ESTRO 2021 Abstract Book

S929

ESTRO 2021

After a median follow-up of 4.8 years, only one local recurrence in the chest wall occurred and there was no regional recurrence. The distant metastatic rate was 6%. The long-term recurrence-free survival (RFS) rate was 80% at 5 years. The cause-specific survival rate was 90% at 5 years. The overall survival rate was 55.5% at 5 years. There were 44 (88%) patients with Grade 1 or 2 early toxicity, consisting mainly of dermatitis. There was no Grade 3 or higher acute toxicity registered. Late toxicity was mainly Grade 1 or 2 subcutaneous fibrosis, lymphoedema, and neuropathy except for one patient with Grade 3 fibrosis. Figure legends Figure 1: Overall survival (OS) of elderly patients treated with LR HFRT OS was calculated from time of radiotherapy start to time to time of death. Median follow-up time was 4.8 years. Figure 2: Recurrence-free survival (RFS) and Cancer-specific survival (CSS) of elderly patients treated with LR HFRT Local/ locoregional failure (LRF), distant metastasis (DM) and death events were retrospectively recorded. RFS and CSS were calculated from time of radiotherapy start to time when first event recorded. Median follow-up time was 4.8 years.

Conclusion Extreme LR HFRT is well tolerated with good outcomes and is a good alternative treatment for elderly and frail patients. Our results confirm the efficacy and safety of such a regimen in the setting where LR radiation is needed. Further randomized controlled trials (RCTs) assessing both oncologic outcome and toxicity profile are justified. PO-1116 Evaluation of Nodal CTVs With Deformable Registration After Neoadjuvant Treatment in Breast Cancer M. turna 1 , R. Rzazade 1 , M.D. Canoğlu 1 , E. Küçükmorkoç 1 , N. Küçük 1 , H.B. Çağlar 1 1 Anadolu Medical Center, Radiation Oncology, Kocaeli, Turkey Purpose or Objective Modern radiotherapy techniques require careful delineation of the target. There is no special radiotherapy contouring guideline for patients receiving NACT. In this study, we examined the distribution of pre- chemotherapy clinically positive nodal metastases and explored the coverage rate of the RTOG breast contouring guideline by deformable fusion of PET-CT scan. Materials and Methods We retrospectively evaluated neoadjuvant chemotherapy patients whose pre-treatment PET-CT is available. Patients were simulated in the supine position arms above the head. All PET-CT images were imported into the planning software. The planning computed tomography (CT) and the CT images of PET-CT were first combined with rigid fusion. After that, a deformable registration was performed using regions of interest, defined by involved lymph node regions including pectoralis minor muscle and ribs. All fusions are