Session Item

An adaptive technique combining intracavitary GYN applicators with interstitial needles is associated with improved outcomes in locally advanced cervical cancer involving tumor extensions to the parametrium. The multicenter EMBRACE II study protocol provides dose constraints as planning aims and dose limits for MR-delineated target structures. Expensive applicators needed to perform combined intracavitary/interstitial (IC/IS) brachytherapy and achieve the EMBRACE II planning aims are only available in a few specialized centers limiting the adoption of IC/IS brachytherapy. The purpose of this work is to show the feasibility of upgrading a widely used IC-only applicator; the CT/MR split-ring (E&Z BEBIG, Berlin, Germany) using relatively inexpensive 3D-printing technology to enable a more widespread and patient-specific use of IC/IS brachytherapy.  

The CT/MR split-ring applicator comes with disposable or reusable buildup caps that work as sleeves for each split-rings. A CAD model of the standard 5 mm buildup cap was designed using Fusion 360^TM (Autodesk Inc., California, USA). The cap was then extended outward and notches were modeled to allow attachment of guiding tubes used with the interstitial lunar ovoids of the Venezia IC/IS applicator (Elekta, Stockholm, Sweden). These upgraded sleeves were then printed using a Form3 SLA printer (Formlabs Inc., Massachusetts, USA) using two resins; Surgical Guide (ISO 10993 biocompatibility & 50 μm resolution) and BioMed Clear (USP Class VI biocompatibility & 100 μm resolution). Sleeves were steam sterilized at 132 °C in an autoclave for 4 minutes followed by a 25 minutes dry phase. Finally, the sleeves were tested for the following properties both pre- and post-sterilization: split-ring, guide-tube and fixation screw attachment.  

Figure 1. and 2. show the upgraded split-ring IC/IS applicator with the Surgical Guide and BioMed Clear sleeves respectively. Successful insertion of each split-rings and attachment of interstitial guide tubes was verified both pre- and post-sterilization. Guiding tube notches for interstitial needle obliquity angles of 15°, 30° and 45° were successfully tested. Fixation screw threads were found to be the most sensitive features of the printed sleeves. However, optimizing the protocol/models we increased the number of times the screw can be re-used before stripping the threads to over ten times which is satisfactory considering the disposable nature of these sleeves.  

3D-printing technology was successfully used to produce the affordable 3D-printed Montreal split-ring applicator for combined IC/IS brachytherapy. A collaboration is ongoing to develop a dedicated software module in Adaptiiv’s brachytherapy software (Adaptiiv Medical Technologies, Inc., Halifax, Canada) that would allow patient-specific needle trajectories (obliquity angles ≤ 45°) for adaptive brachytherapy.