Interstitial cervical needle-guide ring-cap prototype for patient-specific ring-and-tandem brachytherapy.

Abstract

Purpose: We have developed a unique cap that could be paired with our existing commercially-available MRI-compatible ring-and-tandem applicator (R&T) that can provide a patient-specific cervical needle guide for hybrid intracavitary-interstitial brachytherapy (IC/ISBT).

Material and methods: Prototype guide caps with six channels for interstitial needles were rendered in SolidWorks (Dassault Systèmes SE, Vélizy-Villacoublay, France), coupled with Mick Radio-Nuclear Instruments (Mt Vernon, NY, USA) R&T. Prototypes were printed using Formlabs 3B printers and Gray Resin (Formlabs, Somerville, MA, USA). Achievable bend radii for interstitial needles were determined using custom jigs. A pilot cohort of previously-treated IC/ISBT patients was replanned with virtual needle paths reconstructed in EclipseBV (Varian Medical Systems, Palo Alto, CA, USA). Physical design constraints (bend radius, position) were used to determine the impact on EQD₂ for the HR-CTV D_90% and D_2cc for bladder, rectum, sigmoid, and small bowel.

Results: Software-rendered guide caps prototypes were 3D-printed and tested to all be physically compatible with our existing commercially-available R&T. The channels physically accommodated six interstitial needles with bending precision ±1°. Among the cohort, the HR-CTV D_90% was increased for every patient (9.60% max, 1.30% median) and D_2cc to the bladder, rectum, sigmoid, and small bowel was decreased (17.45% max).

Conclusions: We have designed and produced a guide cap prototype that can be used to improve our existing commercially-available R&T with IC/ISBT capabilities for customizable angles and positions. The guide caps have been shown to enhance dosimetry and can be used for patient-specific treatment.