Abstract Book

S694

ESTRO 37

Purpose or Objective Whole breast radiotherapy following breast conserving surgery is a well established standard of care resulting in relative risk reduction for local recurrence of 50% compared to no radiotherapy. However, radiotherapy is associated with long term toxicity including cardiovascular disease and studies have shown a linear dose response of mean heart dose and the risk of a cardiovascular event occurring. Deep inspiration breath hold technique (DIBH) moves the heart away from the radiation field and results in lower mean heart doses. Here we estimated the reduction in cardiovascular risk using DIBH vs standard free breathing (FB) radiotherapy. Material and Methods 35 patients were selected who had both FB and DIBH pre treatment planning scans. Mean heart dose was calculated on each scan. Baseline cardiovascular risk was calculated for each individual patient using the Q-Risk calculator and increased cardiovascular risk from radiation to the heart was calculated. The cardiovascular risk between the FB and DIBH techniques were compared with patients acting as their own control. Results The average reduction in mean heart dose was 46 cGy when comparing FB to DIBH. The mean average absolute risk reduction in cardiovascular disease was 0.34%; relative risk reduction was 3%. The number needed to treat to prevent a cardiovascular event using DIBH technique vs FB was 294 in this cohort. Conclusion In our cohort of patients we estimate DIBH technique in breast radiotherapy compared to standard FB technique results in a 3% relative risk reduction of developing a cardiovascular event. EP-1257 Voluntary Deep Inspiration Breathhold (DIBH) in the Radiotherapy for Breast Cancer I. Gueorguiev 1 , N. Nedev 2 , A. Avramov 3 , N. Velikova 1 , A. Tonev 4 1 Acibadem City Clinic University Cancer Center, Radiation Oncology, Sofia, Bulgaria 2 Acibadem CityClinic University Cancer Center, Radiation Oncology, Sofia, Bulgaria 3 Acibadem City Clinic University Cancer Center, REadiation Oncology, Sofia, Bulgaria 4 Acibadem City Clinic University Cancer Centerf, Radiation Oncology, Sofia, Bulgaria Purpose or Objective The adjuvant radiotherapy to the whole breast or the chest wall is an integral part of the treatment of breast cancer. With left side breast tumours, inevitably a small portion of the lung and the heart gets irradiated when tangential radiotherapy fields are used. The problem is even larger when internal mammary lymph nodes (IMN) have to be included in the radiotherapy area. This study is aimed at evaluating the dosimetric consequences and the potential for sparing of the heart and lung with breathing adapted radiotherapy (BART), using voluntary deep inspiratory breath-hold (DIBH) technique for radiotherapy of left sided breast or chest wall. Material and Methods 95 patients with breast cancer (09.2016 – 09.2017), had planning CT scans in the different distinct respiratory phases, using Varian Real Time Positioning Management System® for monitoring of the respiratory anterior- posterior chest wall excursions. Each patient had two planning CT scans: one during free breathing (FB) and another one with voluntary deep inspiration breath-hold (DIBH). The Planning Target Volume (PTV) in some of the patients included the whole breasts (or the chest wall) only, whereas in other patients the PTV included the breast (or the chest wall) and supraclavicular nodal groups (SCL). For each patient, two radiotherapy plans were prepared using the FB and the DIBH planning scans

Homogeneity-Indices have been calculated as suggested in ICRU 83 and ICRU 62. For 3 adolescent patients (twelve to seventeen years of age) mediastinal CTV and PTV target volumes have been delineated by 5 independent physicians. The gold-standard target-volume contour has been defined by the STAPLE method. Each single PTV has been evaluated in comparison to the gold standard. Results Proton irradiation results in significant lower doses delivered to organ at risk. As well the maximum doses as the mean doses have been decreased while PTV coverage is comparable. For example, the mean heart dose is reduced by 55% using protons. Also doses to the substructures of the heart, the lungs and the mammarial glands are significantly lower for proton radiotherapy. The mean DVH for the coronary vessels reveals significant lower doses by proton RT compared to photon VMAT. The Conformity Index shows better results for the VMAT plan (Mean VMAT 1,09 vs. Proton plan 1,38) and the homogeneity index is better for the proton plan (Mean 0,137 Photons vs. 0,099 Protons).

Conclusion For young patients proton therapy of mediastinal lymphoma reduces doses to organs at risk and opens the possibility to further minimize the possibility of late toxicities and adverse effects such as secondary malignancies and cardiovascular events.

Electronic Poster: Clinical track: Breast

EP-1256 Cardiovascular risk reduction by deep inspiration breath hold technique in breast cancer. B. McCann 1 , R. Stevens 1 , P. Houston 1 1 NHS greater glasgow and clyde, Beatson West of Scotland Cancer Centre, glasgow, United Kingdom