Multi-Material 3D Printing In Brachytherapy: Prototyping Teaching Tools

Abstract

The utilization of brachytherapy practice in clinics has been declining over the years. The decline has been linked to a variety of factors including a lack of training opportunities. To improve the quality of intracavitary and interstitial HDR brachytherapy education, a multi-material modular 3D printed pelvic phantom kit prototype simulating normal and cervix pathological conditions has been developed. This comprehensive training phantom is intended to serve as a novel aid in the “300 in 10 Strategy” put forward by the American Brachytherapy Society which calls to train 30 competent brachytherapists per year over the next 10 years.Patient anatomy was derived from anonymized pelvic CT and MRI scans from different representative patients who had been diagnosed with cervical cancer. The dimensions of patients’ uterine canal sizes and uterine body sizes were measured and used to construct a variety of uteri based off of the averages and standard deviations of the subjects in our study. The length of the uterine body was measured from top of the fundus to the top of the cervix. The width of the uterine body was measured at the top of the cervix and also measured across the midpoint between the cervix and the fundus. High risk clinical target volumes (HR-CTV) were also extracted from these patients. 3D Slicer (Slicer 4.10.1) was used to import and convert contoured DICOM data into a 3D model. Organs of interest for our prototype include the vaginal canal, uterus, and cervix. A standard rectum, and bladder were also printed. Individual STL files were imported into Autodesk Meshmixer (3.5.4) and manipulated to include more representative features such as hollowed out cavities and canals. Modular components of the phantom were designed and integrated into patient anatomy using 3D modeling software Shapr3D (Stratasys, 3.35.0). Flexible and rigid materials were assigned to each component of the phantom. Vero Clear (Stratasys) was assigned to rigid design components including modularity connections. Agilus30 (Stratasys) was assigned to the more flexible components including the vaginal canal, uterus, rectum, and bladder. Each flexible component was assigned a shore hardness value ranging from 30-80 to further individualize the level of flexibility. The finalized prototype was printed using a Stratasys J750 PolyJet printer. The prototype kit consists of four uteri. The three anteverted uteri in the kit are based on the smallest, the average, and the largest dimensions from our patient set. The fourth uterus is retroverted and uses average dimensions. The four uteri incorporate two embedded HR-CTVs through color staining in the uterine body prints. Four clip-on HR-CTV sections that expand outside the cervix and uterine body are also part of the kit to mimic different pathology. All uterus bodies and the vaginal canal are printed using clear Agilus (shore 30a), and the HR-CTVs are printed externally and into the uterine bodies using a blend of colored Vero and Agilus (shore 40a) as a means of evaluation for tandem/ovoids and needle placement. The bladder surface and rectum are printed in Agilus, shore 35a and 70a, respectively. The outer box was printed using Vero Clear, shore 90. The full kit which consists of an outer box, vulvar entrance, vaginal canal, four uteruses, two embedded HR-CTVs, four clip-on HR-CTVs, a standard bladder, and standard rectum, costs $631 in printing material expenses. This low-cost comprehensive training kit may be used to improve resident comfort in performing gynecological brachytherapy procedures.