ESTRO 2022 - Abstract Book

S1044

Abstract book

ESTRO 2022

DSI CTV_breast would increase by 0.05 (p<0.05). In contrast the DSI heart would decrease by 0.002 (p<0.05) for every inhaled 100cm ³ . Conclusion The individual anatomy of the patient - such as breast volume or amount of deep inspiration – have an impact on DIR accuracy. DIR of the whole image is not enough for precise volumetry of organs and implicitly dose deformations between FB and DIBH datasets. Performing focused DIR is an option.

PO-1237 Implementation of SAPBI using Cyber-Knife:Dosimetry report and early experiences of a phase II trial

N. Mészáros 1 , V. Smanykó 1 , T. Major 1 , G. Stelczer 2 , L. Jánváry 1 , Z. Takácsi-Nagy 1 , C. Polgár 1

1 National Institute of Oncology, Center of Radiotherapy, Budapest, Hungary; 2 National Institute of Oncology, Center of Radiotheapy, Budapest, Hungary Purpose or Objective To report the implementation, dosimetric results and early experiences of stereotactic accelerated partial breast irradiation (SAPBI) following breast conserving surgery (BCS) for low-risk early stage invasive breast cancer. Materials and Methods Between November 2018 and October 2021, 64 patients with low risk early invasive (St I-II) breast cancer underwent BCS were enrolled in our phase II prospective study. SAPBI was performed with Cyber-Knife (CK) M6 machine, to a total dose of 25 Gy in 4 daily fractions of 6.25 Gy. Respiratory movements were followed with implanted gold markers and Synchrony system. Corrections for patient displacement and respiratory movement during treatment were performed with the robotic arm. Side effects, cosmetic results and dosimetric parameters were assessed. Results At a median follow up to 24 months (range: 1-35) no locoregional or distant metastases was observed. The average volume of the surgical cavity, clinical target volume (CTV) and planning target volume (PTV_EVAL) was 7.7 cm 3 (range: 1.75-27.3 cm 3 ), 54.3 cm 3 (range: 26.2-103.5 cm 3 ) and 74.6 cm 3 (range: 40-135.4 cm 3 ) respectively. The mean value of the PTV/whole breast volume ratio was 0.09 (range: 0.04-0.19). No grade 2 or worst acute and late side-effect was detected. Acute side effects included Grade 1 (G1) erythema occurred in 13 (20.3%) patients, while G1 oedema was observed in 7 (10.9%) cases. G1 pain was reported by 3 (4.6 %) patients. Late side effects included G1 skin toxicity in 2 (3%), G1 and G2 fibrosis in 2 (3%) and 1 (1.5%) patient respectively. G1 pain in 3 (4.7%) cases. Cosmetic outcome was excellent in 41 (64 %) and good in 23 (36 %) patients. Conclusion SAPBI with CK is a reproducible and feasible technique for the delivery of external beam APBI following BCS for the treatment of low-risk, early-stage invasive breast carcinoma. Our early findings are promising, CK-SAPBI delivered with four daily fractions is well tolerated by the patients. I. Ratosa 1 , N. Privsek 2 , N. Dobnikar 1 , E. Matos 2 , A. Gojkovic Horvat 1 , D. Golo 1 , J. Gugic 1 , M. Ivanetic Pantar 1 , M.S. Paulin Kosir 1 , T. Marinko 1 , C. Grasic Kuhar 2 1 Institute of Oncology Ljubljana, Division of Radiation Oncology, Ljubljana, Slovenia; 2 Institute of Oncology Ljubljana, Division of Medical Oncology, Ljubljana, Slovenia Purpose or Objective To evaluate 15-year outcomes for patients with ductal carcinoma in situ (DCIS) of the breast, receiving mastectomy, breast conserving surgery (BCS) alone or with whole breast radiotherapy (BCS+RT). Previously described patient prognostic score and tumour resection margins were also assessed. Materials and Methods The study cohort consisted of all eligible patients with DCIS treated between years 1994 and 2011. Data on type of surgery, tumour resection margins and RT were retrieved retrospectively using medical records. For each patient previously described prognostic score was calculated, considering patient age (>60 years = 0, 40–60 years = 1, <40 years = 2), tumour size (<16 mm = 1, 16–40 mm = 1, >40 mm = 2) and tumour grade (G1 = 0, G2 = 1, G3 = 2). The Kaplan-Meier method was used to calculate estimated survival curves for locoregional recurrence rates (LRR) and invasive relapse-free survival (iRFS) and compared by the log-rank test. Cox’s proportional hazards model was used to assess the effects of covariates on survival. Results Of the 883 patients included in the study, 311 (35.2%) received mastectomy, 265 (30%) received BCS+RT and 307 (34.8%) received BCS. The median age was 56 years old (range, 18–87). Prognostic score calculation was available for 859 patients as follows: 289 (33.6%) scored <2 points and 570 (64.6%) scored ≥ 2 points. Resection margin status was as follows: positive (R1) in 36 (4.1%), close (<2 mm) in 144 (16.3%), ≥ 2 mm in 657 (74.1%), and unknown margin status in 46 (5.2%) patients. At PO-1238 Long-term outcome in patients with ductal carcinoma in situ of the breast