Session Item

A radiotherapy quality assurance (QA) program was developed as part of a national plan for the expansion of lung stereotactic ablative body radiotherapy (SABR) services. The aim was to ensure consistent, high-quality SABR was implemented across all centres introducing this technique. As part of the QA program, radiation oncologists’ ability to delineate target volumes and associated organs at risk (OARs), according to UK SABR Consortium Guidelines and Global Harmonization Group Consensus Guidelines (Mir et al, 2020), was assessed.

A contouring benchmark case was circulated amongst 24 centres starting their lung SABR program. The 4DCT dataset sent contained 12 individual phases. A diagnostic PET-CT was also provided. Two clinicians from each hospital were invited to contour the ITV, PTV and 10 OARs following supplied guidance. All submissions were reviewed by a team of SABR experts comprising 5 radiation oncologists, a medical physicist and a clinical research fellow. Detailed feedback was provided through standardised written and pictorial reports and any unacceptable contours were asked to be resubmitted after further guidance from experienced mentors assigned through the implementation program.

Consensus volumes were agreed by all reviewers. Acceptability criteria were defined for each structure based on cranio-caudal borders, axial under or over-contouring and inclusion/exclusion of anatomical features as detailed in the instructions.

44 radiation oncologists completed the benchmark case, only one was approved on the first attempt. Failed submissions had a median of 6 unacceptable structures (range 2-9). 52.3% of ITVs were found to be unacceptable, mostly due to under-contouring, however most PTVs (95.5%) had been grown correctly. 6/10 OARs had failure rates ≥50%, the brachial plexus being the most complex structure to contour. Failure rates and the most common reasons for structures being unacceptable are detailed in Table 1.

40/43 resubmissions were approved, with those still unacceptable being referred to one of the 5 radiation oncologist SABR experts for further training.

The outlining benchmark case has highlighted training needs in delineation and interpretation of guidelines. Visual aids may prove useful in future guidance. Detailed feedback was provided to aid with education and ongoing support from mentors is in place. Contouring workshops have also been developed and participation in peer review and clinical trials is recommended going forward.