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Technological developments in 3D printing resulted in applications in several fields including radiotherapy. It brings the opportunity to research and clinical departments to develop new technologies and prototypes reaching the same level of accuracy as commercial vendors. This report describes some of the applications of 3D printing in our clinic and focuses on the 3D printing technology rather than the detailed description of each application. 

Commercial and in-house developed 3D printers were introduced in our research department early in 2018 aiming to manufacture and test an in-house developed brachytherapy applicator for rectal cancer and develop a new device for applicator commissioning. This technology was then employed to develop custom 3D printed homogeneous and heterogeneous phantoms based on patient anatomy for dosimetry and imaging and also to develop prototypes of motion platforms currently being used in combination with 3D printed phantoms for dosimetry. Although great geometrical accuracy can be obtained, the material properties are often not well known. In this study, more than 20 types of commercial materials (e.g., PC, PLA, ABS, PP, Nylon, and TPU) were tested. In addition, a custom filament including ≈17% of Ca was developed to mimic bone.

Fast prototyping using 3D printing technologies was essential to quickly design and manufacture applicators, phantoms and other devices with limited costs. The brachytherapy applicator (Figure 1a) was eventually patented and further developed into a commercial product by a major radiotherapy device vendor whilst the applicator commissioning device (Figure 1b) is currently under clinical implementation. Treatment verification methods are currently being developed using prostate (Figure 1c) and head phantoms (Figure 1d) to perform static and dynamic measurements using the 3D printed motion platform (Figure 1d). A phantom (Figure 1e) based on the anatomy of a large patient (developed due to the lack of commercial alternatives) was used to evaluate extended field-of-view CT reconstruction. Tissue-equivalent materials for photon and proton therapy are desirable for imaging and dosimetry with bone equivalent materials being the main challenge. Our custom bone material (Figure 2a) showed similar behaviour as commercial tissue-mimicking inserts regarding density, Hounsfield Units, and stopping power ratios. In addition, mass attenuation coefficients are similar to ones obtained using bone composition described in the literature. 

3D printing applications in radiotherapy or by specialized companies will continue to increase providing an essential tool for affordable innovation and customization (e.g. patient or application-specific phantoms). Nonetheless, in-house developed prototypes need medical certification through regulations, risk analysis, documentation and other requirements for implementation for which hospitals may not be prepared.