ESTRO 36 Abstract Book

S20 ESTRO 36 2017 _______________________________________________________________________________________________

We enrolled 8 consecutive patients who were referred to the Radiological Department of our hospital for ECG-gated intravenous contrast enhanced CT. All scans were performed with the same multislice spiral CT (LIGHTSPEED, General Electric). Patients were asked to hold their breath after a mild hyperventilation. Reconstructions were performed in 10% steps over the entire R-R cycle with a dedicated retrospective ECG-gated algorithm. For all patients, 10 data sets were created and the following structures were delineated in the reconstructed sets: Left main trunk (LMT), left anterior descending (LAD), left circumflex artery (CX) and right coronary artery (RC). CA were contoured with inputs from an experienced radiologist. CA displacements across different phases of the heart cycle were evaluated in left– right (X), cranio-caudal (Y) and antero-posterior (Z) directions with the Van Herk formula (1.3 * Σ + 0.5 * σ). Results The following coronary displacements were found in X, Y and Z co-ordinates, repectively: 3.6, 2.7 and 2.7 mm for LMT; 2.6, 5.0 and 6.8 mm for LAD; 3.5, 4.5 and 3.7 mm for CX; 3.6, 4.6 and 6.9 mm for RC. Figure 1 shows the axial, coronal and sagittal contours of a right coronary artery, all retrieved on one of the ten sets created for each patient.

abdominal or thoracic free-breathing CBCTs, totaling 359 paediatric CBCTs and 374 CBCTs from adults (mean 12; range 2-33). To measure respiratory-induced diaphragmatic motion, a two-dimensional Amsterdam Shroud image was created for each CBCT, allowing for selection of the cranio-craudal position of the end-exhale (EE) and end-inhale (EI) positions of the top of the right diaphragm. Pixel coordinates were corrected for the scanner geometry and translated into millimetres relative to the patients’ isocentre. The amplitude was defined as the displacement between EE and EI diaphragm positions. The cycle time described the time between two consecutive EI peaks. We analysed the variability of the intrafractional and interfractinoal respiratory motion. Differences between children and adults were tested with the Mann-Whitney-U-test, considering p<0.05 significant. Results The differences in respiratory-induced diaphragmatic motion between children and adults are summarized in Figure 1. Although the mean amplitude was somewhat smaller in children than in adults (10.6 mm vs. 11.6 mm), the difference was small and insignificant. Interfractional variability in amplitude was significantly smaller in children compared to adults ( p=0.004 ). Since children breath faster than adults, the cycle time was significantly briefer ( p=0.000 ). Additionally, intrafractional variability in cycle time was also significantly smaller in children (p=0.002) .

Conclusion Our study shows that the CA displacement over the heart cycle ranges from 2.6 to 6.9 mm, suggesting the need for an IRV margin to accurately estimate the dose received by these structures during the planning of a thoracic irradiation. Based on these findings, we suggest to apply an isotropic margin of 3-4 mm for LMT and CX and an isotropic margin of 5-7 mm for LAD and RC. PV-0046 Comparison of respiratory-induced diaphragm motion during radiotherapy between children and adults S. Huijskens 1 , I. Van Dijk 1 , J. Visser 1 , C. Rasch 1 , T. Alderliesten 1 , A. Bel 1 1 Academic Medical Center, Radiation Oncolo gy, Amsterdam, The Netherlands Purpose or Objective Respiratory motion during radiotherapy has been extensively studied in adults and often 4-dimensional computed tomography (4DCT) is used to quantify the respiratory motion prior to treatment in order t o optimize safety margins. Similar data are not known for paediatric radiotherapy, and margins are therefore commonly based on adults data. The purpose of this study is to quantify and compare respiratory motion in children and adults. Material and Methods Respiratory-induced diaphragmatic motion was retrospectively analysed on repeated Cone Beam CTs (CBCTs) acquired during the radiotherapy treatment course of 35 children (mean age 10.7; range 2.2-17.8) and 35 adults (mean age 59.6; range 34.0-93.0). Patients were included when the diaphragm was visible on upper

Conclusion We found significant, but small, differences in respiratory- induced diaphragmatic motion between children and adults. Large ranges of amplitude and cycle time in both children and adults confirm that respiratory motion is patient-specific and requires an individualised approach to account for. Unexpectedly, overall variability is smaller in children than in adults, suggesting that a pre-treatment 4DCT for planning purposes will be at least equally beneficial in children as it is in adults. PV-0047 Whole lung irradiation in patients with osteosarcoma and Ewing sarcoma: a systematic review L. Ronchi 1 , E. Farina 1 , A. Zamagni 1 , V. Panni 1 , A. Arcelli 1,2 , A. Farioli 3 , A. Paioli 4 , S. Ferrari 4 , G.P. Frezza 2 , G. Macchia 5 , F. Deodato 5 , M. Ferro 5 , G. Torre 5 , S. Cilla 6 , A. Ianiro 6 , S. Cammelli 1 , A.G. Morganti 1 1 University of Bologna, Radiation Oncology Center- Department of Experimental- Diagnostic and Specialty Medicine - DIMES, Bologna, Italy 2 Ospedale Bellaria, Radiotherapy Department, Bologna, Italy