Radiotherapy Plan Quality Assurance in the ABC-07 Trial of Stereotactic Body Radiotherapy for Locally Advanced...

The ABC-07 phase II randomised controlled trial (ISRCTN: 10639376) investigated the addition of stereotactic body radiotherapy (SBRT) to systemic chemotherapy in locally advanced biliary tract cancers (BTCs). We report the radiotherapy quality assurance (RTQA) of SBRT treatment plans in the trial.

RTQA was performed before and during accrual, including benchmark contouring and planning cases, along with prospective independent case review (ICR) of the first three patients from each centre randomised to SBRT. Prescription doses were up to 50 Gy in 5 fractions or up to 67.5 Gy in 15 fractions. Cases were reviewed for segmentation accuracy and plan quality, including target coverage and organ-at-risk (OAR) constraints being met.

Benchmark cases: Six of seventeen contouring submissions required revision (35%), and 6/17 planning submissions were revised after feedback on what was achievable by other centres. Prospective ICR: Thirty-one of forty-one cases from all 12 recruiting centres that were randomised to SBRT underwent review in real-time, and the others were reviewed retrospectively. Eight of these prospectively reviewed cases required revisions during the review process (26%, including 7 contouring and 2 planning revisions). Nineteen of forty-one plans overall (46%) had deviations from trial protocol objectives (even after any revisions), mostly unavoidable target coverage compromise (D95% < 90%) because of proximal OARs such as duodenum (17/41) and stomach (6/41).

Despite rigorous plan QA, we encountered variability in segmentation and plan coverage. The revision rate was reduced between pre-trial and on-trial cases. Radiotherapy doses in the protocol were achievable in many cases; however, target coverage was frequently compromised to maintain OAR dose constraints. Such compromises should be prespecified in future studies.