GSOR9 Presentation Time: 9:40 AM: 3D-Printed Ovoids with Rotational Needle Guides for Patient-Specific Hybrid Applicator Gynecologic Brachytherapy

Abstract

<h3>Purpose</h3> To develop ovoid caps having a rotational guide to assist in needle insertion to predetermined locations for preferential dose deposition. <h3>Method</h3> The custom ovoids were designed to be compatible with a titanium FSD tandem and ovoid applicator set and plastic needles (Varian, Palo Alto, CA). The rotational needle guides are designed in three parts as illustrated in Figure 1. For each ovoid, there are three needle guides on both sides of the colpostat tandems: anterior, middle, and posterior pairs. The anterior and middle needle guides are designed perpendicular to the colpostat tandem while the posterior needle guides are angled 30-degrees posteriorly. The opening for the colpostat tandem is contained within the anterior section. The posterior section of the ovoid is attached to the anterior section with a titanium screw. The middle ring is free to rotate at predetermined angles in a plane perpendicular to the tandem direction. Titanium set screws fix each component to the colpostat tandems. The custom ovoid design is fabricated with a FormLabs Form 3B 3D printer (FormLabs, Somerville, MA) using a USP (U.S. Pharmacopeia) Class VI biocompatible certified Bio-Clear resin. Printed ovoid caps are sterilized for use using a 121-degree Celsius Gravity cycle for 30 minutes. The original stainless-steel mandrins used to stiffen the needles during implantation were replaced with 16 gauges wire to provide sufficient insertion support while providing more flexibility in negotiating the needle guide angles. <h3>Result</h3> The 3D-printed ovoids were used for a patient presenting with stage IIB cervical cancer receiving 2750 cGy in five fractions of brachytherapy. Two needles were placed within the medial posterior and medial middle guides of the patient right ovoid. The middle guide was rotated 10 degrees towards the patient right (Figure 2B). The acrylic-based 3D-printed resin material has HU values closer to surrounding tissues compared to the high-density polyethylene ovoids of the standard T&O set. <h3>Discussion</h3> Hybrid gynecologic applicators are beneficial in achieving dose distributions beyond the traditional "pear-shape" but can still be limited by the applicator design. Rotational needle guides within the ovoids provides added freedom in designing a patient-specific implant to reduce dose to adjacent organs at risk.