ESTRO 2020 Abstract Book

S72 ESTRO 2020

2019, Abstract GS4-02: Regional Lymph Node Irradiation in Early Stage Breast Cancer: An EBCTCG Meta-Analysis of 13,000 Women in 14 Trials, In: Proceedings of the 2018 San Antonio Breast Cancer Symposium: AACR; Cancer Res; 79(4 Suppl). 3) Thorsen, L.B, Offersen, B.V, Dano, H et al, 2016, DBCG-IMN: A Population-Based Cohort Study on the Effect of Internal Mammary Node Irradiation in Early Node- Positive Breast Cancer. J Clin Oncol; 34 (4): 314- 4) Poortmans, P.M, Collette, S, Kirkove, C et al for the EORTC Radiation Oncology and Breast Cancer Groups, 2015, Internal Mammary and Medial Supraclavicular Irradiation in Breast Cancer, N Engl J Med; 373: 317-27. 5) Whelan, T.J, Olivotto, I.A, Parulekar, W.R et al for the MA.20 Study Investigators, 2015, Regional Nodal Irradiation in Early- Stage Breast Cancer , N Engl J Med; 373: 307-16.

Symposium: Radiotherapy: it´s all about the heart

SP-0153 Challenges in treating IMC: An RTT perspective N. Roberts 1 , S. Wickers 2 , D. Ledsom 3 1 leeds Cancer Centre, Radiotherapy, Leeds, United Kingdom ; 2 university College Hopsital, Radiotherapy, London, United Kingdom ; 3 clatterbridge Cancer Centre, Radiotherapy, Liverpool, United Kingdom Abstract text Background: In 2016 the UK consensus guidelines for post- operative breast cancer radiotherapy (RT) were published (1). A consensus was reached on treatment of the internal mammary nodal chain (IMC) based on the most up to date evidence available. The strength of the recommendation varies when considering whether to treat different 'at risk' patient populations within the early breast cancer cohort, hence the word ‘consider' is used in relation to patients with high and low nodal disease burden. Evidence: If outcome measures of all the recent RCTs are combined for ≈11,000 women with median FU of 9.1 years then statistically significant outcomes are reached for: any recurrence, breast cancer specific mortality and overall survival (2). The lack of clarity in consensus reflects the current evidence base with patient disease characteristics under investigation differing somewhat between these studies, but the majority of patients randomised had low volume nodal disease (pN1-3) (3)(4)(5). Absolute mortality benefit was greatest in patients with a higher nodal burden (N4+). Key to this evidence update is the data that shows the more recent RT techniques are far better at sparing organs at risk (OAR) and achieving superior target volume coverage. This is reflected in non-breast cancer mortality which shows no significant difference between patients having IMC and non-IMC RT, a reversal from the older studies that attributed a higher death rate to IMC treatments to excess heart and lung doses (2). The landmark studies into IMC RT have evoked new consideration of treatment for patients where this anatomical region has previously been omitted from the target volume in UK practice. Developing an IMC technique: Traditional RT technique delivery for patients in this disease cohort would include tangential fields to the breast/chest wall with a direct anterior field to the level 4 nodes (SCF). Including the IMC into the target volume poses additional challenges such as; how and what to delineate, how to meet dose constraints for OARs and the potential for increased low dose bath when employing advanced techniques such as VMAT. Given the differences in referring population & radiotherapy planning and delivery equipment, the development and implementation of IMC RT has taken different paths for many cancer centres across the UK. The Leeds Cancer Centre (LCC), University College Hospital London (UCLH) and Clatterbridge Cancer Centre (CCC) represent a diverse referring population and mix of radiotherapy planning and delivery solutions. All have experienced challenges in the development of IMC RT in breast cancer since the consensus guidelines were published. Challenges not only in developing the technique but also in selecting the patient groups that will benefit most whilst ensuring additional resource requirements are used appropriately across the health service. Figure 1 highlights key areas of development that each centre has tackled in implementing IMC RT. At each centre the RTT has been pivotal in this development and case studies from these centres help to illustrate how these challenges have been met. References: (1) Royal College of Radiologists, Faculty of Clinical Oncology on behalf of the core group, 2016, Postoperative radiotherapy for breast cancer: UK consensus statements, retrieved from: https://www.rcr.ac.uk/system/files/publication/field_p ublication_files/bfco2016_breast-consensus- guidelines.pdf (2) Dodwell, D, Taylor, C, McGale, P et al,

SP-0154 Effect of breath-hold in left-sided whole breast irradiation M. Mast 1 , J. Pekelharing 2 , M. Heijenbrok 2 , D. Klaveren Van 3 , L. Kempen Van - Harteveld 1 , A. Petoukhova 1 , A. Verbeek - De Kanter 1 , J. Schreur 4 , H. Struikmans 1 1 haaglanden Medical Centre, Radiation Therapy, Leidschendam, The Netherlands ; 2 haaglanden Medical Centre, Radiology, Leidschendam, The Netherlands ; 3 leiden University Medical Center, Medical Statistics, Leiden, The Netherlands ; 4 haaglanden Medical Centre, Cardiology, Leidschendam, The Netherlands Abstract text Several studies found that radiotherapy for left-sided breast cancer is associated with an increased risk of Coronary Artery Disease (CAD). It appeared that this increased risk is proportional to the mean dose to the heart. Therefore the heart dose should be as low as reasonably achievable when treating left-sided breast cancer patients with whole breast irradiation (WBI). Nowadays, better heart sparing is feasible making use of a breath-hold technique. This technique is easily applied into daily practice and substantially reduces the dose in the heart and the Left Anterior Descending coronary artery (LAD). However, it remains unclear whether this reduction of heart dose results in a lower risk of cardiovascular disease. Therefore, we conducted a prospective longitudinal study to determine whether the use of a breath-hold technique in left-sided breast cancer radiation therapy treatment is associated with less increase of the CAC scores. In this prospective longitudinal study, we compared Coronary Artery Calcium (CAC) scores determined before the start of whole breast irradiation with those determined approximately 7 years afterwards. Methods and materials Initially, we included 109 consecutive patients in this prospective study, all diagnosed with either DCIS or breast cancer. Changes in CAC scores were analysed in 87 breast cancer patients who were able to and agreed to undergo a follow-up CAC CT scan. Three groups were compared: 18 patients receiving right-sided radiotherapy (R-), 14