ESTRO 2022 - Abstract Book

S419

Abstract book

ESTRO 2022

Figure 2A shows examples of the CBCT-based tumor template and 2B shows the tumor-enhanced cine MV image with the segmented tumor position. In this case, the internal tumor shift in the patient between setup CBCT and treatment delivery was 2.9 mm in the cranial direction. Figure 2C shows the tumor shift at all imaged fractions for this patient. The mean shift was 3.4 mm (SD = 2.1 mm). Conclusion A method for markerless lung tumor localization in cine MV images was developed and applied to determine the intrafraction tumor shift between setup imaging and treatment delivery in lung cancer DIBH IMRT treatments. The method is well-suited for DIBH treatments, where the optimally small residual lung tumor motion during IMRT field delivery allows generation of a composite cine MV image from the IMRT segments.

MO-0471 Motion management in liver SBRT and its impact on treatment time

N. Hardcastle 1 , M. Gaudreault 1 , A. Yeo 1 , E. Ungureanu 1 , R. Barnes 2 , C. Markham 2 , S. Chander 3 , J. Chu 3

1 Peter MacCallum Cancer Centre, Physical Sciences, Melbourne, Australia; 2 Peter MacCallum Cancer Centre, Radiation Therapy, Melbourne, Australia; 3 Peter MacCallum Cancer Centre, Department of Radiation Oncology, Melbourne, Australia Purpose or Objective Reduction of respiratory motion is critical in liver stereotactic body radiotherapy (SBRT) to reduce organ at risk dose, facilitating increased tumour dose and resultant local control. In our institution we assess all liver SBRT patients prior to simulation to determine appropriate motion management (MM). This retrospective review aims to evaluate the patterns of use of MM techniques and their impact on treatment time. Materials and Methods For each patient we assess suitability, in order of priority, of voluntary exhale breath hold (EBH), free breathing gating, abdominal compression (AC), or free breathing (FB), according to the flowchart in Figure 1. We use an external surrogate to assess breath hold capability, followed by anterior-posterior fluoroscopy to assess liver dome position consistency. From MM assessment session records, we extracted liver dome position consistency in repeat EBHs, liver dome motion change with AC and decision of MM used for simulation and treatment. All patients were treated on a TrueBeam linear accelerator with flattening-filter free photon beams using arc (VMAT) or static gantry (3DCRT, IMRT) techniques, with between 6 and 20 Gy per fraction. CBCT image guidance was used in all cases, with acquisition matched to the MM technique (free breathing, gated or breath hold CBCT). From the record and verify system we extracted treatment time, defined as time