ESTRO 2020 Abstract Book

S497 ESTRO 2020

doses to the heart and lungs are increased. This study compared conformal radiotherapy using wide tangents (WT) versus volumetric arc therapy (VMAT) with and without a breath hold technique. Material and Methods Datasets from 15 patients were used to compare WT to treat the breast/chest wall and IMC with VMAT in free breathing (FB) and voluntary deep inspiratory breath hold (vDIBH). Each technique was tested for right-sided RT and vDIBH only was used for left-sided RT). ESTRO guidelines were used for outlining left and right IMC and level 3 and 4 lymph nodes for all cases. We compared target volume coverage and OAR doses for each technique using the Mann-Whitney test, and p-values of <0.05 were statistically significant. Results Constraints for breast planning target volume (PTV) coverage (V95%>95%) were met and were similar for each technique. Coverage of the IMC PTV was better with VMAT than WT (>98% vs <95%). SCF PTV coverage was also better with VMAT vs WT (99.5% vs 97.1%). For right-sided treatment, mean heart dose (MHD) was significantly higher with VMAT vs WT both in vDIBH (2.3 Gy vs 0.8 Gy, respectively (resp.), p<0.0001) and in FB (2.8 Gy vs 1.1 Gy, resp., p<0.0001). There was no difference in right MHD with vDIBH using VMAT (p=0.07), but vDIBH significantly reduces right MHD compared to FB when treating with WT (0.8 Gy vs 1.1 Gy, resp, p=0.004). For left-sided treatment, there was no difference in MHD with VMAT vs WT in vDIBH (p>1), but heart V17 Gy was significantly lower with VMAT (0.6 Gy vs 5.0 Gy, resp., p=0.0008). Ipsilateral lung constraints were consistently lower with VMAT, apart from the V5 Gy<50%. For right- sided RT, the contralateral (C/L) lung mean dose was higher with VMAT vs WT, regardless of whether breath hold was used (3.2 Gy vs 0.4 Gy, resp, p<0.0001) or not (3.0 Gy vs 0.4 Gy, resp., p<0.0001). For left-sided RT in vDIBH, the C/L lung mean dose was higher with VMAT vs WT (3.4 Gy vs 0.4 Gy, resp., p<0.0001). The C/L breast maximum dose was significantly lower with VMAT in vDIBH vs WT in vDIBH on the right (50.6% vs 99.8%, resp., p=0.0002) and left (49.4% vs 96%, resp., p=0.0001), as well as right VMAT in FB vs WT in FB (41.2% vs 102.3%, resp., p=0.0006). The C/L mean breast dose was consistently significantly higher in VMAT than WT, but similar in right-sided VMAT in FB vs VMAT in vDIBH (4.4 Gy vs 4.4 Gy, resp., p=0.49). Conclusion There is a dosimetric advantage to using vDIBH for right- sided RT that includes the IMC in terms of PTV coverage and reduction of MHD, particularly if using WT. VMAT allows for reduced lung doses for both left- and right-sided RT. The significance of contralateral mean breast dose needs to be studied further in terms of late effects risk. PO-0931 Lymphatic function and morphology in the arms of breast cancer treated women A. Johannessen 1 , B. Offersen 2 , M. Alstrup 3 , S. Mohanakumar 3 , V. Hjortdal 4 1 Department of Clinical Medicine, Department of Experimental Clinical Oncology- Aarhus University Hospital, Aarhus, Denmark ; 2 Department of Clinical Medicine, Department of Experimental Clinical Oncology and Department of Oncology- Aarhus University Hospital, Aarhus, Denmark ; 3 Department of Clinical Medicine, Research Department of Cardiothoracic and Vascular Surgery- Aarhus University Hospital, Aarhus, Denmark ; 4 Department of Clinical Medicine, Research Department of Cardiothoracic and Vascular Surgery- Rigshospitalet and Aarhus University Hospital, Aarhus, Denmark Purpose or Objective Adjuvant radiation therapy (RT) significantly improves survival in high-risk breast cancer (BC) treated with loco- regional RT, however, it also increases risk of lymphedema in particular in patients operated with axillary lymph node

dissection (ALND). ALND and nodal RT may partially obstruct lymph outflow from the ipsilateral arm, chronically raising the afterload of the lymphatic vasculature, which the lymphatic smooth muscle must overcome in order to secure sufficient drainage. Studies have shown a change in contractile function of the lymphatic vessels and demonstrated distinct lymphatic patterns in women diagnosed with breast cancer related lymphedema (BCRL), but no studies have investigated whether these changes occur before clinical edema is detectable, which is the focus of this study. Material and Methods The morphological and functional state of the lymphatic vessels is described using Near-Infrared Fluorescence (NIRF) imaging and plethysmography. The endpoints consist of contraction frequency, velocity, pumping pressure and capillary filtration rate (CFR). The study population is 35 high-risk BC patients included in the DBCG RT Skagen trial 1 and treated with loco-regional RT (50 Gy/25 fr or 40 Gy/15 fr). Patients are invited to participate in the study with an initial examination a few weeks after ended RT and a second examination 6-12 months later, which adds blood sampling for endothelial growth factor and cytokine analysis and a hyperthermia-protocol serving as a stress-test of the lymphatic vasculature to investigate the pumping capacity. Both arms will be examined enabling the patients to serve as their own controls. Results The preliminary results consist of 14 patients. Two patients so far presented with lymphatic abnormalities. A 22% higher pumping pressure was observed in the ipsilateral arm compared to the contralateral when patients with lymphatic abnormalities were excluded (p=0.0105). Patients with lymphatic abnormalities tend to perform a reduced maximal pumping pressure in the ipsilateral arm compared to the contralateral. Currently, no significant difference between the arms was present concerning frequency and CRF. All 35 patients will be accrued and have baseline examination during 2019, and most patients will have their second examination in the early spring of 2020. Conclusion The preliminary results indicate that the lymphatic vessels in the breast cancer related arm are compensating, for the damage inflected by the cancer treatment, by raising the ability to generate pressure. However, at some point the lymphatic vessels begin to develop lymphatic abnormalities and the ability to generate pressure weakens. These lymphatic abnormalities and reduced contractile function could be the initial phase leading to developing BCRL. By using NIRF and plethysmography this study investigates if these changes including biochemical markers can be used to evaluate early BCRL and guide early treatment, which at this point in time has proven to be much more beneficial. PO-0932 Preoperative radiotherapy for early breast cancer: quality assessment of the ROCK trial - NCT03520894 G. Francolini 1 , V. Di Cataldo 2 , S. Cipressi 2 , E. Scoccimarro 1 , V. Maragna 1 , L. Masi 3 , R. Doro 3 , G. Simontacchi 1 , I. Desideri 1 , I. Meattini 4 , L. Livi 4 1 Azienda Ospedaliera Universitaria Careggi, Radiation Oncology Unit, Florence, Italy ; 2 University of Florence - Istituto Fiorentino di Cura ed Assistenza, Radiation Oncology Unit- CyberKnife Center, Florence, Italy ; 3 IFCA, Department of Medical Physics and Radiation Oncology, Florence, Italy ; 4 University of Florence, Department of Biomedical- Experimental- and Clinical Sciences “Mario Serio”, Florence, Italy