Dosimetric impact of 4DCT artifact in carbon-ion scanning beam treatment: Worst case analysis in lung and liver treatments

Introduction: We evaluated the impact of 4DCT artifacts on carbon-ion pencil beam scanning dose distributions in lung and liver treatment. Methods & materials: 4DCT was performed in 20 liver and lung patients using area-detector CT (original 4DCT). 4DCT acquisition by multi-detector row CT was simulated using original 4DCT by selecting other phases randomly (plus/minus 20% phases). Since tumor position can move over the respiratory range in original 4DCT, mid-exhalation was set as reference phase. Total prescribed dose of 60 Gy (RBE) was delivered to the clinical target volume (CTV). Reference dose distribution was calculated with the original CT, and actual dose distributions were calculated with treatment planning parameters optimized using the simulated CT (simulated dose). Dose distribution was calculated by substituting these parameters into the original CT. Results: For liver cases, CTV-D95 and CTV-Dmin values for the reference dose were 97.6 +/- 0.5% and 89.8 +/- 0.6% of prescribed dose, respectively. Values for the simulated dose were significantly degraded, to 88.6 +/- 14.0% and 46.3 +/- 26.7%, respectively. Dose assessment results for lung cases were 84.8 +/- 12.8% and 58.0 +/- 24.5% for the simulated dose, showing significant degradation over the reference dose of 95.1 +/- 1.5% and 87.0 +/- 2.2%, respectively. Conclusions: 4DCT image quality should be closely checked to minimize degradation of dose conformation due to 4DCT artifacts. Medical staff should pay particular attention to checking the quality of 4DCT images as a function of respiratory phase, because it is difficult to recognize 4DCT artifact on a single phase in some cases (C) 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.