Abstract: Background and purpose: The precise radiotherapy of tumor site depends on the precise dose distribution of the therapeutic target. The purpose of this study was to explore the influence of different computed tomography value to the relative electron density (CT-RED) calibration curve on the dose distribution of tumor and the method of fitting one CT-RED curve. Methods: Two CT scanners in Fudan University Shanghai Cancer Center were used to scan the CIRS-062 electronic density phantom, the CT- RED calibration curves of different sites (head, chest and abdomen) were obtained, and an improved CT-RED curve was optimized based on each curve. The original and modified CT-RED curves were used to calculate the dose distribution of planning target volume (PTV) (nasopharyngeal cancer, lung cancer and cervical cancer, 16 cases of each) and organ at risk (OAR) in the treatment planning system (TPS). Finally, 5 cases of each tumor were selected to verify the feasibility of optimized CT-RED. Results: The dose calculated by different CT-RED curves showed minimal differences in cervical cancer and head and neck tumor ( ＜ 1.00% and  ＜ 1.13%), but there was a large difference (2.50%) in low-density area of lung tumor. There was no significant difference ( ＜ 1.00%) between the optimized CT-RED curve and the original six CT-RED curves in the PTV and OAR. Conclusion: The corresponding CT- RED calibration curve should be selected to calculate the dose distribution of different tumors. And the improved CT-RED calibration curve scheme can also be used to reduce the potential risk of wrong calibration curve selection in the center with multiple positioning CT.

Key words: Relative electron density, Different computed tomography value to the relative electron density, Radiotherapy