Feasibility of Megavoltage CT for High-Dose Retrospective Planning of Helical Tomotherapy and Linac Treatment Plans: Hepatocellular Carcinoma Cancer Case

Introduction: This work aimed to investigate the use of megavoltage CT (MVCT) images for retrospective planning in high-dose and low-fractionation radiation techniques for Helical Tomotherapy and Linac. Material and Methods: This work used pre-treatment MVCT images for retrospective planning in high-dose hypofractionation of eight hepatocellular carcinoma (HCC) patients using the stereotactic body radiation therapy (SBRT) technique. The dose per fraction was 5.5–8 Gy in 4–5 fractions. As the patients were scanned with Helical Tomotherapy (HT) MVCT before each treatment, the selected MVCT images were registered to kVCT for re-contouring, and then the images were exported to HT and Linac for planning. The kVCT scan images were also exported from HT to Linac for planning in Linac. The final plans were compared and analyzed using the following parameters: conformity index (CI), paddick conformity index (PCI), homogeneity index (HI), and organs at risk (OAR) constraints. The dose verification was performed by gamma passing rate (GPR) test using EBT3 films. Results: CI values were found in the range 0.7–1.00 (CI̅: 0.95 ± 0.063), PCI values were found from 0.81 to 0.96 (PCI̅: 0.87 ± 0.04), and HI values were found from 0.02 to 0.53 (HI̅: 0.16 ± 0.12). OAR constraints were clinically acceptable. Distance-to-agreement of 3mm and dose difference of 3% was used as GPR criteria for each plan modality. Conclusion: These results suggest that MVCT could be used as an alternative modality for high-dose re-planning in HT and Linac as well as being used for position verification.