Abstract Book

S296

ESTRO 37

mean=5.23Gy, SD=1.94Gy vs. FB mean=10.88Gy, SD=3.95Gy p<0.000) when treated using DIBH over FB. Amplitude depths were not correlated with dose reductions, however, a DIBH depth proved superior to free breathing regardless if it was high, or low amplitude. Conclusion: DIBH treatment resulted in dose sparing for the heart and LADCA compared to FB treatment. This occurred simultaneously without increased dose to the combined or ipsi-lateral lung. Amplitude depths were not correlated with dose reduction hence cannot be used as indicators to achieve increased dose sparing effect. Further research and long term follow up is required to evaluate the clinical effect DIBH has in reducing long term cardiac/pulmonary complications and increasing patients’ overall mortality. SP-0562 Follow-up heart dose reduction. Where do we stand? M. Mast 1 , H. Struikmans 2 1 Haaglanden Medical Centre Location Westeinde Hospi, Radiation therapy DepartmentPostbus 411- 2260 LeidschendamROOM A2.003, Den Haag, The Netherlands 2 Haaglanden Medical Centre Antoniushove, Radiation therapy Department, Leidschendam, The Netherlands Abstract text Worldwide the highest rates of breast cancer are found in Western Europe [1]. Ferley et al. published the European figures, 464.000 new cases were diagnosed in 2012 [2]. Radiation therapy is often part of the treatment after breast conserving surgery, as became apparent from the EBCTCG data that the local recurrences were decreased by 2/3 in the group of patients receiving radiotherapy [3]. In the past decade it became apparent that after several years serious side effects might occur. Associations of RIHD with (mean) cardiac dose levels were described. In 2013 Darby et al. reported that rates of major coronary events increased with 7.4% per Gray and were proportional to the mean dose to the heart. It was shown that radiation induced heart diseases (RIHD) occur earlier than previously anticipated (< 5 years). Furthermore, they could not find a threshold dose [4]. This was confirmed in a study of van den Boogaard et al. Also it appeared that the left ventricular dose was a better predictor for risk on acute coronary events (ACE) [5] Apart from this, interactions with specific cytotoxic agents may lead to more heart damage. Rehammar et al. found the largest increases risk of heart disease in women who also received anthracycline-containing chemotherapy [6]. Finally, several studies investigate the risk factors for heart disease as well. Wethal et al. found that the irradiated arteries are characterized by widespread atherosclerotic lesions in lymphoma survivors [7]. The amount of Coronary Artery Calcium (CAC), is a reliable predictor of ACE in the general population [8,9]. And recently Roos et al. found that high pre-treatment CAC appears to be associated with ACE in breast cancer patients treated with postoperative radiotherapy [10]. Apart from the increasing awareness of these side effects, methods were found to decrease the dose in the heart and heart vessels. Using a breath-hold technique in patients with left-sided breast cancer is one of them [11]. In our department we found a less pronounced increase of CT-based CAC scores when using a breath- hold technique [12]. In this era of highly sophisticated technical improvements individualization of the cancer treatment will bring us a step forward aiming at a longer survival and a better quality of life. 1. https://breast.cancerresearch/breast-cancer-facts- and-figures/ 2. Ferley et al. European Journal of Cancer 2013;49:1374 3. EBCTC Group. Lancet 2005;365:1687 4. Darby et al. N Engl J Med 2013;368:987 5. Van den Boogaard et al. J Clin Oncol 2017;35:1171

Symposium: Focus on site - BREAST

SP-0561 The Clinical Impact of DIBH For Breast Radiotherapy G. Lawler 1 , M. Leech 2 1 Beacon Hospital, Clinical Trials Research Unit- Radiotherapy Department Level -1, Dublin 18, Ireland 2 Trinity College Dublin, Radiation Therapy, Dublin, Ireland Abstract text Aim: To assess if deep inspiration breath-hold (DIBH) treatment for left breast radiotherapy patients, resulted in dose sparing for organs-at-risk compared to free breathing (FB) treatment. Consequently, to evaluate if breath-hold amplitude depths could be correlated with observed dose reductions. Background Historically, left breast cancer patients treated with radiotherapy experienced improved cancer survival however, mortality rates did not decrease. This was directly related to long term treatment side effects, mainly chronic cardiac (e.g. coronary artery disease, ischaemia, myocardial infarction) and less so, pulmonary complications (e.g. pneumonitis), induced from radiotherapy treatment. Today, left breast cancer patients continue to be at an increased risk of cardiac complications induced from treatment, particularly compared to right breast patients. DIBH could potentially reduce dose to organs-at-risk without compromising target dose, hence potentially reducing complication incidence and improving patients’ quality of life and overall survival. Materials & Methods FB and DIBH CT planning scans obtained using Varian RPM Gating software for n=28 left breast/left chest wall +/- left supraclavicular patients, treated between January 2008-December 2013 were retrospectively re-contoured and re-planned. Organs-at-risk included the lungs, left lung, heart and left anterior descending coronary artery (LADCA). 6MV field-in-field tangential technique was used and occasionally low weighted 15MV beams also, to achieve improved dose coverage and homogeneity. Mono- isocentric technique was used for all supraclavicular patients, n=4. Cardiac shielding, without target dose compromise, was performed on all 56 plans. Maximum plan dose was kept within 1% agreement between FB and DIBH plans for comparative purposes. Varian Eclipse software was used to plan all patients and Anisotropic Analytical Algorithm (AAA) used for dose calculations. Statistical analysis of treatment plans was then performed. Results: No dose benefits or disadvantages were established for the combined lungs or ipsi-lateral lung using DIBH over FB technique. However, the smaller volumes of heart receiving large doses, D10%- D50% heart volume inclusive, received significant dose reductions using DIBH ranging from 27%-12.7% respectively. Maximum heart dose, Dmax was relatively reduced by 34.5% (Mean=41.81Gy, SD=3.963Gy FB vs Mean=27.39Gy, SD=12.393Gy DIBH, p<0.000) while mean heart dose, Dmean achieved a 32.6% reduction (Mean=1.817Gy, SD=0.627Gy FB vs Mean=1.224Gy, SD=0.344Gy DIBH, p<0.000). The heart was completely removed from the treatment field using DIBH in 28.6%, n=8 participants. The LADCA also experienced significant reductions in dose received by all volumes examined, D10%- D100% inclusive, with dose reductions recorded ranging from 56.9%-27.4% respectively. The maximum LADCA dose, Dmax was reduced by 47.8% (DIBH mean=15.56Gy, SD=10.62Gy vs. FB mean=29.82Gy, SD=10.05Gy, p<0.000) and Mean LADCA Dose, Dmean by 52% (DIBH