Development of a brachytherapy device for cervical cancer

Abstract

Brachytherapy is recommended in the treatment of cervical cancer. In case of a tumour extending lateral to the pelvic wall or more than 0.5 cm from the vaginal surface, current applicators are not sufficient to irradiate the target area. Therefore, the use of extra free-hand needles is required. Free-hand placement of interstitial needles is operator/experience dependent. The goal of this study is to develop a device that is able to irradiate the tumour in case of lower vaginal involvement or distal parametrial extension.

Based on the design criteria, a new concept has been developed. The concept is a personalised 3D-printed vaginal template with curved channels based on the MRI scan from the patient. Channel curvature constraints were examined by conducting an experiment with a separate 3D-printed template. The effects of two different needle tips (round and sharp) and 12 different curvatures (radius = 20 - 75 mm, with increments of 5 mm) on the required insertion force have been examined. A 3D-printed template with different curvatures has been suspended in a 10 m\% gelatin phantom. Needles were inserted with an obturator at a speed of 5 mm/s, using a linear stage. Axial forces were measured. The data was processed and compared with a subjective user experiment of manual insertions. To examine technical feasibility of the concept, two relevant cases of cancer were used to create personalised applicators. The accuracy of the needle tip placement with these templates has been tested.

No differences have been found in maximum required insertion force for a round and sharp needle tip while passing through a template with different curvatures and while puncturing tissue. For the different curvatures, significant differences in axial force have been found for curvatures with radii $\leq$ 50 mm. Buckling behaviour occurred for radii $\leq$ 35 mm. The user experiment indicates a threshold value of 35 mm for the minimum radius for a round and sharp needle that is still comfortable to insert. Two relevant cases of vaginal cancer were successfully translated into personalised applicators. The mean accuracy of the needle tip placement was 3.9 mm. All values were < 8 mm. The curvature constraints have been used to verify that the target area can be reached.

A personalised 3D-printed template with curvature constraints has been proposed as an improved method for the practice of brachytherapy in case of cervical cancer with distal parametrial extension or lower vaginal involvement. Further development and research are required to optimise the concept and verify clinical feasibility.