ESTRO 2025 - Abstract Book

S2802

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

Conclusion: Automatically generated VMAT plans for liver SBRT at an Ethos had improved PTV coverage compared to clinical Cyberknife plans, with overall similar quality for the OARs. With daily adaptive planning at an Ethos to mitigate inter fraction anatomy changes, VMAT plan dosimetry can be further improved. With the developed workflow we have demonstrated that a transfer from CyberKnife to Ethos ART for liver SBRT is dosimetrically safe and most likely beneficial for patients.

Keywords: CyberKnife, Ethos-VMAT, automated planning

References: 1.

Breedveld, S., Storchi, P. R., Voet, P. W., & Heijmen, B. J. (2012). iCycle: Integrated, multicriterial beam angle, and profile optimization for generation of coplanar and noncoplanar IMRT plans. Medical physics, 39(2), 951–963. https://doi.org/10.1118/1.3676689

2071

Digital Poster Impact of Carbon-Fiber-Reinforced Polyetheretherketone (CFR-PEEK) Constructs in Spine Stereotactic Radiosurgery (SRS) Lauren Weinstein, Matthew Skinner Radiation Oncology, Kaiser Permanente, South San Francisco, USA Purpose/Objective: Spine SRS success is dependent upon high quality imaging and accurate dosimetric calculations, aspects that can be compromised by using titanium stabilization hardware. Recently, radiolucent CFR-PEEK has emerged as an alternative to titanium due to superior imaging attributes and reduced dose perturbations. We assessed the dosimetric impact of titanium and CFR-PEEK constructs compared to normal bone using an anthropomorphic spine phantom with multiple, commercially available, advanced dose calculation algorithms. Material/Methods: A customized thorax phantom containing interchangeable spine inserts of bone, bone with titanium construct, or bone with a CFR-PEEK construct was CT simulated with iterative metal artifact reduction (iMAR) techniques, to assess image quality differences between native bone and the different constructs. 55 SRS plans were created for each of the three spine inserts, using Varian Eclipse 16.1 and Brainlab Elements 3.0 and 4.0, four dose calculation algorithms, AAA, AcurosXB from Varian and Pencil Beam and Monte Carlo from Brainlab and two photon energies, 6FFF and 10FFF. Target volumes were created to mimic typical clinical cases that treated the vertebral body with maximum sparing of the spinal cord. Plans were delivered on a Varian Truebeam linear accelerator using Brainlab ExacTrac for image guidance. Measured versus calculated dose distributions were compared using radiochromic film. Results: Titanium constructs showed pronounced image artifacts compared to bone or CFR-PEEK, some of which were reduced with DECT and MAR. CFR-PEEK had superior canal visualization and greatly reduced image artifacts visible, with further reduction observed when using dual-energy CT and iMAR. Film analysis of titanium insert dose distributions showed errors of 15 to 20% between the TPS within 5 mm of the construct hardware. The absence of metal in the majority of the CFR-PEEK construct resulted in films that agreed closely with the TPS and were comparable to measurements in native bone. Distant from the implanted hardware and along the spinal cord itself, all TPS algorithms agreed within 5% or better to film in bone, titanium and CFR-PEEK.