ESTRO 37 Abstract book

S1112

ESTRO 37

lower, with respect to the renal hilum Figure 1 . Deformable-registration was performed in RayStation TM (RaySearch Laboratories AB, Stockholm) using phase 0% as the reference image. Deformation vector field (DVF) displacement of voxels within these structures was used to estimate motion for the upper, middle and inferior portions of right and left kidneys. Results Mean (SD) DVF displacements of segmented right and left kidneys are illustrated in Table 1. The published finding that intrafraction motion of the kidney, as described using COM, is smaller in magnitude compared to adults and is greatest in the superior/ inferior (S/I) direction is supported by our data (Uh 2017, Kannan 2016, Panandiker 2012). In addition, our results also suggest variable motion between right and left kidneys; differential motion was seen between upper and lower segments of the left kidney; 1.2 (1.5) and 0.7 (0.6) respectively. The same segments of the right kidney moved relatively rigidly as shown by more consistent mean and SD DVF displacements; 0.8 (1.4) and 0.8 (1.2). Table 1. Kidney motion according to DVF displacement Grand mean (1SD) mm superior + Right upper kidney -0. 1 (0.2) 0.2 (0.4) 0.8 (1.4) Right middle kidney 0.0 (0.2) 0.3 (0.4) 0.8 (1.2) Right lower kidney 0.1 (0.2) 0.3 (0.6) 0.8 (1.2) right - / left + anterior - / posterior + inferior - / Left upper kidney -0.1 (0.2) 0.3 (0.9) 1.2 (1.5) Left middle kidney -0.2 (0.2) 0.2 (0.4) 0.8 (0.9) Left lower kidney -0.2 (0.2) 0.2 (0.4) 0.7 (0.6) Conclusion For children and young people kidney motion is greatest in the S/I direction. The right kidney displays rigid motion and the left upper kidney displays greater excursion S/I than the lower segment. Right/ left motion in children and young people is negligible but more variation is evident in the anterior/ posterior direction which could have implications for intensity modulated proton beam planning as such motion could affect the radiological depth of the target. EP-2032 Implementation of 4D proton therapy treatments with pencil beam scanning (PBS) F. Fracchiolla 1 , F. Dionisi 1 , S. Hild 2 , I. Giacomelli 1 , S. Lorentini 1 , E. Engwall 3 , P.G. Esposito 4 , M. Amichetti 1 , M. Schwarz 1 1 Ospedale Santa Chiara di Trento, Centro di Protonterapia, Trento, Italy 2 TIFPA, Trento Institute for Fundamentals Physics Applications, Trento, Italy 3 RaySearch Laboratories, Stockholm, Sweden 4 Università degli Studi di Trento, Fisica, Trento, Italy Purpose or Objective To report on the implementation, validation and results of the first 2 proton therapy (PT) PBS treatments of small amplitudes moving targets performed at our PT center. Material and Methods A real time optical tracking of respiratory motion (Vision RT®) was used to monitor the patient during the CT scan and treatment. We interfaced it with the delivery system to trigger the beam every time the amplitude of the breathing was out-of-threshold. Validation measurements on the machine (i.e. verifying the communication time

cm radius was calculated (within the acquired images a high intensity corresponds to low tissue density), as well as the relative angle θ of the FM towards the imager. The resulting values were then evaluated regarding the success of the FM (2D-)detection of every imager individually as well as against the combined 3D- detection. Based on the obtained information, the density of the successful FM detection S(X) and of the failed detections F(X) depending X ∈ {I,θ} on were calculated. The ratio S(X)/F(X) was used to check for dependencies of the FM detection rate depending on either the surrounding intensity or the relative angle of the marker towards the imager. By performing this evaluation not only for the combined detection, but for every imager individually as well, a difference of the two imagers could be made visible. Results The ratio S(X)/F(X) shows, that the detection probability does not depend on the relative angle of the FM towards the imager. However an increase of this ratio for increasing intensities, and thus higher marker contrast, could be observed. This shows that a FM implantation in line of sight with tissues of low density can improve the FM detection. Additionally our results show that the detection is more reliable within images taken by imager 1. A following analysis with the TOR 18FG (Leeds Test Objects, Boroughbridge, United Kingdom) phantom revealed that during DTT the contrast of imager 2 is about 3 times lower compared to imager 1. This effect is not visible in kV images acquired without using DTT. Conclusion It could be shown that the FM detection of the Vero system is not dependent on the relative angle of the marker towards the imager, but shows a dependency on the intensity surrounding the FM within the acquired kV images. A higher FM detection rate within imager 1 leads to further examinations of the imaging process during DTT. EP-2031 Kidney motion in children and young people quantified using 4DCT deformable registration N. Lavan 1 , D. Mc Quaid 2 , G. Smyth 2 , S. Vaidya 3 , F. Saran 4 , U. Oelfke 5 , H. Mandeville 3 1 Institute of Cancer Research, Radiotherapy and imaging, London, United Kingdom 2 The Royal Marsden NHS Foundation Trust, Joint Department of Physics, London, United Kingdom 3 The Royal Marsden NHS Foundation Trust, Children's and Young Person's Unit, London, United Kingdom 4 The Royal Marsden NHS Foundation Trust, Department of Neuro-Oncology, London, United Kingdom 5 Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Joint Department of Physics, London, United Kingdom Purpose or Objective Kidneys are the principle dose-limiting organ for abdominal RT in children and young people. Centre of mass (COM) measurement is a frequently reported descriptor of respiratory-related organ motion but is insensitive to changes in organ shape. Deformable image registration of 4DCT is an alternative method of measuring intra-fraction changes in structure geometry reflecting both deformation and translation in x, y and z. This work is the first to apply this methodology to 4DCT in children and young people. Material and Methods 15 patients having upper abdominal RT and simulation 4DCT were analysed; median age 4 (range: 1 - 17 years). 13 right and 10 left kidneys in total were included. Following acquisition, 4DCTs were retrospectively sorted into 10 phase bins; 0 – 90%. Kidneys were contoured on all image sets by the same clinician to minimise intraobserver delineation variation. Kidney structures were divided into three segments; upper, middle and