Abstract Book

S1110

ESTRO 37

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) 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 between the gating and the delivery system) were performed. right - / left + anterior - / posterior + inferior -

The lesion selected was a thymoma: Patient1 treated with 66 GyRBE, Patient2 with 54 GyRBE. An amplitude based reconstructed 4DCT (10 phases) and a free-breathing CT (FBCT) were acquired and used for the planning. The physician copied the CTV from each phase of the 4DCT to the FBCT to create the ITV. By using the deformable registration, each OAR was mapped and verified from the FBCT to each phase of the 4DCT. The planning was performed on the FBCT. The approved plan was evaluated in two ways: - It was recalculated on each phase to find the worst case scenario in terms of OAR overdosage - Interplay effect: every spot was assigned to a phase accordingly to the beam delivery and the breathing curve of the patient. The 10 doses were then deformed on the FBCT and summed to evaluate if the dose homogeneity to the target and the constraints to the OAR were deteriorated and violated. During treatment delivery accurate gating was ensured allowing automatic beam hold when the breathing amplitude was higher than the one measured during 4DCT scan. Results The validation of the gating technique ensured a good quality of the beam delivery with out-of-threshold interruptions. The timing between the gating off signal and the interruption of the beam was always below 90ms (maximum allowed was 100ms). The evaluation of dose on each phase and of the interplay effect gave the results shown in table for both patients. The coverage of the ITV was always ensured and the OARs were always within the constraints: no interplay effect was highlighted. The second patient showed an overdosage to the coronary and Left Anterior Descending area respect to the nominal plan but it was always below the constraints. The table shows the average and the worst Duty Cycle (DC) per fraction during the entire treatment. Two examples of breathing curves are provided in figure. The breathing of the first patient is stable and always within the gating thresholds, whilst for the second patient more amplitude and phase variations are present, with multiple beam interruptions due to the out-of- threshold amplitude signal.

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