ESTRO 2023 - Abstract Book

S1555

Digital Posters

ESTRO 2023

Results No significant dose delivery differences were identified (< 1%) with a single layer of activated TachoSil (approximately 1 mm thick). When the used in two layers, a 25% reduction in absorption was found. The combination of TachoSil and single layer Tabotamp (300 µ m) did not attenuate significantly the absorption rates (< 2%). Conclusion During brain IORT, employing surgical hemostatic patches should be carefully regarded. Intraoperative imaging could help ease a real-time assessment of applicator-tissue contact and online Monte Carlo planning.

PO-1825 PRIMO Monte Carlo software as a tool for commissionning of a treatment planning system

J. Calvo-Ortega 1,2 , M. Hermida-López 3

1 Hospital Quirónsalud Barcelona, Radiation Oncology, Barcelona, Spain; 2 Hospital Quirónsalud Málaga, Radiation Oncology, Málaga, Spain; 3 Hospital Universitari Vall d’Hebron, Servei de Física i Protecció Radiològica, Barcelona, Spain Purpose or Objective The AAPM Medical Physics Practice Guideline 5.a recommends checking the dose calculation accuracy of clinical plans during the commissioning of a treatment planning system (TPS). This study aims to assess the feasibility of the freely available PRIMO Monte Carlo (MC) software (https://www.primoproject.net/) to verify the dose distributions of clinical plans and compare the results with measurements performed with an ionization chamber array and portal dosimetry. Materials and Methods The Acuros XB v. 16.1 algorithm of the Eclipse TPS was configured for 6 MV flattening-filtered photon beams, from a TrueBeam linac equipped with a High Definition MLC. PRIMO v. 0.3.64.1814 MC simulation software was used with the phase space files (version 2, Feb. 27, 2013) provided by Varian for TrueBeam 6 MV beams. PRIMO was used with the Dose Planning Method (DPM) simulation engine, and it was benchmarked against the reference dosimetry dataset published by the Imaging and Radiation Oncology Core–Houston (IROC-H, Med Phys. 2016 May;43(5):2374). The dosimetric parameters checked were the following: percentage depth–doses (PDDs), 40 × 40 cm2 off–axis ratios (OARs), open–field output factors (OFs) at the depth of the maximum dose (Dmax), and OF for IMRT–style and SBRT–style fields, both at a depth of 10 cm. Thirty clinical plans (10 IMRT, 20 VMAT) were calculated with the Acuros XB model (dose to medium) and verified in three independent ways: 1) the PTW Octavius 4D (O4D) phantom in conjunction with the PTW 1600 SRS detector, 2) the Varian Portal Dosimetry system and 3) the PRIMO software. The first two methods do not take into account the real anatomy of the patient, while the PRIMO-based verification does not include the plan delivery. For the methods 1) and 3), evaluation of the Eclipse dose calculations was performed using a 3D gamma index analysis. For the portal dosimetry verification, a 2D gamma index analysis was done. The 3% global/2 mm (dose threshold of 10%) criteria recommended by the AAPM TG 218 report was used with the three verification methods. For the PRIMO-based verification, the gamma evaluation was performed for the whole patient (“body”) and the planning target volume (PTV). Results 1. PDDs, 40 × 40 cm2 OARs, open–field OFs and OFs for IMRT–style and SBRT–style fields obtained from the PRIMO simulations had good agreement with the benchmark IROC-H data (see table). The highest difference of 2.0% was found for the 2x2 cm2 SBRT–style OF. 2. Gamma passing rates (GPRs) of 99.4% ± 0.6% and 99.9% ± 0.3% were obtained for the O4D (PTW1600) and portal dosimetry methods, respectively. For the PRIMO-based verification, GPRs of 99.5% ± 0.6% and 99.5% ± 1.2% were found for