S2410
Physics - Quality assurance and auditing
ESTRO 2026
Nine audits were completed in full, encompassing 5 systems for collecting external respiratory signal at CT and 4 linac gating/motion management systems (Table 1). Measurements covered all techniques except tumour tracking, and 50 cases were measured in total. Gamma passing rates (4%/2 mm, globally normalised, 10% low dose threshold) ranged from <40% to 100%. The additional dosimetry and spatial metrics enabled low gamma passing rates to be attributed to specific failure modes, such as IGRT errors or inaccurate dose calculation (Figure 1).
Proffered Paper 5139
Treatment quality benchmarking for complicated and varied clinical workflows – preliminary results from the ACDS dosimetry audit for motion management Alex Burton 1,2 , Sabeena Beveridge 1,2 , Andrew Alves 1 , Nick Hardcastle 2,3 , Rick Franich 4 1 Australian Clinical Dosimetry Service, Australian Radiation Protection and Nuclear Safety Agency, Yallambie, Australia. 2 Department of Physical Sciences, Peter MacCallum Cancer Centre, Melbourne, Australia. 3 Centre for Medical Radiation Physics, University of Wollongong, Wollongong, Australia. 4 School of Science, RMIT University, Melbourne, Australia Purpose/Objective: Clinical workflows for implementing respiratory motion management are varied and technically challenging (1). Errors or uncertainties may be introduced at any stage along the treatment chain, influenced by both the treatment site and choice of motion management technique (2, 3). Here, we present the preliminary results of an end-to-end dosimetry audit implemented on a national scale, designed to encompass a broad range of clinical workflows for different motion management techniques. Material/Methods: The audit was trialled at 10 facilities. Participating facilities were required to conduct planning CTs, contouring, treatment planning, image guidance and treatment delivery with the phantom, per local protocols. Dosimetry measurements were conducted using radiochromic film.The phantom contains 2 SBRT treatment sites (thorax/lung and abdomen/liver) and is compatible with 6 motion management techniques (ITV, Mid-ventilation, DIBH, EEBH, free-breathing gating, tumour tracking). An audit case combined treatment site and motion management technique (12 possible combinations), using initials as identifiers (e.g. thoracic SBRT using the ITV technique referred to as case T-I).Dosimetry measurements were compared to the facility’s planned dose distributions using gamma analysis. Additionally, spatial errors were quantified by comparing the centres off mass of the 75% isodose lines in the planned and measured dose distributions (2D distance-to-agreement (DTA)). Dosimetric errors were quantified by examining the average dose within a region of interest (ROI) on the film corresponding to the known location of the PTV. The average dose in this ROI was compared to the average PTV dose in the corresponding 2D planned dose plane ( Δ D). Finally, the impact of any spatial errors was removed from this comparison by offsetting the film PTV ROI by the 2D DTA ( Δ Dcorr). Results:
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