ESTRO 2023 - Abstract Book

S1665

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ESTRO 2023

Table 1: Calculated systematic, Σ , and random, σ , error for each sub-CTV, measured from daily kVCT imaging.

Conclusion Surface Guided Helical Tomotherapy for Total Marrow Irradiation can potentially improve patient positioning such that margins can be reduced with decreased dose to OARs while maintaining target coverage.

PO-1915 Larynx treatment: dose reduction in the carotids and plan robustness

H. Vivancos 1 , N. Jornet 1 , J. Perez-Alija 1 , C. Anson 1 , P. Gallego 1 , M. Barcelo 1 , N. Tejedor 1 , A. Dominguez 1 , N. Garcia Apellaniz 1 , F. Leo 1 , A. Ruiz-Martinez 1 , P. Carrasco de Fez 1

1 Hospital de la Santa Creu i Sant Pau, Medical Physics, Barcelona, Spain

Purpose or Objective Modulated treatment techniques have shown a better carotid sparing for larynx EBRT treatments. The aim of this study was to evaluate plan robustness (CTV and PTV coverage and dose to carotids) to inter-fraction rigid and not rigid positioning differences for 7 different EBRT techniques using X-rays. Materials and Methods 10 patients were included in the study. Patients were immobilised using a thermoplastic mask. GTV, CTV, PTV (CTV+5mm) and carotids were delineated. The dose prescription was 2 Gy x 35 fractions. A NAL5 + weekly CBCT was used for most patients. No corrections were applied if the Δ <3mm. For each patient 7 different treatment plans were prepared: 3D and IMRT & VMAT with the following avoidance volumes: none, shoulders (*) and shoulders & chin (**). The plans were optimised in Eclipse TPS to fulfil PTV D98 > 95%. An uncertainty planning study for each of the plans was performed by simulating 5mm rigid movements in the three axes. Then, the dose distribution for each plan was recalculated in Eclipse using the weekly CBCTs. Finally, the results of an in vivo system, using 2D EPID transmission dose and logfile based dose recalculation on the CBCT were compared for the real patient treatment (7 3DCRT; 1 IMRT**; 2VMAT**).