Abstract
BACKGROUND: Pre-irradiation of ionization chambers is widely recommended to stabilize output readings for reference dosimetry in radiation therapy. However, the specific pre-irradiation requirements for different chamber models, particularly under strictly controlled conditions that isolate chamber performance, remain unclear. PURPOSE: This study aimed to quantitatively evaluate the pre-irradiation dose required to stabilize the output of various reference-class ionization chambers, while minimizing the influence of environmental and system-level uncertainties. METHODS: Twelve reference-class ionization chambers (Exradin A12, A1SL; IBA CC13, FC65G; PTW 30013, 31021) were evaluated under strictly controlled conditions (room temperature: 25 ± 1°C, water temperature: 25.00 ± 0.01°C, relative humidity: approximately 50%). Output stability was assessed using a 10 MV photon beam from a TrueBeam linac. Chamber readings were measured using an RT521R2 electrometer and normalized to an adjacent external monitor chamber. Readings are defined as stable if the reading variation is <0.1% and does not exhibit any trending. The optimal number of pre-irradiation exposures and corresponding doses were determined for each chamber. RESULTS: For the large-volume chambers (Exradin A12, IBA FC65G, PTW 30013), output variation was within ±0.05% from the first irradiation, suggesting that pre-irradiation may be unnecessary. In contrast, the middle-volume class ionization chambers (Exradin A1SL, IBA CC13, PTW 31021) exhibited variations of up to ±0.25%, and required up to 100 MU × 25 (approximately 21.25 Gy) of pre-irradiation to achieve stability under the controlled experimental conditions of this study. CONCLUSIONS: This study demonstrated that the required pre-irradiation dose varies depending on the type of ionization chamber, and that the output variation is significantly lower than the previously reported 1%. These results may help streamline clinical reference dosimetry by tailoring procedures to each chamber.