ESTRO 2022 - Abstract Book

S1359

Abstract book

ESTRO 2022

treatment, and b) MC simulation of three 5x5 cm 2 fields lung treatment on the ICRP110 phantom. A graphical user interface (GUI) was created to calculate the PPD 3D distribution on any CT. Results Maximum differences between our PPD model prediction and the data from the MC lung plan and measured data from VMAT plan, were 29 and 9 and mGy/Gy, respectively. The PPD distribution on the abdomen (isodoses on a coronal plane) is depicted in figure 1. A screenshot of the GUI for the lung plan showing the PPD on a transversal view is shown in figure 2. The GUI allows for fast visualization of the 3D dose distribution in a loaded CT and the dosimetric information (DVH, maximum, minimum, and average organ dose) of outlined organs (in this example, heart)

Figure 1 Coronal view of PPD dose distribution on the ICRP110 of the eight-field abdomen plan. The central region is not shown as it belongs to the volume inside the 5% isodose, which is not considered by the model.

Figure 2 Upper left shows PPD at a transversal plane on the ICRP110 in a lung treatment (dose normalized to the slice). The upper right window shows the PPD on the organ (heart in this case). The cumulative DVH for the organ is depicted. Conclusion A relatively simple model (Periphocal 3D) was generated. It allows for a fast 3D calculation of PPD in isocentric treatments with coplanar beams. This information is essential for a more accurate estimation of secondary cancer risk at the organ. In addition to that, and as a first step to translating the research to the clinic, a GUI was created in MATLAB for 3D visualization of PPD calculated on any whole-body CT (see abstract E22-1144). The GUI allows visualization of PPD distributions, as well as the DVH of out-of-field organs.

Acknowledgments: Fondecyt N1181133

PO-1577 Effective measurement plane for VMAT QA in MatriXX Evolution and the new MatriXX Resolution

I. Petrov 1 , T. Lazhovski 1 , Y. Kirpichev 2 , D. Ganchev 1

1 Heart and Brain Center of Clinical Excellence, Medical Physics, Pleven, Bulgaria; 2 Medscan LLC, Medical Physics, Moscow, Russian Federation Purpose or Objective Pretreatment QA is especially important for state of the art techniques such as VMAT. Common method is to compare in specialized software dose planes measured with 2D detector arrays in phantom with corresponding planes from TPS dose distributions calculated in the phantom studyset. This work aims to evaluate for practical purposes the difference between the phantom/array setup plane and the effective plane of measurement, as well as the need to apply effective plane of measurement correction (shift) for native angle (not collapsed to gantry 0) VMAT QA with the widely used MatriXX Evolution and the recently released new MatriXX Resolution.

Materials and Methods