3 years ago

Credentialing of vertebral stereotactic ablative body radiotherapy in a multi-centre trial

Nicholas Hardcastle, Tomas Kron, Olivia Cook, Joerg Lehmann, Paul L.R. Mitchell, Shankar Siva
16 out of 18 centres delivered spatially and dosimetrically accurate vertebral SABR. Incorrect planning system MLC specification in one centre was detected. Cord-target dose gradient was delivered as planned, independent of delivery or planning modality. Dosimetric audits are a fundamental component of vertebral SABR. Stereotactic ablative body radiotherapy (SABR) in multi-centre trials requires rigorous quality assurance to ensure safe and consistent treatment for all trial participants. We report results of vertebral SABR dosimetry credentialing for the ALTG/TROG NIVORAD trial. Centres with a previous SABR site visit performed axial film measurement of the benchmarking vertebral plan in a local phantom and submitted radiochromic film images for analysis. Remaining centres had on-site review of SABR processes and axial film measurement of the vertebral benchmarking plan. Films were analysed for dosimetric and positional accuracy: gamma analysis (>90% passing 2%/2mm/10% threshold) and ≤ 1 mm positional accuracy at target-cord interface was required. 19 centres were credentialed; 11 had on-site measurement. Delivery devices included linear accelerator, TomoTherapy and CyberKnife systems. Five centres did not achieve 90% gamma passing rate. Of these, three were out of tolerance (OOT) in low (<5Gy) dose regions and > 80% passing rate and deemed acceptable. Two were OOT over the full dose range: one elected not to remeasure; the other also had positional discrepancy greater than 1 mm and repeat measurement with a new plan was in tolerance. The original OOT was attributed to inappropriate MLC constraints. All centres delivered planned target-cord dose gradient within 1 mm. Credentialing measurements for vertebral SABR in a multi-centre trial showed although the majority of centres delivered accurate vertebral SABR, there is high value in independent audit measurements. One centre with inappropriate MLC settings was detected, which may have resulted in delivery of clinically unacceptable vertebral SABR plans.

Publisher URL: https://www.sciencedirect.com/science/article/pii/S1120179720300594

DOI: 10.1016/j.ejmp.2020.03.004

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