ESTRO 2023 - Abstract Book

S2054

Digital Posters

ESTRO 2023

Purpose or Objective Current guidelines recommend Pulmonary Veins (PVs) isolation with catheter ablation (CA) in patients affected by atrial fibrillation, refractory to antiarrhythmic therapy. A non-invasive Linac-based approach was studied in the phase II trial on STereotactic Arrhythmia Radioablation for atrial fibrillation. The present analysis aims to evaluate the displacements of targets motion during respiratory phases. Materials and Methods A vac-lock bag was used for patients’ immobilization in the supine position. Three Computed Tomography (CT, 1mm slice- thickness) were performed: 1) free-breathing CT for dose calculation; 2) 4-Dimension CT (4D-CT) for moving evaluation; 3) CT with contrast for anatomical accuracy. The clinical target volume (CTV) was identified by radiation oncologist and cardiologist and was defined as the area around PVs, generating 2 separate target volumes, one around the left PVs and the other one on the right PVs. All CTVs were propagated to all respiratory phases scans. Based on 4D-CT, the internal target volume (ITV) was generated from CTVs to encompass heart and respiratory movements. Medial-lateral (M-L), anteriors-posterior (A-P) and superior-inferior (S-I) displacements for center of mass of CTVright and CTVleft were evaluated during all respiratory phases on 4D-CT. Results From May 2021 to July 2022, 18 elderly patients were treated: median age was 77,6 years old (range 71-90). In terms of 4D-CT data, a total of 288 CTVs were analyzed (144 CTVS right and 144 CTVs left). the average M-L, A-P and superior- inferior S-I displacements for CTVright and CTVleft were -0.008; 0.001; 0.05; 0.004; -0.04; 0.03 cm, respectively, However, only S-I movements reported a maximum amplitude of 0.6 cm, while for M-L and A-P an amplitude of 0.1 cm was documented. Conclusion CTVleft and CTVright displace laterally, A-P and S-I on average of few millimeters (max amplitude 0-0.6 cm). The displacements of CTVLeft and CTVRight were similar during respiratory phases, even if it seems than CTVright was more mobile respect to left for M-L and A-P displacements. In the present cohort of patients treated with STereotactic Arrhythmia Radioablation for atrial fibrillation, 4D-CT emerged as an effective and sufficient tool to valuate target displacement due to internal motion. Consequently, Deep Inspiration Breath Hold or Respiratory gated radiotherapy may be unnecessary. D. Hernandez 1 , P. Castro 1 , M. Roch 1 , P. Chamorro 1 , S. Honorato 2 , M.S. Talaya 3 , R. Rubiato 3 , A. Valiente 3 , S. Carroceda 3 , M. Escobar 3 1 H.U. La Princesa, Medical Physics, Madrid, Spain; 2 H.U. La Princesa, Medical Physics, madrid, Spain; 3 H.U. La Princesa, Radiation Oncology, madrid, Spain Purpose or Objective A good immobilization in radiotherapy treatments allows delivering the dose as accurately as posible each day of treatment. Currently, there are many comercial solutions for cranial immobilization. This study aims to analyze the reproducibility of the treatments achieved with two different head and neck immobilization devices. Materials and Methods Forty patients have been analyzed, 30 of them have been treated with shoulder thermoplastic devices manufactured by A (MA) and 10 patients have been treated with head and neck immobilization manufactured by B (MB). Eighteen patients have been treated in a TrueBeam, with the Varian Perfect Pitch 6 degrees of freedom (6DoF) and 26 patients have received their treatment in a Clinac 2300-iX, with the VARIAN Exact IGRT couch 4 degrees of freedom (4DoF). All of them have been immobilized with shoulder thermoplastic mask. The offset applied in the longitudinal, lateral, vertical and rotation have been analyzed. Patients treated in the TrueBeam, have also been studied the pitch and roll displacements. All images have been examined in the Eclipse offline review. Results Patients treated with the thermoplastic mask MA presented offsets in the vertical, longitudinal and lateral axis very similar to the patients treated with MB device. Theses offsets are less than 0.1 cm. Analysing devices by machines, in the Clinac 2300-iX it can be seen how rotational displacements are much higher with the MA device than MB immobilizer (image1) In the TrueBeam it is observed that the offsets in pitch and rotation axes are also more than doubled with MA immobilizer than MB thermoplastic mask. The analysis of all patients, independent of the machine, is shown in image2. It is observed that the displacements in all axes are higher in MA than MB, except in the roll axis. The registration of the images has also been analysed visually. It has been found that the position of the shoulders is much more reproducible with the MB masks. PO-2284 Head and neck immobilization masks: comparative between two different manufacturers