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

Abstract

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 ($${R}^{2}$$ R 2 ) 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 $${R}^{2}$$ R 2 > 0.9994 and $${R}^{2}$$ R 2 < 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.

Linear Accelerators in Teleradiotherapy

“…Linear accelerators consist of multiple separate technological components that function as a single unit to accelerate electrons to high energies with high-frequency waves, striking a target and producing a photon beam, which is then aligned, shaped, and measured prior to clinical use (15). The main components of a linear accelerator are: accelerator tube, electron gun, accelerator waveguide, high-frequency wave source (klystron or magnetron), electron beam rotation magnet, accelerator head, therapy table, control panel, monitoring system (16) (Figure 1).…”

Can a ToF-PET photon attenuation reconstruction test stopping-power estimations in proton therapy? A phantom study

“…It has been pointed out in the past that the degeneracy of Hounsfield values and proton stopping-power can also be avoided if the CT imaging is performed with photon energies in the MeV range (MVCT) (Langen et al 2005, Newhauser et al 2008, Moyers et al 2010, Marzi et al 2013, Gong et al 2021. The Compton effect, which dominates in this energy regime, provides a simple linear relationship between μ and n e .…”