ESTRO 2023 - Abstract Book

S294

Sunday 14 May 2023

ESTRO 2023

Conclusion Adequate coverage of the lymph node CTV levels L1-2 and L3-4 can be obtained using robust optimization based on {5mm/3%} setup and range uncertainties without additional PTV margins to compensate for larger setup uncertainties in these regions.

MO-0393 VMAT-based prostate radiotherapy treatment using online triggered imaging (TI) L. Nguyen 1 , T. Vu 1 1 GenesisCare, Radiation Therapy, Melbourne, Australia

Purpose or Objective To investigate the feasibility and dosimetric effect of real-time TI for prostate cancer patients receiving volumetric modulated arc therapy (VMAT) based radiotherapy treatment. Materials and Methods Fifteen patients were previously treated with VMAT-based radiotherapy (78Gy/39 fractions or 60Gy/20 fractions). TI is an online, real-time image verification technique used on prostate cancer patients with 3 fiducial markers. The Varian Truebeam’s built-in program automatically detects the 3 fiducial markers during the single arc delivery, with a ‘traffic light’ system being followed at each 15-second interval image capture (Figure 1). For the cases in the red category, the magnitude and directions of the couch shift were recorded to investigate the dosimetric impact of TI. This retrospective dosimetric analysis simulated non-TI prostate radiotherapy treatment. A duplicate plan for each of these patients was created in the Eclipse planning system, and the recorded shifts were applied in the opposite direction (anterior vs posterior, left vs right, superior vs inferior) and then calculated. To evaluate the dosimetric effect of TI, target metrics for the clinical target volume (CTV) D98% ≥ 98% and planned target volume (PTV) D98% ≥ 95% were compared between the deliverable plan which is represented by TI, and non-TI plan had the shifts not been applied. To evaluate the time taken for TI radiotherapy versus non-TI, each patient’s treatment was timed from the initial set-up for TI until complete beam deliverance. This time was compared against the time taken for a non-TI cohort group of 15 prostate cancer patients using the TrueBeam Varian system.