S2376
Physics - Quality assurance and auditing
ESTRO 2026
anatomical classification alone does not reliably reflect plan complexity, whereas MD provides a more accurate descriptor. A weak decreasing trend in global GPR with increasing MD was found.
die-overzicht/rt-hype/, Nov 11 2025.[4] H. Dob š í č ek Trefná et al., Strahlentherapie und Onkologie, vol. 193, no. 5, pp. 351-366, 2017/05/01 2017.[5] P. Shrivastava et al., Int J Radiat Oncol Biol Phys, vol. 16, no. 3, pp. 571-87, Mar 1989. Keywords: hyperthermia, superficial, harmonization Digital Poster 3222 A tools to manage plan complexity in treatment planning system: Modulation Degree as a predictive metric on pre-treatment patient-specific QA outcome Laura Ceccarelli 1 , Sebastiano Paolucci 1 , Andrea Bruschi 2 , Alessandro Ghirelli 2 , Silvia Pini 2 , Claudia Poggiali 2 , Edoardo Salmeri 3 , Roberto Pellegrini 3 , Serenella Russo 2 1 Department of Experimental and Clinical Biomedical Sciences “M. Serio”, University of Florence, Florence, Italy. 2 Medical Physics Unit Florence-Empoli, Department of Hospitals Network, Azienda USL Toscana Centro, Florence, Italy. 3 Clinical Research – Medical Affairs, Elekta AB, Stockholm, Sweden Purpose/Objective: This study evaluates whether the Modulation Degree (MD), a plan - complexity metric provided by the Monaco TPS, can predict patient-specific pre- treatment QA outcomes and support complexity management during the planning stage. Material/Methods: A total of 128 Volumetric Modulated Arc Therapy VMAT treatment plans were analyzed, covering head and neck, whole and partial breast, head and chest sites. All plans were generated with Elekta Monaco TPS (version 6.1) using a 2 mm calculation grid and delivered with 6 MV photon beams on an Elekta Versa HD linac. MD was available during planning process to quantify plan modulation by assessing segment areas and monitor units. Patient-specific QA verifications were performed using the PTW Octavius 4D phantom and Octavius Detector 1500 with 3D dose reconstruction. Gamma analysis was conducted with global 3%/2 mm as well as local 3%/3 mm criteria by adopting 10% dose threshold. Process stability was first assessed per anatomical site through I-charts to derive local Lower Control Limits (LCLs) (Ref.1) and Lower Action Limits (LALs) (Ref.1). A second analysis considered plan complexity instead of anatomical site: all plans were ordered by increasing MD and grouped using the shifting-range method to calculate MD- dependent Statistical Process Control (SPC) limits (Ref.1). Results: A substantial overlap of MD values was observed across anatomical sites (Fig.1), indicating that
The MD-based SPC analysis produced decreasing LCL/LAL values with increasing MD, resulting in stricter thresholds for low-complexity plans and more permissive limits for highly modulated plans (Fig.2). This behavior suggests that MD-based grouping better reflects the intrinsic variability and expected performance of plans with different modulation levels.
Conclusion: MD emerged as a more effective descriptor of plan delivery complexity than anatomical site. MD-based SPC thresholds improved the robustness and representativeness of patient-specific QA by avoiding excessive strictness for complex plans and excessive permissiveness for simple plans. MD proved to be a useful tool to manage plan complexity during planning process.Future work will extend the dataset by enlarging the data sample and including other beam energies. References: 1. AAPM Task Group 218.Tolerance Limits and Methodologies for IMRT Measurement-Based Verification QA: Recommendations of AAPM Task Group No.218.Med Phys.2018;45(4):e53-e83 DOI:10.1002/mp.12810. Keywords: Modulation Degree, LALs, LCLs
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