TITLE:
Quantification of Imaging Doses from Cone Beam Computed Tomography System at Steve Biko Academic Hospital
AUTHORS:
Precious Mathebula, Lutendo Christopher Nethwadzi, Sonwabile Ngcezu
KEYWORDS:
Imaging Doses, Radiation Exposure, Stochastic Effects
JOURNAL NAME:
Open Access Library Journal,
Vol.13 No.7,
July
8,
2026
ABSTRACT: Introduction: In radiotherapy, to effectively treat tumours, a high level of precision, accuracy, and reproducibility is necessary. This guarantees that a sufficiently high dose reaches the tumour while preventing radiation exposure of the surrounding healthy tissues. Cone Beam Computed Tomography (CBCT) is an image guidance technique used by the Steve Biko Academic Hospital (SBAH) radiation therapy department to ensure accurate patient setup and position verification before treatment delivery. CBCT patient verification offers valuable insights into internal anatomical structures but involves the use of ionizing radiation. Consequently, the verification process using CBCT may deliver significant additional radiation doses beyond the prescribed treatment dose due to its frequent use. In radiotherapy, during position verification before treatment, it is vital to employ an imaging modality that allows visualization of both soft tissue and bony anatomy to ensure accurate patient positioning while keeping the dose as low as reasonably possible. To this end, this study seeks to quantify doses associated with setup positioning verification without compromising image quality and to develop recommendations to avoid stochastic effects arising from unnecessary doses. This was achieved by computed tomography dose index (CTDI) measurements, from which the dose-length product (DLP) was calculated, which was then converted to the effective dose. Materials and Methods: The study was conducted at SBAH in the radiation oncology department. The University of Pretoria Research Ethics Committee approved this research (Ethics Reference No.: 2220/2022). To ensure that the CBCT system met the required image quality, the Catphan model 503 (Salem, NY, USA) imaging phantom was used. CTDI measurements were performed using head and body phantoms, an ionization chamber, and an electrometer. The CTDI dose was measured for different cancer treatment setup verification imaging protocols, including head-and-neck, pelvis, and prostate protocols. Measurements were conducted for 100 and 120 kV. The CTDI dose was measured based on different parameter settings in the setup imaging protocols, including frame, field of view, collimator, and filter. The measured CTDI and calculated DLP were used to quantify imaging doses. The DLP values were converted to effective doses using factors from the American Association of Physicists in Medicine (AAPM) report 96. Results: The image quality test findings matched the South African Standards for Quality Assurance in Radiotherapy (SASQART) and the manufacturer’s tolerances. In adults, the CTDI dose for head and neck ranges from 0.23 to 0.52 mGy, for the pelvis from 3.1 to 6.44 mGy, and for the prostate from 3.9 to 13.46 mGy per imaging protocol. For paediatric protocols, the CTDI dose ranges from 0.19 to 0.40 mGy for head and neck, 6.00 to 12.10 mGy for pelvis, and 6.00 to 24.00 mGy for the abdomen per imaging protocol. Conclusion: This study has revealed that the doses of CBCT radiation used during verification procedures are generally low in areas such as the head and neck. However, for pelvic sites such as the prostate, where detailed visualization of soft tissue is necessary, the doses tend to be relatively high. The results showed that, per fraction, a maximum CTDIvol of approximately 24 mGy can be delivered to paediatric patients. This is noteworthy because repeated imaging during treatment may pose significant risks related to the stochastic effects of radiation.