Planar and volumetric imaging dosimetry for longitudinal projection extended cone beam CT based adaptive radiotherapy

• Published in: Radiation measurements 2024-08, Vol.176, p.107179, Article 107179
• Main Authors: Rafic, K Mohamathu, Ebenezer, Suman Babu, Balasingh S, Timothy Peace, Sujith, J. Christopher, Abel, Juhan Thomas, Paul Ravindran, B.
• Format: Article
• Language: English
• ISSN: 1350-4487; 1879-0925
• DOI: 10.1016/j.radmeas.2024.107179

The objective of this study is to provide a detailed insight into the broad beam dosimetric characteristics of two commercial cone beam computed tomography (CBCT) imaging systems to complement the longitudinal projection extended CBCT based image guided adaptive radiotherapy (IGART). The absolute dose calibration, planar and volumetric dosimetric characteristics of two CBCT imaging systems viz., the Clinac 2100 C/D On-Board Imager (OBI) and the TrueBeam X-ray Imaging system (XI) (Varian Medical Systems, Palo Alto, CA) were investigated. Reference dosimetry specific to volumetric CBCT imaging mode was performed as per American Association of Physicists in Medicine (AAPM) task group (TG) 61 protocol using calibrated 0.6 cc Farmer ionization chamber (30010, PTW Dosimetry Company, Germany). The rotational planar and volumetric dosimetry was performed after calibrating the OCTAVIUS 1500 detector array as a mere photon detector, with and without the detachable hemisphere of 4D Modular phantom. The absolute dose of half-fan XI CBCT was found to be 1.2 times lower when compared to OBI CBCT. The abutting kV cone beam dosimetry specific to dual-scan CBCT fusion technique showed a wider in-plane profile for the OBI system when compared to the XI system, due to an additional field opening of 3.4 cm used for half-fan mode in the former. The reconstructed volumetric imaging dose distribution specific to half-fan geometry and dynamic movement of gantry, brought to light valuable details about the kV dose distribution. The planar and 3D imaging dosimetry reported in this study paves the way for the integration of volumetric imaging dose reconstruction capabilities during high precision radiotherapy to demonstrate a complete picture of the total dose delivered to the patient during the planned course of IGART. •Absolute dose calibration, planar and volumetric imaging dosimetry for two different kV CBCT systems (OBI and XI) were investigated.•A key factor in reducing imaging dose in the XI CBCT system is the incorporation of an additional titanium filter configuration while maintaining image quality.•In contrast to the PDD of narrow beam X-rays, the deep depth dose distribution exhibits broad beam characteristics of kV cone beams.•Dedicated 2D detector array with low dose sensitive detector elements enables dynamic/rotational dosimetry for accurate measurement of imaging dose.