This feasibility study aims to determine if a low-cost 3D printer (BitsFromBytes 3D Touch) with ABS plastic can print custom mould structures and catheter channels defined in a brachytherapy treatment planning system (Nucletron Oncentra) for patient-specific treatment. Printer accuracy was evaluated through physical measurement, and print quality was investigated by adjusting print parameters (print speed, layer thickness, percentage infill). Catheter positioning and reproducibility were measured over repeated insertions. ABS plastic water equivalency was investigated by comparing Ir-192 HDR source dose distributions, measured with radiochromic film, in ABS plastic and in water. Structures and catheter channels were printed accurately to within 0.5 mm laterally and 1 mm in the vertical print direction. Adjusting print parameters could reduce print time, albeit with reduced print quality. 3.5 mm channel diameters allowed for easy catheter insertion. Catheter positioning was reproducible to within 0.5 mm but, because of catheter flex within the channel, was on average 1 mm offset from defined TPS positions. This offset could be accounted for by repeating the treatment planning CT scan with the printed mould positioned on the patient. Dose attenuation in ABS plastic and in water was equivalent to within the measurement limitations. While clinical uses for this particular low-cost printer and ABS plastic are limited by print size restrictions and non-certification for biocompatibility, it has been demonstrated that a low-cost 3D printer set-up can accurately create custom moulds and catheter channels potentially acceptable for clinical use.
This study confirms that the regionally relevant practice of CT-based 3D-optimised planning results in improved tumour dose coverage compared with traditional points-based planning methods and also improves dose to the rectum and bladder.
The use of a non-water-equivalent personalised mould for gynaecological brachytherapy treatments can result in a substantial dose reduction at the treatment site, compared to calculated dose, in lieu of a dose calculation algorithm capable of modelling non-water-equivalent materials. This study describes the characterisation of the radiological properties of a brachytherapy applicator moulding material. Simple line source correction factors for an Ir source are obtained through Monte Carlo simulations and verified by film measurements. The dwell position corrections are used to estimate aggregate correction factors for dose deliveries that involve multiple dwell positions, in terms of treatment length, applicator radii and depth of reference dose. For the Fricotan moulding material used locally, the dose reductions varied from 1% for an applicator radius of 0.5 cm to> 4% for radii exceeding 2 cm. The method described in this paper could be used to develop correction factors for other non-water-equivalent moulding materials, in a TG-43UI dose calculation environment.
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