Development of a dosimetric phantom using OSLDs or TLD-100 for external audits of high-dose-rate ¹⁹²Ir brachytherapy...

Calibration and quality control are fundamental to ensure that an accurate dose is delivered to a tumor, by HDR 192Ir radioactive sources in brachytherapy treatments. Consequently, it is essential for each radiation oncology center to implement a quality assurance program that includes an external audit. A cost-effective strategy, to meet the biannual requirements of licensing authorities, is the use of a well-established postal audit system employing phantoms and passive detectors.

The primary aim of this study was to design and construct a PMMA phantom measuring 14 × 14 × 14 cm³, featuring a rectangular insert with 1 slot on each side capable of accommodating either a single Al₂O₃:C OSLD or 4 LiF-100 TLD chips, along with a central channel for positioning the 192Ir source. The source is aligned perpendicular to the geometric center of the detectors to optimize dose measurements while minimizing geometric effects. Both the phantom and detector modalities were tested using a Nucletron HDR 192Ir source and its TPS. Correction factors were determined to increase measurement accuracy.

The developed system demonstrates sufficient accuracy to meet the ±5% acceptance criterion for remote audits of HDR 192Ir brachytherapy sources.

Following successful testing, it is now intended to cover the 106 brachytherapy centers in Brazil, with the potential for expansion to additional centers throughout Latin America. The feasibility of using both detector types has been positively confirmed, offering flexibility and robustness to the audit system.