3D printed intracavitary brachytherapy moulds: A new workflow for improved efficiencies

Background and Purpose:
Intracavitary vaginal vault brachytherapy is standard of care for the treatment of gynaecological carcinoma thinner than 5 mm, utilising single- and multi-channel cylinders where uniform and/or asymmetric dose distributions are required. Personalised moulds are necessary to prevent underdosing of clinical target volume if poor contact between a proprietary cylinder and mucosa is evident [1]. Fabrication based on vault impression is however resource-intensive and susceptible to inaccurate catheter placement. 3D printing has potential to mitigate these issues [2]; our aim is to determine potential workflow efficiency improvement.

Methods:
A parallel workflow for fabrication of 3D printed vaginal moulds was introduced for a patient diagnosed with T4N1M0 grade 3 Endometrial Adenocarcinoma who exhibited large (> 5 mm) airgaps between cylinder and vaginal mucosa in CT-simulation. This involved contouring the standard custom mould within the Oncentra brachy TPS v4.1.6 (Elekta AB, Stockholm, Sweden). A 3D printed custom mould was created in flexible TPU filament from the DICOM RS file, which included delineated Proguide sharp 6F catheter channels (Fig. 1a). Print fidelity together with catheter fit was assessed against the standard mould used on patient treatment.

Results:
Fabrication of a patient-specific 3D printed vault mould was achieved with sub-mm accuracy compared to the standard used on treatment (Fig. 1b). Meanwhile, Proguide catheters were observed to fit snugly into the printed source channels without obstruction.

Fig. 1: (a) Virtual 3D model of vaginal mould applicator (b) Corresponding 3D printed mould with backlighting to show catheter channels (red) and homogeneity.

Conclusions: 3D printing of vaginal mould applicators was realised as proof-of-concept. By outsourcing the fabrication process, the otherwise resource intensive mould-room process was entirely removed. For future work, we propose imaging of the patient with suitable gel material in-situ intravaginally to allow direct creation of the DICOM RS file with optimised catheter positions, removing the need for an impression altogether.

References:
[1] E Khoury, I Dumas and A Tailleur et al (2015). “Adjuvant brachytherapy for endometrial cancer: Advantages of the vaginal mold technique” Brachytherapy 14(1):51–55
[2] R Laan, R Nout and J Dankelman et al (2019). “MRI-driven design of customised 3D printed gynaecological brachytherapy applicators with curved needle channels” 3D Printing in Medicine 5:8

Judith Martland

Northern Sydney Cancer Centre, RNSH
Medical Physicist

Judith is a Senior medical physicist at the Northern Sydney Cancer Centre whose responsibilities include lead physics support of the clinical brachytherapy service