Novel Simulation for Dosimetry Impact of Diaphragm Respiratory Motion in Four-Dimensional Volumetric Modulated Arc Therapy for Esophageal Cancer.

Background and purpose: The diaphragm respiratory motion (RM) could impact the target dose robustness in the lower esophageal cancer (EC). We aimed to develop a framework evaluating the impact of different RM patterns quantitatively in one patient, by creating virtual four-dimensional computedtomography (v4DCT) images, which could lead to tailored treatment for the breathing pattern. We validated virtual 4D radiotherapy (v4DRT) along with exploring the acceptability of free-breathing volumetric modulated arc therapy (FB-VMAT). Methods and Materials: We assessed 10 patients with superficial EC through their real 4DCT (r4DCT) scans. v4DCT images were derived from the end-inhalation computed tomography (CT) image (reference CT) and the v4DRT dose was accumulated dose over all phases. r4DRT diaphragm shifts were applied with magnitudes derived from r4DCT scans; clinical target volume (CTV) dose of v4DRT was compared with that of r4DRT to validate v4DRT. CTV dosage modifications and planning organ at risk volume (PRV) margins of the spinal cord were examined with the diaphragm movement. The percentage dose differences (DDx) were determined between the v4DRT and the dose calculated on the reference CT image. Results: The CTV DDx between the r4DRT and v4DRT were within 1% in cases with RM <= 15 mm. The average Delta D-100% and Delta D-mean of the CTV ranging from 5 to 15 mm of diaphragm motion was 0.3% to 1.7% and 0.1% to 0.4%, respectively. All CTV index changes were within 3% and Delta D-1cc and Delta D-2cc of Cord PRV were within 1%. Conclusion: We postulate a novel method for evaluating the CTV robustness, comparable to the conventional r4DCT method under the diaphragm RM <= 15 mm permitting an impact of within 3% in FB-VMAT for EC on the CTV dose distribution. (c) 2023 Elsevier B.V. All rights reserved.