S2372
Physics - Quality assurance and auditing
ESTRO 2026
Masturzo 6 , Eugenia Moretti 12 , Roberta Nigro 13 , Silvana Riccardi 13 , Serenella Russo 5 , Silvia Strolin 4 , Lidia Strigari 4 , Cinzia Talamonti 7 , Angela Vaiano 9 1 Medical Physics, ICTP, Trieste, Italy. 2 Medical Physics, AST Pesaro Urbino, Pesaro, Italy. 3 Medical Physics, Azienda Sanitaria USL Toscana Sud Est, Grosseto, Italy. 4 Medical Physics, Azienda Ospedaliero Universitaria di Bologna, Bologna, Italy. 5 Medical Physics, Azienda Sanitaria USL Toscana Centro, Firenze, Italy. 6 Medical Physics, Azienda Ospedaliero-Universitaria San Luigi Gonzaga, Orbassano, Italy. 7 Medical Physics, Azienda Ospedaliero Universitaria Careggi, Firenze, Italy. 8 Medical Physics, Azienda Unità Sanitaria di Reggio Emilia, Reggio Emilia, Italy. 9 Medical Physics, Azienda Sanitaria USL Toscana Centro, Pistoia, Italy. 10 Medical Physics, Azienda Ospedaliero Universitaria Pisana, Pisa, Italy. 11 Medical Physics, Fondazione Policlinico Universitario Agostino Gemelli, Roma, Italy. 12 Medical Physics, Azienda Sanitaria Universitaria Friuli Centrale, Udine, Italy. 13 Medical Physics, Azienda Unità Sanitaria Locale Rieti, Rieti, Italy Purpose/Objective: Electronic Portal Imaging Device (EPID)-based transit dosimetry has been used since the late 2000s for in vivo dose verification, improving treatment safety by detecting clinically significant errors before compromising efficacy. Despite widespread adoption, studies report limitations in dosimetric accuracy. To address this, an ESTRO working group published a standardized protocol for evaluating EPID dosimetry [1]. This multicenter study applies these guidelines to assess the performance of various EPID systems across institutions, software platforms, and TPS/linac combinations. Material/Methods: Twelve centers participated, using five EPID software solutions: Perfraction (n=7), Radcalc (n=2), Dosisoft (n=1), Softdiso (n=1), and Dosimetry Check (n=1). Perfraction uses a forward projection (FP) algorithm; others employ back projection (BP). Thirty-one beams were tested with 6 MV and 10 MV photons, with and without flattening filters (FFF). Measurements included homogeneous slab phantoms (10 cm, 30 cm) and inhomogeneous setups with 2 cm and 5 cm air gaps. Square fields of 2 × 2, 5 × 5, 10 × 10, and 20 × 20 cm ² were evaluated. Metrics included isocenter point dose differences and 2D gamma pass rates (GPR) in the coronal plane using global gamma criteria of 2%, 3%, and 5% dose difference with 2 mm distance-to- agreement. Results: In homogeneous phantoms, FP and BP algorithms showed similar point dose accuracy: FP averaged 0.3% (SD: 1.5%), BP 1.3% (SD: 2.4%). FP outperformed BP in dose distribution: GPR for FP was 97% (SD: 7%) at 2%/2mm, 99.8% (SD: 0.5%) at 3%/3mm, and 99.99%
before the project 67% of treatment plans were not verified, after implementation this percentage dropped to 8%, with only urgent cases excluded (Figure1). Importantly, despite dedicating 30 minutes of daily LINAC time to PSQA, no reduction in the number of patients treated was observed. This was likely because the PSQA time was absorbed during LINAC warm-up phases, while patient variability and equipment downtimes had a greater impact on throughput.
Conclusion: Applying Lean methodology enabled the redesign of the PSQA process, resulting in enhanced workflow efficiency, improved quality, and increased team engagement without reducing clinical capacity. Continuous monitoring of key indicators remains essential to sustain improvements and identify further optimization opportunities. This experience demonstrates that Lean principles can effectively support patient safety, operational sustainability, and staff empowerment in modern high-volume radiotherapy departments. Keywords: Lean methodology, Patient Specific QA
Proffered Paper 2941
Assessing the accuracy of EPID-based in vivo dosimetry algorithm in a multicentric context: a national study. Marco Esposito 1 , Riccardo Baldoni 2 , Antonietta Bartoli 3 , Francesca Bisello 4 , Andrea Bruschi 5 , Elisa Calamia 6 , Marta Casati 7 , Elisabetta Cagni 8 , Francesco Cesarini 2 , Alberto Ciarmatori 2 , Davidq Fedele 9 , Stefania Linsalata 10 , Matteo Galletto 11 , Francesca Greco 11 , Luigi
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