Error identification in external beam radiotherapy using diode-based in vivo dosimetry during the transition from 2D to 3DCRT in Uganda.

Abstract

BackgroundRadiotherapy 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.MethodsIVD 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.ResultsNinety-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.ConclusionsIVD 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.