Production of patient‐specific electron beam aperture cut‐outs using a low‐cost, multi‐purpose 3D printer

Electron beam collimators for non‐standard field sizes and shapes are typically fabricated using Styrofoam molds to cast the aperture cut‐out. These molds are often produced using a dedicated foam cutter, which may be expensive and only serves a single purpose. An increasing number of radiotherapy departments, however, has a 3D printer on‐site, to create a wide range of custom‐made treatment auxiliaries, such as bolus and dosimetry phantoms. The 3D printer can also be used to produce patient‐specific aperture cut‐outs, as elaborated in this note. Open‐source programming language was used to automatically generate the mold's shape in a generic digital file format readable by 3D printer software. The geometric mold model has the patient's identification number integrated and is to be mounted on a uniquely fitting, reusable positioning device, which can be 3D printed as well. This assembly likewise fits uniquely onto the applicator tray, ensuring correct and error‐free alignment of the mold during casting of the aperture. For dosimetric verification, two aperture cut‐outs were cast, one using a conventionally cut Styrofoam mold and one using a 3D printed mold. Using these cut‐outs, the clinical plan was delivered onto a phantom, for which the transversal dose distributions were measured at 2 cm depth using radiochromic film and compared using gamma‐index analysis. An agreement score of 99.9% between the measured 2D dose distributions was found in the (10%–80%) dose region, using 1% (local) dose‐difference and 1.0 mm distance‐to‐agreement acceptance criteria. The workflow using 3D printing has been clinically implemented and is in routine use at the author's institute for all patient‐specific electron beam aperture cut‐outs. It allows for a standardized, cost‐effective, and operator‐friendly workflow without the need for dedicated equipment. In addition, it offers possibilities to increase safety and quality of the process including patient identification and methods for accurate mold alignment.