Purpose: To develop a custom 3D printed HDR plesiotherapy applicator for localized squamous cell carcinoma on the glans penis.
Methods: A rigid shell-like applicator having eight channels for standard plastic catheter insertion was designed such that it could slide onto the penis. A spiral pattern was designed at the distal end to accommodate the spherical curvature of the glans while achieving a large radius of curvature for smooth source wire transfer. This applicator was printed on a SLA 3D printer to achieve a highly smoothed finish for standard plastic catheter insertion. Before putting on the applicator, a custom-made silicone bolus/sleeve (4mm-thickness) was placed to provide space from the source to reduce the surface dose and for patient comfort. Tests were conducted to ensure the standard plastic channel diameter and radius of curvature were appropriate for guide tube insertion and source delivery.
Results: With the bolus and applicator placed, a patient with a rcT1a penile cancer was imaged on a CT scanner with wires placed in the channels for treatment planning digitization. For a penis of diameter ~30mm, a 36mm applicator with a 26mm silicone bolus provided sufficient immobilization with minimal air gaps. Brachytherapy planning was performed with a prescription dose of 40 Gy in 10 fractions at the surface, and 35 Gy at 5mm depth, bidaily. Dose coverage to the targeted glans was 94%(D90). During the course of treatment, a highly reliable and reproducible setup (5-10 minutes setup time) was made possible. 6-month follow-up monitoring showed no significant changes in urinary and sexual function.
Conclusion: A 3D printed patient specific applicator with a silicone bolus was shown effective in providing a reproducible setup and dose delivery for HDR brachytherapy plesiotherapy.