ESTRO 2021 Abstract Book

S689

ESTRO 2021

Conclusion Real-time assessment of DIBH breath hold quality via MV EPID image analysis has been successfully implemented. Results from the first patient demonstrated that the mean difference between the planned and observed LDs and SDs for some of the beams exceeded what would be expected given the tolerance of the monitoring tool. Both the quality of the breath hold and the patient positioning accuracy contribute to the observed differences. The results emphasize the potential of real-time assessment of DIBH using MV EPID imaging. This system will improve accuracy of DIBH treatments and possibly assist in improving the accuracy of patient positioning. PD-0856 Comparison of intrafraction motion when using two distinct systems to perform DIBH in lung SBRT. A. Prado Barragán 1 , D. Zucca Aparicio 2 , M.Á. De la Casa de Julian 2 , L. Alonso Iracheta 2 , J. Martí 3 , P. García de Acilu 2 , J. García 2 , P. Fernández Letón 1 HU HM Sanchinarro. HM Hopitales. , Medical physics and radiation protection, Madrid, Spain; 2 HU HM Sanchinarro. HM Hospitales, Medical physics and radiation protection, Madrid, Spain; 3 HU HM Sanchinarro. HM Hospitales, Medical physics and radiation protection, madrid, Spain Purpose or Objective In lung SBRT treatments high doses in few fractions are imparted to the tumor. Respiratory management systems are required to reduce target motion due to respiration. In this study intrafraction motion is estimated through intrafraction CBCT (Elekta Medical) when DIBH is performed using Active Breathing Coordinator (Elekta Medical) or Catalyst (CRad). Materials and Methods 190 patients with lung metastases were considered for DIBH-lung-SBRT treatments. For 120 of them the ABC systems was utilized and for the other 70 Catalyst was employed. 290 (550) CBCTs were recorded for Catalyst (ABC) patients. For every treatment session an intrafraction CBCT was synchronized with the first arc of the treatment, which was composed of two arcs. Patient position was corrected before the second arc was imparted. Using these corrections the intrafraction motion for each patient and treatment session was estimated.