Clinical applications with expired EBT-XD radiochromic film in radiotherapy

Radiochromic films are widely used in radiotherapy dosimetry for their high spatial resolution and near-water-equivalence. Nonetheless, these films are frequently purchased in bulk, leading clinical departments to accumulate stock beyond the manufacturer's expiration date. Assessing the dosimetric performance of expired films may confer economic and environmental advantages. This work evaluated whether expired EBT-XD radiochromic films remain suitable for specific radiotherapy dosimetry applications. Two expired batches were compared with a non-expired batch. Dose-response curves were generated using a 6 MV photon beam from a clinical linear accelerator. The films were tested for small-field output factor measurements and patient-specific quality assurance (PSQA) in volumetric-modulated arc therapy (VMAT) and stereotactic radiosurgery (SRS), employing gamma-index analysis. Results indicated that expired films exhibit reduced sensitivity relative to unexpired films, particularly at lower dose levels. However, acceptable dosimetric agreement with unexpired films was observed for small-field output factors and high-dose SRS PSQA cases, provided appropriate recalibration was applied. More pronounced discrepancies emerged in low-dose VMAT PSQA measurements, where diminished film sensitivity may have influenced the film's response. These findings suggest that expired EBT-XD radiochromic films may still provide useful dosimetric information as relative dosimeters for selected radiotherapy measurements, especially when measurements fall within the film's recommended dose range, and films are properly stored and recalibrated.