A review of 3D printing utilisation in radiotherapy in the United Kingdom and Republic of Ireland

Comparative study of flexible 3D printing materials for clinical application as boluses in radiotherapy

PURPOSE

3D-printing is increasingly used in radiotherapy for precise bolus fabrication. While materials like ABS and PLA are common, flexible 3D-printing materials may better adapt to anatomical variations. However, a comprehensive evaluation of these flexible materials remains limited.

METHODS

A breast silicone phantom (Phantom) was designed based on a small-breast model and printed. To simulate treatment-related swelling, a second phantom with a 3 mm expansion (PhantomExp) was also created. A virtual bolus (0.5 mm thick) was designed and 3D-printed using twelve materials, including direct printing (ABS, PLA, TPU, MED610, Biomed Flex 80, Biomed Elastic 50, Elastic 50, Flexible 80, ElasticClear, AmSil silicone) and casting (Dragon-Skin 30 and Silbione silicones). Three tests were conducted: 1. Bolus Characterization: Printing cost and time, CT image analysis, and print fidelity were evaluated. 2. Adaptability Test: Air volume between the bolus and Phantom was measured using CT images, and compared to the air volume between the bolus and PhantomExp to assess adaptability. 3. Dosimetric Test: Film dosimetry was used to compare the planned and measured surface doses on the Phantom with each bolus.

RESULTS

Most of the materials achieve high printing accuracy (<0.3 mm). Air volume was greater with PhantomExp due to expansion, but silicone materials and BiomedElastic50 adapted well to the shape changes. Dosimetric differences were under 3 %, confirming that the bolus effect was achieved.

CONCLUSIONS

Silicone-based options produced through casting are the most favourable when time constraints are not critical.

IPEM topical report: guidance on 3D printing in radiotherapy

There has been an increase in the availability and utilization of commercially available 3D printers in radiotherapy, with applications in phantoms, brachytherapy applicators, bolus, compensators, and immobilization devices. Additive manufacturing in the form of 3D printing has the advantage of rapid production of personalized patient specific prints or customized phantoms within a short timeframe. One of the barriers to uptake has been the lack of guidance. The aim of this topical review is to present the radiotherapy applications and provide guidance on important areas for establishing a 3D printing service in a radiotherapy department including procurement, commissioning, material selection, establishment of relevant quality assurance, multidisciplinary team creation and training.

Characterization and evaluation methods of fused deposition modeling and stereolithography additive manufacturing for clinical linear accelerator photon and electron radiotherapy applications

PURPOSE

To propose comprehensive characterization methods of additive manufacturing (AM) materials for MV photon and MeV electron radiotherapy.

METHODOLOGY

This study investigated 15 AM materials using CT machines. Geometrical accuracy, tissue-equivalence, uniformity, and fabrication parameters were considered. Selected soft tissue equivalent filaments were used to fabricate slab phantoms and compared with water equivalent RW3 phantom by delivering planar 6 & 10 MV photons and 6, 9, 12, 15, & 18 MeV electrons. Finally, a 3D printed CT-Electron Density characterization phantom was fabricated.

RESULTS

Materials used to print test objects can simulate tissues from adipose (relative electron density, ρe=0.72) up to near inner bone-equivalent (ρe=1.08). Lower densities such as breast and lung can be simulated using infills from 90 % down to 30 %, respectively. The gyroid infill pattern shows the lowest CT number variation and is recommended for low infill percentage printing. CT number uniformity can be observed from 40 % up to 100 % infill, while printing orientation does not significantly affect the CT number. The measured doses using the 3D printed phantoms show to have good agreement with TPS calculated dose for photon (< 1 % difference) and electron (< 5 % difference). Varying the printed slab thicknesses shows very similar response (< 3 % difference) compared with RW3 slabs except for 6 MeV electrons. Lastly, the fabricated CT-ED phantom generally matches the lung- up to the soft tissue- equivalence.

CONCLUSION

The proposed methods give the outline for characterization of AM materials as tissue-equivalent substitute. Printing parameters affect the radiological quality of 3D-printed object.