Conventional margins not sufficient for post-prostatectomy prostate bed coverage: An analysis of 477 cone-beam computed tomography scans

Abstract

Purpose To study prostate bed deformation, and compare coverage by 5 mm and 10 mm posterior expansion PTV margins. Method Fifty patients who completed post-prostatectomy radiotherapy had two expansion margins applied to the planning CT CTV: PTV10 (10 mm isometrically) and PTV5 (5 mm posteriorly, 10 mm all other directions). The CTV was then contoured on 477 pre-treatment CBCTs, and PTV5 and PTV10 coverage of each CBCT-CTVs was assessed. The maximum distance from the planning CT CTV to the combined CTV of all CBCTs including the planning CT CTV was measured for the superior part of the prostate bed, and the inferior part of the prostate bed, for every patient. Results The mean difference betw..