Implementation and experimental evaluation of Mega-voltage fan-beam CT using a linear accelerator

Hao Gong, Shengzhen Tao, Justin D. Gagneur, Wei Liu, Jiajian Shen, Cynthia H. McCollough, Yanle Hu, Shuai Leng

Research output: Contribution to journalArticlepeer-review


Background: Mega-voltage fan-beam Computed Tomography (MV-FBCT) holds potential in accurate determination of relative electron density (RED) and proton stopping power ratio (SPR) but is not widely available. Objective: To demonstrate the feasibility of MV-FBCT using a medical linear accelerator (LINAC) with a 2.5 MV imaging beam, an electronic portal imaging device (EPID) and multileaf collimators (MLCs). Methods: MLCs were used to collimate MV beam along z direction to enable a 1 cm width fan-beam. Projection data were acquired within one gantry rotation and preprocessed with in-house developed artifact correction algorithms before the reconstruction. MV-FBCT data were acquired at two dose levels: 30 and 60 monitor units (MUs). A Catphan 604 phantom was used to evaluate basic image quality. A head-sized CIRS phantom with three configurations of tissue-mimicking inserts was scanned and MV-FBCT Hounsfield unit (HU) to RED calibration was established for each insert configuration using linear regression. The determination coefficient (R2) was used to gauge the accuracy of HU-RED calibration. Results were compared with baseline single-energy kilo-voltage treatment planning CT (TP-CT) HU-RED calibration which represented the current standard clinical practice. Results: The in-house artifact correction algorithms effectively suppressed ring artifact, cupping artifact, and CT number bias in MV-FBCT. Compared to TP-CT, MV-FBCT was able to improve the prediction accuracy of the HU-RED calibration curve for all three configurations of insert materials, with R2 > 0.9994 and R2 < 0.9990 for MV-FBCT and TP-CT HU-RED calibration curves of soft-tissue inserts, respectively. The measured mean CT numbers of blood-iodine mixture inserts in TP-CT drastically deviated from the fitted values but not in MV-FBCT. Reducing the radiation level from 60 to 30 MU did not decrease the prediction accuracy of the MV-FBCT HU-RED calibration curve. Conclusion: We demonstrated the feasibility of MV-FBCT and its potential in providing more accurate RED estimation.

Original languageEnglish (US)
Article number139
JournalRadiation Oncology
Issue number1
StatePublished - Dec 2021


  • Dose calculation
  • Electron density
  • Mega-voltage CT
  • Radiation therapy

ASJC Scopus subject areas

  • Oncology
  • Radiology Nuclear Medicine and imaging


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