ESTRO 2020 Abstract book

S96 ESTRO 2020

PD-0177 Interfraction heart motion during Deep Inspiration Breath Hold (DIBH) radiotherapy measured by CBCT. S. Benkhaled 1 , D. Van Gestel 1 , A. Desmet 1 , D. Rodriguez 2 , Y. Jourani 2 , A. De Caluwé 1 1 Institut Jules Bordet-Université Libre de Bruxelles, Department of Radiation-Oncology, Bruxelles, Belgium ; 2 Institut Jules Bordet-Université Libre de Bruxelles, Department of Medical-Physics, Bruxelles, Belgium Purpose or Objective Deep Inspiration Breath Hold (DIBH) decreases the radiation dose to the heart, an important goal in left breast radiotherapy (RT). This study aimed to quantify the inter-fractional heart motion (3D) of DIBH during RT as measured by daily CBCT (Cone-Beam-Computed- Tomography), the hypothesis of the study being that patients might perform breath hold differently during their RT course. DIBH might improve during the course with the heart moving further away from the chest wall as the patient gains experience in performing DIBH, as well as it can deteriorate due to fatigue or lack of patient cooperation and motivation. This study is one of the first to look at 3D movement of the heart using daily CBCT acquired in DIBH at every treatment fraction. Material and Methods Fifteen consecutive DIBH treatments performed by tracking the respiratory cycles using a surface-guided- radiotherapy system were retrospectively analyzed. Target and organs at risk were delineated as per ESTRO guidelines. The prescribed dose was 40 Gy in 15 fractions. At the pre-RT consultation, we recommended our patients to practice apnea in order to increase the DIBH efficiency and endurance. After each delivered fraction, RT- technologists gave a feedback to the patient on their DIBH. Daily CBCT was acquired and retrospectively 3- dimensionally co-registered by the same radiation oncologist to the DIBH planning-CT. Heart position on the DIBH planning-CT was considered as the reference position. Two different offline co-registrations were performed: 1) on the thoracic wall (X bones ,Y bones ,Z bones ) and 2) on the heart (X heart ,Y heart ,Z heart ) to calculate heart displacement relative to the thoracic wall. The total 3D heart motion was calculated as [δ x = (√[X bones -X heart ] 2 + [Y bones -Y heart ] 2 + [Z bones -Z heart ] 2 )]. Results Two hundred twenty-five CBCTs from 15 patients were analyzed. High intra and inter-individual heterogeneity was observed. The mean additional displacement of the heart relative to the planning-CT during the DIBH course was: X= -0.82 mm (standard deviation (SD) 6.5 mm); Y= +0.15 mm (SD 3.8 mm) and Z= -0.47 mm (SD 6.18 mm). The total (3D) mean motion was: δ tot = 0.96 mm (SD 4.8 mm). The displacements did statistically not significantly differ from the reference heart position on the simulation Ct- scan.

Large retrospective population-based studies of early- stage breast cancer (BC) suggest that breast-conserving therapy (BCT) is at least equivalent or even better in terms of BC-specific and overall survival (OS) compared to mastectomy. In this study, we compared BCT consisting of breast conserving surgery (BCS) and radiotherapy to mastectomy-only in stage I-IIA BC. Material and Methods The study cohort consisted of all stage I-IIA (T1/2N0 or T0/1N1) BC patients diagnosed in 2013 and treated with BCT or mastectomy-only, achieving clear margins, and with a known surrogate definition of intrinsic subtype of BC (Luminal A-like, Luminal B-like HER2‐negative, Luminal B-like HER2‐positive, HER2‐positive and triple negative BC). Differences between patients treated with BCT and those treated with mastectomy were compared using the chi-squared test, 5-year overall (OS) and disease-free survival (DFS) were estimated using Kaplan-Meier method and multivariate Cox proportional hazards models were conducted to estimate hazard ratios (HRs) for OS and DFS. Results Of the 568 patients included in the study, 421 (74.1%) received BCT and 147 (25.9%) mastectomy. Compared to BCT, mastectomy group had more patients younger than 45 years (17.7% vs. 8.8%, p=0.003), higher Charlson comorbidity index score (CCI) (p<0.001), more patients had multicentric BC (65.3% vs. 26.8%, p<0.001) and more patients had axillary lymph node dissection (20.4% vs. 12.3%, p<0.001). However, no significant differences were observed between patients treated with BCT vs. those with mastectomy in the distribution of overall stage, intrinsic subtype, receipt of endocrine therapy, chemotherapy, or targeted (anti-HER2) therapy. Median follow-up was 55.2 months. Two (0.4%), 1 (0.2%) and 14 (2.5%) patients experienced local, regional and distant relapse, respectively, and 24 (4.2%) patients died. Kaplan-Meier estimated 5-year DFS was 95.4% in BCT (95% confidence intervals (CI) 93.4–97.4) and 88.7% (95% CI 83.2–94.2) in mastectomy group (p=0.014). Estimated 5-year OS was 96.9% (95% CI 95.3–98.5) in BCT group compared to 91.8% (95% CI 87.1–96.5) in mastectomy group (p=0.024). In adjusted analysis accounting for age, CCI, multicentricity, overall stage, intrinsic subtype, type of primary local treatment and receipt of chemotherapy, only younger age was significantly associated with improved 5-year OS. However, in adjusted analysis accounting for the same confounding factors, receipt of BCT had a significantly positive effect on DFS compared with mastectomy (HR 0.42; 95% CI 0.19–0.91; p=0.027).

Conclusion Our study demonstrated superior 5-year DFS in patients stage I-IIA BC treated with BCT compared to mastectomy. Improved outcome was observed regardless of age, overall stage, comorbidity, intrinsic subtype, multicentricity and receipt of chemotherapy. Our data adds to previous research showing a benefit of BCT when compared to mastectomy in patients suitable for both treatments.

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