ESTRO 2025 - Abstract Book

S3682

Physics - Quality assurance and auditing

ESTRO 2025

Switzerland. 10 Luxemburg Health Directorate, Luxemburg Health Directorate, Luxemburg, Luxembourg. 11 Inselspital, Bern University Hospital and University of Bern, Bern, Germany. 12 University Hospital Basel, University Hospital Basel, Basel, Switzerland. 13 Städtisches Klinikum Dresden, Städtisches Klinikum Dresden, Dresden, Germany. 14 Geneva University Hospital, Geneva University Hospital, Geneva, Switzerland. 15 University Hospital of Modena, University Hospital of Modena, Modena, Italy. 16 Kantonsspital Graubunden, Kantonsspital Graubunden, Chur, Switzerland. 17 Hirslanden Clinic, Hirslanden Clinic, Zurich, Switzerland. 18 University Hospital Zurich, University Hospital Zurich, Zurich, Switzerland. 19 Kantonsspital Winterthur, Kantonsspital Winterthur, Winterthur, Switzerland. 20 University of Zurich, University of Zurich, Zurich, Switzerland Purpose/Objective: The primary aim of this study is to quantify contouring variations and to provide a detailed description of quality assurance measures that can ensure protocol compliance related to dosimetry and treatment delivery. Material/Methods: This analysis is based on the randomized DOSIS RCT trial for patients with painful vertebral metastases. Quality assurance (QA) analysis involved two components. First, treatment planning data from 31 patients treated with SBRT were reviewed for a retrospective evaluation of contouring practices. Six experts in spine stereotactic body radiotherapy (SBRT) assessed critical structures, including the gross tumor volume (GTV), clinical target volume (CTV), high-dose planning target volume (PTV), low-dose PTV, spinal cord, and cauda equina as organs at risk (OAR), following trial guidelines. Compliance with segmentation-protocols was documented, categorizing contours into protocol-conform, acceptable variation, and unacceptable variation. The second component focused on evaluating dosimetric outcomes and treatment delivery. Key objectives included achieving a V100 ≥ 80% and ensuring that the spinal cord PRV Dmax remains <23.8 Gy to 0.1 cm³ for five fractions and <35 Gy to 0.1 cm³ for 10 fractions, while the cauda equina Dmax stays respectively <25 Gy to 0.1 cm³ and <37.5 Gy to 0.1 cm³. Compliance with normal tissue constraints was recorded, and a qualitative analysis identified differences in protocol adherence. Results: A total of 31 cases were analysed for radiotherapy quality assurance (QA) review. GTV compliance was observed in 27 out of 31 cases (87%), while high-dose PTV compliance was noted in 24 out of 31 cases (77.4%). For organs at risk (OAR), compliance for the cauda equina was achieved in only 3 out of 12 contours (25%). Spinal cord delineation compliance was significantly higher at 85%.The QA process achieved 100% compliance with all mandatory trial protocol requirements for all OARs as defined by the DVH parameters (Figure 1). For the high-dose PTV, V100 ≥80% compliance was met for the regimen of 40 Gy in five fractions and for 48.5 Gy in 10 fractions, in 12 out of 18 patients (66%) and 8 out of 13 patients (62%), respectively. Additionally, there was 100% compliance for V95 ≥ 95% for both dose regimens for the low-dose PTV.