results Between January 2017 and December 2021 we treated 228 patients, a median follow-up of 36.4 months (5.9–51.9), a median aged 61 (41-86) years old. The average tumor was 12 mm (2 to 39 mm). The tumor: pT1: 89%, pT2:11%. Phenotype: 88% Luminal. No local or regional recurrence was observed. Early skin reactions: no documented toxicity according Radiation Therapy Oncology Group (RTOG) in 116 (51%), grade I: 104 (46%), grade II: 7 (3%). No late skin toxicity Grade II, III. Conclusion Accelerated partial breast irradiation has developed as alternative radiation techniques for select patients with favourable early-stage breast cancer. These radiation regimens are safe and allow for greater patient convenience (fewer sessions). PO-1268 Five-day accelerated partial breast irradiation with 3D radiotherapy. Experience in our institution A. Calvo Tudela 1 , S. Segado Guillot 1 , M.J. Garcia Anaya 2 , N. Martin Romero 3 , I. Garcia Rios 3

PO-1269 Cardiological monitoring and safety of 5-fraction whole breast irradiation: SAFE-FORWARD study

C. Becherini 1 , C. Bellini 1 , G. Barletta 2 , L. Visani 3 , L. Marrazzo 4 , E. Scoccimarro 1 , C. Cerbai 1 , G. Frosini 1 , A. Peruzzi 1 , I. Bonaparte 1 , B. Bettazzi 1 , V. Lorenzetti 1 , V. Salvestrini 3 , M. Valzano 1 , M. Mangoni 1 , M. Casati 4 , S. Pallotta 4 , I. Meattini 1 , L. Livi 1