The ability to independently verify the source strength of a brachytherapy source in a radiotherapy department is necessary to ensure accurate patient treatment delivery. This is most commonly completed with a well chamber designed for the calibration of brachytherapy sources; however, these chambers do require maintenance and calibration periodically. By developing an easily reproduced 3D printed jig compatible with a calibrated cylindrical chamber, this provides a reliable option for independent source strength verification.
Tinkercad was used to create a simple jig with a minimalistic design to reduce scatter. Using a Raise 3D Pro 2 dual extrusion printer and 1.75mm PLA filament, the jig was manufactured in house as a secondary calibration solution for brachytherapy sources. Features of the jig design included 10% infill with grid pattern for lightweight but structurally sound design, multiple measurement distances for 7 distance method and calibration, ability for interchangeable plastic needles and cylindrical chambers and optimisation of ‘fit’ between pieces to ensure integrity and easy construction. A full uncertainty budget was also developed as part of the jig design to account for additional errors when measuring in air rather than in a well chamber.
The jig was designed, printed and successfully used to verify source strength of Varian Ir-192 brachytherapy source. The certificate of the Ir-192 source had an Reference Air Kerma Rate (RAKR) of 50.10 mGy/h at 1m ± 5 %. The well chamber measured this at 49.64 mGy/h ± 1 % and the jig at 50.47 mGy/h ± 2.4 %. The largest source of uncertainty in the in-air calibration came form the interpolation between Nk values for Ir-192.
A reproducible, robust and lightweight in air calibration jig was designed for quality assurance of brachytherapy sources. The jig was successfully used to calibrate an Ir-192 brachytherapy source with RAKR measurements comparable to that of a well chamber. The low cost option allows a secondary source check for brachytherapy sources, this is particularly useful when well chambers are requiring calibration or repair.
Ms Emily Simpson-Page –Emily is a Radiation Oncology Medical Physics Registrar at the Royal Brisbane & Women's Hospital in Queensland.
A/Prof Tanya Kairn –Tanya Kairn is the principal medical physicist and RSO at the Royal Brisbane & Women's Hospital and is an adjunct associate professor at the University of Queensland.