S1517
Interdisciplinary - Quality assurance and risk management
ESTRO 2026
Fodor 2 , Nadia Di Muzio 2,3 , Antonella del Vecchio 1 , Claudio Fiorino 1 1 Medical Physics, IRCCS San Raffaele Scientific Institute, Milano, Italy. 2 Radiation Oncology, IRCCS San Raffaele Scientific Institute, Milano, Italy. 3 Radiation Oncology, Vita Salute University, Milano, Italy Purpose/Objective: A one-day, single fraction treatment strategy for localized prostate cancer was clinically activated at our Institute since the end of 2023. The experience concerning the physics aspects of the entire procedure (planning, QA and delivery) was reviewed. Material/Methods: A Phase I-II trial exploring the feasibility to deliver 24 Gy in one fraction to prostate ± seminal vesicles (PTV) with a urethral sparing “HDR-like” approach was clinically implemented, using the Cyberknife (CK) system (Fig1). The entire procedure, including gold fiducial implants for delivery tracking, CT/MRI acquisition, contouring, planning, QA dosimetry and treatment, was planned to be performed in one single day. Data of the first 13 patients (Phase I part) were evaluated. Depending on the risk stratification, either prostate alone or prostate plus seminal vesicles were contoured, with application of a 2-3 mm margin to define PTV. A highly efficient plan-optimization template was tuned to meet requirements for PTV coverage, acceptable dose inhomogeneity, and predefined constraints for critical structures. (Fig2)., Upon plan approval, patient-specific QA (PSQA) included both punctual measurement and planar film dosimetry Tracking accuracy and efficiency were evaluated by analyzing live images acquired during delivery and estimating the residual error based on fiducial detection. Results: All patients completed the entire one-day procedure without delay. The average PTV coverage (excluding overlap with rectum/bladder/urethra) was 95% ±1 % was obtained, with a median value of 21% of the PTV receiving more than 36 Gy. For most patients, maximum dose constraints and dose-volume constraints were satisfied; minor deviations, accepted by the treating clinician, were reported in 3 pts for rectal mucosa and in 2 pts for bladder. A good agreement (mean deviation = 2.5 %, 1SD= 2.1, max deviation = 4.3 %) and satisfactory gamma analysis results (%>95% always >10/13 pts, 3%/2mm) were found. Concerning tracking accuracy, mean population deviations for the three main axes were within 0.2 mm; the worst axis (posterior-anterior) showed an overall SD of 0.54 mm, confirming the safety of the applied margins. The average treatment delivery time was approximately 45 minutes (range 36-60 minutes), mostly driven by the number of tracking images obtained during each session.
to-end imaging, planning and SABR delivery using anthropomorphic phantoms, and benchmark contouring and planning exercises (see Figure 2 below). The PI, supported by IRROG staff, approved benchmark cases and feedback was centrally coordinated through IRROG.On-study QA involved prospective review of the first patient enrolled at each site by the PI and IRROG team, with retrospective reviews planned for new dose level cohorts. Data management was led by Cancer Trials Ireland (CTI), who collaborated with IRROG to define electronic Case Report Form (eCRF) requirements, develop data validation checks, and ensure protocol compliance.
Results: Close collaboration between IRROG and CTI during eCRF design prompted protocol updates and an educational session where IRROG provided training on radiotherapy planning and data extraction. These efforts improved database design and enhanced detection of protocol deviations. Retrospective review of Dose Level 1 data identified the need for updated dose–volume constraints and additional eCRF validation checks, co-developed by IRROG physicists and CTI data managers, resulting in improved data quality and compliance. Conclusion: This initial experience demonstrated the technical and procedural value of a centralised RTQA system and highlighted the importance of cross-disciplinary collaboration in ensuring research study success. Lessons learned are now shaping four upcoming IISs, establishing a sustainable national radiotherapy research infrastructure. Keywords: National RTQA Programme Digital Poster Highlight 2379 Planning, patient QA and image-guidance aspects of single-fraction, one-Day robotic SBRT for localized prostate cancer. Sara Broggi 1 , Paola Mangili 1 , Carmen Gigliotti 1 , Roberta Castriconi 1 , Lucia Perna 1 , Alessia Tudda 1 , Andrei
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