ESTRO 2021 Abstract Book

S1471

ESTRO 2021

Figure 1. Experimental setup.

Results A total of 22 4DCT datasets for lung cancer subjects were acquired for this study. The same treatment plan was delivered for each of the patient motion traces (47 s gantry period, 6 kV imaging angles). Motion characteristics and tracking results are shown in Table 1. Successful tracking was observed for all preliminary cases, as shown in Figure 2 and by the maximum δ rms of 1.0 mm. The preliminary work confirms the vendor specifications that RMS tracking errors are less than 1.5 mm. Further tracking and margin analysis will be performed by investigating the correlation between tracking accuracies and motion parameters (imaging frequency, target motion ellipticity/hysteresis, miscorrelation between internal and external motion, and chest motion amplitude). Table 1. 3D target and 1D chest motion statistics and tracking errors for the 22 preliminary cases. Target motion (mm) Chest motion (mm) δ rms (mm) δ rms_adj (mm) Mean 16.0 9.1 0.8 0.4 Min 5.1 3.5 0.6 0.3 Max 30.3 18.7 1.0 0.6

Figure 2. Examples of a regular and an irregular respiratory pattern and resulting tracking.

Conclusion A workflow for performing patient specific measurements for these treatments has been developed and demonstrated. The preliminary work indicates that when internal and external motion are correlated, a 1.5 mm margin is sufficient to cover uncertainties in target position due to tracking. PO-1748 SGRT quality assurance for stereotactic treatments R. Rodríguez Romero 1 , A. López Corella 1 , M. Torres López 1 , M. Pinto Monedero 1 , P. Sánchez Rubio 1 , J. Martínez Ortega 1 1 Hospital Universitario Puerta de Hierro Majadahonda, Servicio de Radiofísica y Protección Radiológica, Majadahonda, Spain