Advancing dosimetry in cone-beam computed tomography: methodologies and key findings

Cone-beam computed tomography (CBCT) is widely used in radiology and radiotherapy, yet accurate dose assessment remains challenging due to wide X-ray beams, nonstandardized dosimetry protocols, and limited beam-collimation options. This study investigated a practical method for obtaining reference Computed Tomography Dose Index (CTDI) measurements on a CBCT system by introducing an external tungsten slit to generate a narrow beam compatible with the adopted dosimetry formalisms. Computed tomography air-kerma index measurements were performed using a 10-cm pencil ionization chamber, and dose-area product (DAP) values were obtained directly from the CBCT unit. The effective beam width was determined from projection images, and the system's geometric behaviour was characterized to support future modelling. A conversion factor between CTDI and DAP was derived for a head phantom, illustrating the feasibility and limitations of applying CTDI methodology to CBCT. The findings provide experimental data and geometric information that may support future Monte Carlo simulations and contribute to more standardized CBCT dose assessment.