Cone beam CT verification for active breathing control (ABC)-gated radiotherapy for lung cancer AshleySue YeohKheng-Wei A. McNairHelen McDonaldFiona HawkinsMaria N. HansenVibeke RamosMonica FragkandreaIoanna BothwellSarah HerbertTrina TaylorHelen HelyerSarah BradaMichael 2014 Cone beam CT verification for active breathing control (ABC)-gated radiotherapy for lung cancer