Assessment of a source position checking tool for the quality assurance of transfer tubes used in HDR 192 Ir brachytherapy treatments.

PURPOSE: The determination of source positions before treatment is an essential part of the quality assurance (QA) associated with high dose rate brachytherapy treatments. The purpose of this study was to design and commission a tool to allow the quantification of source positions across multiple transfer tube types.

METHODS AND MATERIALS: A bespoke flexi-adapter jig, three transfer tube adapters, and a film piercing pointer were designed and built for source position QA across three transfer tube types-the standard, 6 French, and gynae transfer tubes. The jig was calibrated against a manufacturer source position check tool, and intratube and intertube source position variations investigated across a total of 40 transfer tubes, using strips of Gafchromic film irradiated at multiple positions 20 mm apart with a microSelectron V3 afterloader (Elekta, Holland). The performance of the jig in localizing the nominal dwell positions relative to the manufacturer check tool was assessed. Associated expanded uncertainties were quantified in line with the International Organization for Standardization Guidelines.

RESULTS: The mean expanded uncertainty associated with the use of the jig was 0.4 ± 0.0 mm (k = 1). The performance of the jig was 0.3 ± 0.0 mm, while the intratube and intertube source positional variations were observed to be within ±1.0 mm across most transfer tubes.

CONCLUSIONS: A bespoke flexi-adapter jig capable of allowing source position measurements to be carried out on various transfer tube types has been designed. Measurement results highlight the need for routine QA of all transfer tubes in clinical use.