An algorithm for computing customized 3D printed implants with curvature constrained channels for enhancing intracavitary brachytherapy radiation delivery

Brachytherapy is a widely-used treatment modality for cancer in many sites in the body. In brachytherapy, small radioactive sources are positioned proximal to cancerous tumors. An ongoing challenge is to accurately place sources on a set of dwell positions to sufficiently irradiate the tumors while limiting radiation damage to healthy organs and tissues. In current practice, standardized applicators with internal channels are inserted into body cavities to guide the sources. These standardized implants are one-size-fits-all and are prone to shifting inside the body, resulting in suboptimal dosages. We propose a new approach that builds on recent results in 3D printing and steerable needle motion planning to create customized implants containing customized curvature-constrained internal channels that fit securely, minimize air gaps, and precisely guide radioactive sources through printed channels. When compared with standardized implants, customized implants also have the potential to provide better coverage: more potential source dwell positions proximal to tumors. We present an algorithm for computing curvature-constrained channels based on rapidly-expanding randomized trees (RRT). We consider a prototypical case of OB/GYN cervical and vaginal cancer with three treatment options: standardized ring implant (current practice), customized implant with linear channels, and customized implant with curved channels. Results with a two-parameter coverage metric suggest that customized implants with curved channels can offer significant improvement over current practice.

I. Introduction

Automation science addresses the accuracy and quality of processes in a variety of applications from manufacturing to healthcare. Each year, over 500, 000 cancer patients worldwide are treated with brachytherapy [1], a form of radiotherapy where needles or implants are temporarily inserted into the body to guide small radioactive sources close to tumors (brachys: Greek for proximal). Brachytherapy is widely used to treat cancer in a number of anatomical sties: interstitial locations such as prostate, pelvic sidewall, breast, liver, brain; and intracavitary locations such as nasal cavity, throat, tongue, rectum, cervix, and the vaginal canal [2].