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Updated: May 31, 2026
Irradiator Commissioning and Dosimetry for Assessment of LQ α and β Parameters, Radiation Dosing Schema, and in vivo Dose Deposition
Published on: March 11, 2021
Error identification in external beam radiotherapy using diode-based in vivo dosimetry during the transition from 2D
Ignatius Komakech1, Denis Okello2, Awusi Kavuma3
1Radiation Oncology Division, Uganda Cancer Institute, P.O. Box 3935, Kampala, Uganda; Department of Physics, Makerere University, P.O. Box 7062, Kampala, Uganda.
Background:
Radiotherapy aims to deliver a uniform dose within ± 5.0% of the prescription, while minimizing toxicity. Because treatment quality directly influences patient's treatment outcomes, error detection is critical for ensuring accuracy and safety. This study evaluated in-vivo dosimetry (IVD) as a quality assurance (QA) tool to detect treatment errors during the transition from two-dimensional radiotherapy (2DRT) with Cobalt-60 units to three-dimensional conformal radiotherapy (3DCRT) with linear accelerators.
Methods:
IVD was performed for 612 treatment fields across 493 patients treated with either 2DRT or 3DCRT. A calibrated entrance diode was placed on the patient's skin to measure delivered doses, which were compared with prescribed doses at relevant depths. Deviations exceeding ± 5% were investigated, with findings discussed with oncologists to enable immediate corrective action and subsequently communicated to staff to support continuous learning.
Results:
Ninety-two errors were identified. The most frequent causes were incorrect calculations (20.7%), procedural changes (15.2%), omission of tray/bolus in treatment time calculations (4.3%), and use of treatment times/monitor units without secondary physics verification (4.3%). Overall, 84.9% of the 612 measurements were within the ± 5% tolerance.
Conclusions:
IVD with a calibrated diode provides a simple and effective quality control measure for maintaining treatment accuracy. Systematic error analysis and structured staff feedback enhance awareness, strengthen safety culture, and improve patient care during technological transitions in radiotherapy.
