ESTRO 2020 Abstract Book

S866 ESTRO 2020

rpm) were simulated using a programmable motion phantom (QUASAR Modus QA). The phantom with imaging inserts of density 1.41 gcm -3 , including 2 spheres S1 and S2 of 1 and 2 cm diameter, respectively, and a cube (D3) of edge 3 cm was scanned by 4D-CT (Philips big Bore) and 4D- CBCT (acquired with Elekta XVI) under the 16 breathing modes registered. The image datasets were transmitted to the MIM workstation, and the inserts were automatically contoured on each phase by HU thresholding, and then verified by the reference radiation oncologist. The volumes of each insert were recorded and the results obtained in the different phases for both modalities were analysed and compared with Friedman test, and p < 0.05 was considered statistically significant. Results The comparison between the volumes of the inserts and their corresponding 4D-CT and 4D-CBCT contoured volumes was performed when all the breathing patterns were considered. The results showed a mean percent increase in the volume of 60.9%±29%, 33.4%±16.1%, and 30.2%±14.1% for the 4D-CT, 56%±10.1%, 7.6%±6.6%, and 17.2%±6.5% for the 4D-CBCT and for the S1, S2, and C3 inserts, respectively. Figure 1 shows the volumes of the three contoured inserts under different imaging modalities and breathing patterns vs breathing phases. The results obtained for the 4D-CT S1, S2, C3 contoured volumes (Figure 1a, b, c, respectively) show a plateau for each breathing patterns between phases 40 to 70%. In this range of phases, the mean percent increase of the volume, was reduced to 35.6%±8.4%, 16.2%±4.9%, and 23.2%±4% for S1, S2, C3, respectively. The graphs in Figure 1d, e, f, representing the 4D-CBCT S1, S2, C3 volumes, respectively, show a lower increase of the contoured volumes, and a lower volume variability along the whole interval of phases. Moreover, the mean percent increase in the S1, S2, C3 volumes calculated in the phase interval 40-70% is 50.0%±12.0%, 8.3%±6.9%, and 16.6%±5.2%, respectively, and remain close to the values obtained using the whole interval of phases.

are shown in Table 1; they presented no significant difference (p <0.05), leading to a mean increase in the volume of the insert that remain constant along this range of phases.

Conclusion A phased 4D-CT dataset selected as reference CT images on the basis of constant volume could be used as reference for the target delineation and for registration with 4D- CBCT imaging in order to improve the treatment accuracy. PO-1593 Impact of left ventricular V5 on acute coronary event cumulative risk in breath-hold breast IMRT C. Romano 1 , A. Ianiro 1 , F. Deodato 2 , G. Macchia 2 , M. Boccardi 2 , V. Picardi 2 , M. Ferro 2 , M. Ferro 2 , M. Craus 1 , A. Pierro 3 , E. Scirocco 4 , M. Buwenge 4 , S. Cammelli 4 , C. Sacra 5 , C.M. De Filippo 6 , V. Valentini 7 , A.G. Morganti 4 , S. Cilla 1 1 Fondazione di Ricerca e Cura Giovanni Paolo II, Medical Physics Unit, Campobasso, Italy ; 2 Fondazione di Ricerca e Cura Giovanni Paolo II, Radiation Oncology Unit, Campobasso, Italy ; 3 Fondazione di Ricerca e Cura Giovanni Paolo II, Radiology Department, Campobasso, Italy ; 4 DIMES Università di Bologna, Radiation Oncology Department, Bologna, Italy ; 5 Fondazione di Ricerca e Cura Giovanni Paolo II, Cardiology and Hemodynamics Unit, Campobasso, Italy ; 6 Fondazione di Ricerca e Cura Giovanni Paolo II, Cardiovascular Surgery Department, Campobasso, Italy ; 7 Fondazione Policlinico Universitario “A. Gemelli, Radiation Oncology Department, Roma, Italy Purpose or Objective Cardiac toxicity is a major concern for left breast tangential field irradiation. Recent analyses reported a strong relationship between volume of the left ventricle receiving 5 Gy (LV-V5) and acute coronary event (ACE). Moderate deep inspiration breath hold (mDIBH) during radiation treatment delivery helps in reducing the cardiac dose. The aim of this study was to quantify how the use of active breath control (ABC) in mDIBH during tangential IMRT breast irradiation translated in a reduction of ACE Twenty consecutive patients with left-sided breast cancer who underwent adjuvant tangential IMRT with ABC mDIBH were analyzed in this study. All patients underwent simulation CT of both free breathing (FB) and mDIBH. The Elekta ABC spirometer was used for respiratory control and breath-hold length 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 whole breast and 60 Gy to tumor bed in 25 fractions and tangential IMRT technique. ACE cumulative risk was calculated using the prediction model developed by van den Bogaard et al., depending on LV-V5, patient age and pretreatment risk factors. A weighted ACE risk score was used for the patient cohort (0 for no risk, 0.8 for diabetes, 1.4 for hypertension and 1.8 for history of ischemic cardiac events). ACE cumulative risk was calculated four times for each patient (once for each pretreatment risk factor) simulating four cohorts grouped on the basis of the four risk factors. excess cumulative risk. Material and Methods

The mean absolute volumes of the 4D-CT and 4D-CBCT contoured volumes, for each phase between 40 and 70%