ESTRO 2023 - Abstract Book

S1775

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ESTRO 2023

fraction was 9.3 minutes (IQ range: 8.6-10.5). The lesion’s maximum transverse diameter of the lesion was 5 cm. Compared with LINAC based plans, a median GTV/PTV ratio reduction of 20.8% was calculated. With a median follow up of 15 months, approximately 67% of patients developed radiological toxicity, mostly asymptomatic or with mild symptoms. Only 3 patients displayed acute G2 toxicity: asthenia, cough, and dyspnoea. No severe pneumonitis of grade 3 or higher was detected. Conclusion Our preliminary analysis show the safety and feasibility of Synchrony® tumor-tracking system on a heterogeneous cohort of selected patients with lung lesions. This advanced technical solution allows a reduction of the PTV volume compared to a LINAC based technique without tumor tracking, with an overall treatment time limited to less than 10 minutes and no increased toxicity or discomfort even in more fragile patients. D. Finocchiaro 1 , M. Orlandi 2 , D. Lambertini 2 , G. Sceni 2 , A. Barani 2 , V. Bertolini 2 , V. Trojani 2 , R. Sghedoni 2 , M. Iori 2 , C. Iotti 3 , F. Iori 3 , L. Cozzi 3 , A. Botti 2 1 AOU Modena, Medical Physics Unit, Modena, Italy; 2 Azienda USL di Reggio Emilia, Medical Physics Unit, Reggio Emilia, Italy; 3 Azienda USL di Reggio Emilia, Radiotherapy Unit, Reggio Emilia, Italy Purpose or Objective Lattice radiotherapy (LRT) is a 3D implementation of Spatially Fractionated Radiation Therapy and is based on the creation of a lattice-like dose distribution with spherical areas of high-dose (vertices) interspaced within a background of low-dose (valley). Due to the vast heterogeneity of tumour shapes, the problem of finding the best lattice arrangement is not trivial. Manual arrangement can involve sub-optimal solutions and is time-consuming. The aim of this study was to develop a home-made tool (LRT Optimizer) that automatically generate the optimal lattice structure. Performances of this tool were validated on clinical cases. It uses as input parameters CT image, GTV structure and sphere diameters (user editable) and generates the optimal Lattice structure as a DICOM-RT. The automatic tool finds the 3D-spatial configuration that maximize the number of vertices within the GTV and minimize the OVH (overlapping volume histogram) with the OARs (user-selected with a GUI). In this study, LRT Optimizer was validated on a cohort of seven patients. For each patient, a lattice structure with sphere of 1.5cm diameter and 6cm spaced was generated. As an example, the lattice structure and the GTV are plotted in Figure 1. LRT Optimizer was validated in terms of number of vertices and OAR dose sparing. For each patient, two OARs were selected. The number of vertices were verified with visual inspection. To validate the OVH optimization, for each patient two different treatment plans were performed: the one based on the lattice structure that minimize the OVH (Plan optimized) and the one that maximize the OVH (Plan unoptimized). These two plans were generated using the same optimization function template in Eclipse version 13.7, hence the different result is only attributable to the different lattice configuration. Materials and Methods The LRT optimizer has been developed in MATLAB 2022a. PO-2002 development of an automatic tool for lattice radiotherapy treatment optimization

Results For each patient, it was verified by manual inspection that the lattice structures had the maximal possible number of vertices within the GTV. Comparison between Plan optimized and Plan unoptimized (Table 1) showed that OAR dose sparing was achieved for each clinical case and average 6% dose sparing was obtained. Table 1: Absorbed dose percentage difference between ‘Plan optimized’ and ‘Plan unoptimized’ for vertices and OARs for each patient.

Patient number Dose difference(%) in Vertices Dose difference(%) in OAR1 Dose difference(%) in OAR2 1 0.08 -0.73 -1.17