ESTRO 2022 - Abstract Book

S420

Abstract book

ESTRO 2022

from first setup image to last treatment beam off. Treatment time was assessed as a function of MM, technique and number of CBCTs.

Figure 1: (a) Workflow for assessment of appropriate MM and (b) example ant-post fluoroscopy liver dome position

Results From September 2017 to September 2021, 145 patients underwent MM assessment. Of these, 67.6% were suitable for EBH, 20.0% for AC, 6.9% for gating and 5.5% FB. 88/100 patients assessed with fluoroscopy for liver dome consistency in EBH could achieve repeat EBH with <4mm variation. Reduction in liver motion with AC compared with FB was highly variable (mean 3.5 mm, range -0.3-16 mm). Treatment time was available for 613 fractions (Figure 2) and was largest for EBH (40 ± 14 min) and gated treatments (46 ± 19 min), compared with AC (32 ± 11 min, p<0.001) and FB (27 ± 12 min, p<0.001). Treatment time was independent of fraction size. Four patients originally assessed as suitable for EBH could not achieve reproducible EBH at treatment and were treated in FB (3) or with AC (1). Arc treatments were quicker than static gantry treatments (35 ± 14 min vs 43 ± 15 min, p = <0.001). Average treatment time was increased by 7 mins with each CBCT acquired.

Figure 2: Treatment time per fraction as a function of motion management approach

Conclusion MM in liver SBRT must be assessed per-patient to determine the most appropriate technique for that patient. Extended treatment times must be taken into account when deciding on optimal MM strategy. Methods to reduce intra-fraction volumetric imaging, such as real-time imaging or tracking, may be beneficial to reduce treatment time.

MO-0472 Limitations of phase-sorting based pencil beam 4D proton dose calculation under irregular motion

A. Duetschler 1,2 , J. Prendi 1,3 , S. Safai 1 , D.C. Weber 1,4,5 , A.J. Lomax 1,2 , Y. Zhang 1

1 Paul Scherrer Institute, Center for Proton Therapy, Villigen PSI, Switzerland; 2 ETH Zurich, Department of Physics, Zurich, Switzerland; 3 University of Basel, Department of Physics, Basel, Switzerland; 4 University Hospital of Zurich, Department of Radiation Oncology, Zurich, Switzerland; 5 University of Bern, Department of Radiation Oncology, Bern, Switzerland

Purpose or Objective