MSS02 Presentation Time: 3:50 PM: Feasibility of 3D-Printed Endorectal High Dose Rate Brachytherapy Applicator: A Single Patient Case Report

Abstract

<h3>Purpose</h3> Endorectal brachytherapy is an effective treatment for select patients with rectal cancer, particularly in re-irradiation cases. In the United States, this technique is underutilized. Herein we describe, to our knowledge, the first report of a previously irradiated rectal cancer patient treated with a 3D-printed Endorectal High Dose Rate Brachytherapy Applicator. <h3>Materials and Methods</h3> A 64 year old morbidly obese female who was previously irradiated for endometrial cancer in 2009 presented with newly diagnosed uT3N0, MRI T2N0 rectal adenocarcinoma. Previous radiation records were no longer available other than a treatment summary identifying a total dose of 50.4 Gy in 28 fractions was delivered to the pelvis. Total neoadjuvant therapy was recommended with a watch and wait approach given surgical difficulties in a morbidly obese woman previously irradiated. The mass began 3 cm from the anal verge, extended nearly 5 cm superiorly, and circumferentially involved less than 50% of the rectal lumen. Fiducial markers were placed in the 4 cardinal directions. A 2.5 cm diameter, 18 cm length, 13 multichannel applicator (1 central channel, and 12 outer channels 5mm from cylinder surface) design was designed in <i>Autodesk Fusion 360</i> to ensure adequate coverage (see figure 1). 3D printing was achieved with a FormLabs 3 printer using Surgical Guide V1 resin. [JF1] The applicator was placed on the first day of treatment at CT simulation. The patient was placed in the prone position with the applicator inserted in the rectum. Treatment was delivered in 4 consecutive daily fractions of 6.5 Gy for a total of 26 Gy. <h3>Results</h3> The CTV volume was 19.8 cc and maximum tumor depth was 13 mm. Tumor coverage was excellent with a V200 of 6%, V150 of 23%, V100 of 70%, D90 of 83%. Target coverage was sacrificed to reduce the V200, given unknown previous radiation fields. The bladder D2cc dose was 5.4 Gy[JD2] [MS3] . The patient had complete resolution of rectal bleeding by the 4^th fraction. She reported no acute toxicities. At the time of this report, the patient is 1 month post brachytherapy with no reported toxicities with significantly easier bowel movements and continues to have no bleeding. <h3>Conclusion</h3> To our knowledge, this is the first reported 3D printed Endorectal High Dose Rate Brachytherapy Applicator used in clinical practice. In this case, the patient had early response with no adverse events. We believe 3D printing is a useful tool for Brachytherapists, and a feasible treatment option for rectal cancer patients.