ESTRO 38 Abstract book

S1077 ESTRO 38

simulation in both free breathing (FB) and mDIBH setup. The Elekta ABC spirometer was used for respiratory control and breath-hold period of 20–30 s. A simultaneously integrated boost (SIB) plan was created for both simulation CTs (FB and mDIBH) consisting of a prescription dose of 50 Gy to the whole breast and 60 Gy to tumor bed in 25 fractions. The heart and the left ventricle were contoured according to the Feng et al. heart atlas. Dose volume histograms were analyzed to assess the heart mean dose (MHD) and the volume of left ventricle receiving 5Gy (V5), since these dosimetric metrics have been demonstrated to be the best predictors of acute cardiac events. Data were analyzed using a Wilcoxon signed-rank test with a level of significance set at p< 0.05. Results The use of ABC mDIBH resulted in similar target coverage with no significant statistical differences. For PTV1 median D95% and V95% were 58.5 Gy (range: 57.3-59.5 Gy) and 98.6% (range: 96.0-100.0%) in FB, and 58.5 Gy (range: 57.0-60.1 Gy) and 98.7% (range: 95.0-99.9%) in mDIBH. For PTV2 D95% and V95% were 48.8 Gy (range: 43.4-50.5 Gy) and 97.0% (range: 91.4-99.4%) in FB and 49.3 Gy and 98.0% (range: 92.3-99.8%) in mDIBH. Median MHD was 3.7 Gy (range:2.8-6.2 Gy) in FB and 2.5 Gy (range:1.6-4.1 Gy) in mDIBH (p<0.05), resulting in absolute and relative reduction of 1.3 Gy (range: 0.2-2.5 Gy) and 35.0% (range: 4.7-53.6%), respectively. Median LV-V5 was 27.4% (range:1.8-44.0%) in FB and 8.2% (range:0.0-25.9%) in mDIBH (p<0.05). The use of ABC mDIBH reduced MHD by 20% or greater and LV-V5 by 35% or greater in 90% of patients. Conclusion The use of the ABC spirometer for mDIBH resulted in a significant reduction in cardiac dose for left sided breast radiotherapy. The significant cardiac dose sparing may translate in reduction of excess risk of acute cardiac events. EP-1974 Usage of computer generated 4D CTs for interplay effect studies in scanned proton therapy T. Pfeiler 1,2,3 , C. Bäumer 1,2,4 , E. Engwall 5 , D. Geismar 1,2,4,6 , U. Mäder 7 , B. Spaan 3 , B. Timmermann 1,2,4,6 , J. Wulff 1,2,7 1 University Hospital Essen, West German Proton Therapy Centre Essen WPE, Essen, Germany ; 2 University Hospital Essen, West German Cancer Centre WTZ, Essen, Germany ; 3 TU Dortmund University, Experimental Physics 5, Dortmund, Germany ; 4 German Cancer Consortium DKTK, Radiation Oncology and Imaging, Heidelberg, Germany ; 5 RaySearch Laboratories AB, Development, Stockholm, Sweden ; 6 University Hospital Essen, Department of Particle Therapy, Essen, Germany ; 7 TH Mittelhessen, Radiation Protection Institute, Gießen, Germany Purpose or Objective There is a need for realistic 4D data-sets in radiation therapy, especially in scanned proton therapy to systematically investigate interplay effects for moving targets. The production of physical phantoms representing the entire spectrum of patients is generally not feasible and the availability of suitable, clinical 4D CTs is limited. Recently, the 4D XCAT phantom, a whole-body computer model of human anatomy and physiology, became available and allows generation of virtual 4D CTs (v4D CTs). Their application was tested in a proof-of-concept study investigating the magnitude of interplay effects as a function of the target size for one patient with different CTVs. Material and Methods A 4D XCAT chest CT was imported to RayStation 7. In addition to a set with typical clinical CT-numbers for treatment planning, a copy with image-values representing organ IDs was imported. The segmentation tools thereby allowed to perfectly map organs in all 4D CT

Conclusion A simple, robust and reliable approach (TGRT) has been validated to correct patient positioning shifts. TGRT may add intra-fraction monitoring capabilities to conventional IGRT by providing real-time convergent corrections after every beam irradiation. Initial testing in patients and model extrapolation to VMAT techniques are work in progress. This work was partially financed by FIS PI15/00788. EP-1973 Cardiac dose sparing with active breath coordinator in breast radiotherapy: a dosimetric analysis A. Ianiro 1 , M. Boccardi 2 , G. Macchia 2 , F. Deodato 2 , P. Viola 1 , M. Craus 1 , V. Picardi 2 , M. Ferro 2 , M. Ferro 2 , E. Arena 2 , A. Pierro 3 , M. Buwenge 4 , F. Romani 5 , A.L. Angelini 5 , V. Valentini 6 , A.G. Morganti 4 , S. Cilla 1 1 Fondazione di Ricerca e Cura "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, Medical Physics Unit, Campobasso, Italy ; 2 Fondazione di Ricerca e Cura "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, Radiation Oncology Unit, Campobasso, Italy ; 3 Fondazione di Ricerca e Cura "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, Radiology Department, Campobasso, Italy ; 4 Department of Experimental Diagnostic and Specialty Medicine - DIMES - University of Bologna, Radiation Oncology Department, Bologna, Italy ; 5 Department of Experimental Diagnostic and Specialty Medicine - DIMES - University of Bologna, Medical Physics Unit, Bologna, Italy ; 6 Fondazione Policlinico "A. Gemelli"- Università Cattolica del Sacro Cuore, Radiation Oncology Department, Roma, Italy Purpose or Objective Cardiac toxicity is a major concern for left breast tangential field irradiation. Moderate deep inspiration breath hold (mDIBH) during radiation treatment delivery helps in reducing the cardiac dose. In this dosimetric study, the doses to heart were compared between free- breathing (FB) and mDIBH during tangential IMRT breast irradiation. Material and Methods Twenty consecutive patients with left-sided breast cancer who underwent adjuvant tangential IMRT with ABC mDIBH were analyzed in this study. All patients underwent CT