ESTRO 2023 - Abstract Book

S1603

Digital Posters

ESTRO 2023

The three planning approaches result in similar CTV coverage with respect to V95%. However, combining two optimization function types for the OAR, as in plan_3, resulted in a lower mean dose over all the treatment fractions combined. Additional time spent on multiple plans on the pCT can benefit online plan adaptation by saving time during treatment and reducing OAR doses.

PO-1862 Tracking irregular breathing with pencil beam proton therapy

A.C. Giovannelli 1,2 , S. Safai 1 , D. Meer 1 , D.C. Weber 1,3,4 , A.J. Lomax 1,5 , G. Fattori 1

1 Paul Scherrer Institut, Center for Proton Therapy, Villigen, Switzerland; 2 ETH Zürich, Department of Physics, Zürich, Switzerland; 3 University Hospital of Zürich, Radiation Oncology Department, Zürich, Switzerland; 4 Inselspital, Bern University Hospital, University of Bern, Radiation Oncology Department, Bern, Switzerland; 5 ETH Zürich, Department of Physics, Zürich, Switzerland Purpose or Objective Respiratory synchronized tracking has recently been introduced as an option to track tumor motion with proton beams. The effectiveness of this technique, which includes the preparation of a template tracking plan based on the motion extracted from the planning 4DCT, is however challenged by the intra- and inter-fraction respiratory variations. Our aim is therefore to test the limits of this approach with respect to irregular breathing patterns. We do so by taking into account the current capabilities of proton units and exploring their potential in the perspective of next-generation solutions, which may allow for larger momentum acceptance. Materials and Methods Tumor tracking was simulated for the treatment of 6 NSCLC patients selected from a database including 5xrepeated 4DCT imaging. Single-field plans were optimized on the mid-position image of the first 4DCT and the individual phases used for template planning, which includes the pre-computation of pencil beam lateral offsets for tracking and resorting by descending energy, which are then delivered in synchrony with the patient’s breathing. The remaining four 4DCT sets were combined via deformable image registration into a multi-breath imaging dataset for simulating treatments including breathing variability. Incremental tracking offsets required to compensate for motion variability were calculated and 4D dose calculations performed to assess CTV coverage (V95) and dose homogeneity (D5-D95) assuming conventional (±0.6% dp/p) and unconstrained momentum acceptance of the gantry beam line.