Cone beam computed tomography for dose calculation quality assurance for magnetic resonance-only radiotherapy

• DOI: 10.1016/j.phro.2021.01.005
• Publication Date: 2021-02-03T17:25:34Z
• Authors: Jonathan J. Wyatt; Rachel A. Pearson; Christopher P. Wa...; Rachel L. Brooks; Karen Pilling; Hazel M. McCallum
• Keywords: Hounsfield scale; Image-guided radiation therapy

Magnetic Resonance (MR)-only prostate radiotherapy using synthetic Computed Tomography (sCT) algorithms with high dose accuracy has been clinically implemented. MR images can suffer from geometric distortions so Quality Assurance (QA) an independent, geometrically accurate, image could be required. The first-fraction Cone Beam CT (CBCT) demonstrated potential but not evaluated in a clinical MR-only pathway. This study the use of CBCT for QA radiotherapy.A total 49 patients treated were divided into two cohorts. Cohort 1 (20 patients) received back-up CT, whilst 2 (29 did not. All planned sCT and daily imaging MR-CBCT soft-tissue matching. Each was calibrated patient-specific stepwise Hounsfield Units-to-mass density curve. treatment plan recalculated on applied match doses compared. For rigidly registered to compared.Mean sCT-CBCT difference across both cohorts -0.6±0.1% (standard error mean, range -2.3%,2.3% ), 47/49 within [ -2%,1% ]. systematically lower than sCT-CT by -0.7±0.6% ( ±95% limits agreement). mean gamma pass rate 2%/2mm ) 96.1±0.4% 85.4%,99.7% ).CBCT-based appears feasible. There small systematic implying asymmetric tolerances ] would appropriate.