Abstract Book

S1108

ESTRO 37

Results A total of 128 cine-MR series originating from 11 patients were analyzed. The largest tumor motion was found in CC direction, with a mean peak-to-peak motion of 10.9 mm (standard deviation [SD] 4.9 mm), followed by AP with 3.5 mm (SD 1.9 mm) and LR with 2.6 mm (SD 1.4 mm). Large variations in intra-fraction motion were found within and between patients. The presence of a severe inhale was found in 5 of the 128 scans (4%). After exclusion of these scans mean peak-to-peak motion was 10.3 mm (SD 3.8 mm). Correction for drift showed a reduction in mean peak-to-peak motion to 9.5 mm (SD 3.3 mm). Reduction of the motion is visualized in Figure 2. Despite correction, large variations in tumor motion between measurement points within patients was observed.

conformity to target volume, the reported converge measures could be indicative of the dose distribution that would be obtained through the different treatment modalities. EP-2028 Quantifying intra-fraction motion in esophageal tumors throughout nCRT based on cine-MRI S.E. Heethuis 1 , A.S. Borggreve 1 , L. Goense 1 , P.S.N. Van Rossum 1 , S. Mook 1 , R. Van Hillegersberg 2 , J.P. Ruurda 2 , G.J. Meijer 1 , J.J.W. Lagendijk 1 , A.L.H.M.W. Van Lier 1 1 UMC Utrecht, Department of Radiotherapy, Utrecht, The Netherlands 2 UMC Utrecht, Department of Surgery, Utrecht, The Netherlands Purpose or Objective To noninvasively quantify intra-fraction motion of esophageal tumor throughout the course of neoadjuvant chemoradiotherapy (nCRT) using 2D cine-magnetic Patients treated with nCRT for esophageal cancer underwent six sequential MRI scans. Scans were acquired prior to the start of treatment, followed by five weekly MRI scans during neoadjuvant treatment. Cine-MR series were acquired in the coronal and sagittal plane (1.6/1.7 Hz, respectively) with a resolution of 2.01x2.01 mm during approximately 45 seconds. Two cine MR series were acquired separated by approximately 10 minutes. Tumor motion was assessed in cranio-caudal (CC), anterior-posterior (AP) and left-right (LR) direction (see Figure 1). CC-motion patterns were further analyzed for the presence of a tumor drift, quantified as the variations in mid-position between inhale and exhale peaks. Furthermore, large inhales were identified by detecting outliers in the comparison between 0th and 10th percentile (P0/P10) for each motion curve. resonance (MR) series. Material and Methods

Conclusion Intra-fraction motion was found to be highly variable between patients. Furthermore, motion within patients was found to be variable over the different measurement points. Correction for severe inhales and drift reduced motion amplitudes. This indicates that real-time tumor motion management during radiotherapy is desired to safely reduce margins. EP-2029 Intrafractional baseline drift in SBRT of liver tumors J. García Ruiz-Zorrilla 1 , M.A. De la Casa de Julián 1 , C. Rubio Rodriguez 2 , P. Fernández Letón 1 , J. Martí Asenjo 1 , D. Zucca Aparicio 1 , O. Hernando Requejo 2 , X. Chen Zhao 2 , B. Alvarez Rodríguez 2 , R. Ciérvide Jurio 2 , J. Valero Albarrán 2 1 Hospital Universitario HM Sanchinarro, Radiofísica, Madrid, Spain 2 Hospital Universitario HM Sanchinarro, Oncología Radioterápica, Madrid, Spain Purpose or Objective To investigate the frequency and amplitude of baseline or drift of liver tumors in stereotactic body radiation therapy (SBRT), using a gating respiratory system radiation therapy with intra-fractional IGRT. Material and Methods 55 fractions of 16 patients with liver tumors were treated with SBRT using ExacTrac Adaptive Gating® in a Novalis® linac. This system uses external markers to control the