ESTRO 37 Abstract book

S1110

ESTRO 37

5 Istituto Europeo di Oncologia and University of Milan, Division of Radiation Oncology and Department of Oncology and Hemato-oncology, Milano, Italy 6 Istituto Europeo di Oncologia, Unit of Medical Physics- European Institute, Milano, Italy 7 University of Milan and Istituto Europeo di Oncologia, Department of Oncology and Hemato-oncology and Department of Medical Imaging and Radiation Sciences, Milano, Italy 8 Politecnico di Milano and Centro Nazionale di Adroterapia Oncologica, Dipartimento di Elettronica Informazione e Bioingegneria and Bioengineering unit, Milano and Pavia, Italy Purpose or Objective Lung Optimized Treatment (LOT) is an innovative CyberKnife procedure that provides three fiducial-less motion management approaches. In 2-view (2V) the tumor is visible in both orthogonal X-ray images and full motion tracking is performed. In 1-view (1V) the tumor is visible in a single X-ray image, therefore motion tracking is combined with an internal target volume (ITV)-based margin expansion. In 0-view (0V) the lesion is not visible, consequently the treatment relies entirely on an ITV- based approach. The aim of the study is the evaluation of target coverage in the above-mentioned modalities. Material and Methods We analyzed data of 30 patients treated with LOT from November 2014 to February 2017 at Radiotherapy Division of European Institute of Oncology (Milan, Italy). Only 2V patients were selected since they provide comprehensive information on the three-dimensional tumor motion in correspondence to each X-ray image. Treatments in 1V and 0V modalities were simulated from these data by processing log files and planning volumes. In our Institution, planning target volume (PTV) margins are defined according to the tracking modality: end- exhale clinical target volume (CTV) +3mm in 2V and ITV + 5mm in 0V. In the 1V scenario, the ITV encompasses only tumor motion along the non-visible direction. Then, non- uniform ITV to PTV margins are applied: 3 mm and 5 mm in the visible and non-visible direction, respectively. CTV and PTV positions were derived from treatment log files according to the specific tracking modality. Then, a coverage measure was calculated as the intersection between CTV and PTV volumes in correspondence to each image acquired during irradiation. Similarly to dose- volume histogram, CTV coverage-volume histograms are derived for each patient and treatment modality. Results In Fig.1, the coverage-volume histogram curves report the Y% of the CTV that is within the PTV in at least X% of control images acquired during treatment. The coverage of the 95% of the CTV is defined as C95%. The median values of C95% among the patient population are comparable for the three tracking modalities and larger than 98.1%.

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 PTV margins are adequate to compensate tracking errors and tumor motion in all LOT treatment modalities. Since stereotactic body radiotherapy ensures high dose