The feasibility of direct treatment planning via contrast-enhanced computed tomography: an evaluation of dose differences based on the dimensional dose distribution comparison method

Background: We used a MapCHECK software-based dimensional dose distribution comparison method capable of evaluating point-to-point geometrical dose differences in volume to determine whether doses obtained from an enhanced computed tomography (CT)-based treatment plan, which better defines the target regions and organs at risk, differs from doses obtained from plain CT and then evaluated the feasibility of treatment planning via enhanced CT. Materials and Methods: Forty-three randomly selected patients underwent plain and subsequent enhanced CT with the same settings. Treatment plans developed for the two scans were identical in terms of planning parameters (e.g., isocentre, gantry angle, segments) and monitor units (MU) used for dose calculation. Horizontal and vertical dose distribution planes across the same isocentre were selected from two types of plan; a two-dimensional dose distribution analysis was used to determine the Distance-To-Agree (DTA) pass ratios of corresponding dose distribution planes. Results: Obtained doses at the head and neck (H&N) and pelvic sites did not differ greatly between enhanced and plain CT. However, enhanced CT significantly influenced doses to the lower thoracic oesophagus. A corrected pass ratio that was achieved by non-pass points in lower isodose areas excluded from the statistical analysis had better clinical outcome. Conclusion: Radiation plans with multi-fields and multi-angles can reduce the influence of enhanced CT on torso cases and may even negate its influence on H&N cases. Enhanced CT can be directly used for planning unless the target region contains the lower oesophagus and its surrounding blood vessel whose high density requires correction.