ESTRO 2021 Abstract Book

S1456

ESTRO 2021

document will harmonise how this technology is introduced internationally. [1] - Speight et al. (2019) https://doi.org/10.1088/1361-6560/ab2c7c [2] - Speight et al. (2021) https://doi.org/10.1088/1361-6560/abe9f7 [3] - Speight et al. (2021) https://doi.org/10.1088/1361-6560/abdc30

PO-1733 Python application to convert six shifts from image CBCT guidance into a singular correction T. Valdivielso Lopez 1 , D. Navarro 1 , E. Ambroa 1 , A. Infestas 2 , M. Lizondo 1 , A. Ramirez 1 , J. García-Miguel 1 , M. Colomer 1 1 Hospital de Terrassa, Radiotherapy, Barcelona, Spain; 2 Hospital de Terrassa, Radotherapy, Barcelona, Spain Purpose or Objective Image guided radiotherapy (IGRT) based on cone-beam CT (CBCT) provides accurate tumor localization when deriving setup corrections. The purpose of this work is to develop an in-house software that allows estimating the magnitude of the planning target volume (PTV) shift resulting from image registration setup errors. This application is used for stereotactic body radiotherapy (SBRT) treatments, where precise patient positioning is critical. Materials and Methods The HexaPOD Elekta couch correlated with CBCT enables sub-millimeter patient positioning accuracy in six degrees of freedom (6-DoF). Figure 1 shows the translational (x, y, z) and rotational (R x , R y , R z ) errors provided by the system.

We have designed a graphical user interface (GUI) implemented in the Tkinter Python package to compute the PTV shift regarding these 6-DoF through an algorithm that place us in the worst case scenario in terms of corrections. The application uses a database which includes the dimensions of the PTV for each patient and selects the PTV’s characteristic length as the radius of the PTV’s volume approximated to a sphere. This should be a good approach for most SBRT treatments. Results Before this application was developed, our IGRT protocol for SBRT treatments consisted in performing daily CBCT and registering with the planning CT until residual translational errors were < 1.5 mm and residual rotational errors were < 1º. For instance, 1.4 mm absolute errors and 0.9º errors in every direction will result in 3.5 mm total shift for a 33 cm 3 PTV’s volume (figure 2).