Author: Shashanksharad Kale, Gopishankar Natanasabapathi, Daya Nand Kishore Sharma 👨🔬
Affiliation: All India Institute of Medical Sciences (AIIMS), Department of Radiation Oncology, All India Institute of Medical Sciences 🌍
Purpose:
The study demonstrates a novel 3D printing method to fabricate an ion chamber insert (ICI) for absolute dosimetry purpose in gamma knife radiosurgery (GKRS).
Methods:
Our institute uses the gamma knife ICON model with 192 Cobalt-60 sources arranged in a hemispherical pattern, delivering radiation to the mechanical isocenter (UCP). For absolute dosimetry, a 16 cm Elekta solid water-based spherical phantom was positioned on the treatment couch with a frame adapter. A detachable commercial cylindrical ion chamber insert (CCI) holds pinpoint ion chamber within the spherical phantom to collect ionization charge from the radiation dose. A 0.016 cc ion chamber (PTW, Freiberg, Germany) was used to validate the point measurement results, following AAPM TG 178 protocol recommendations. The vendor used subtractive manufacturing (SM) to create a new CCI block, which was shipped abroad for design. A 3D printed chamber insert (3DPI) was made using SLA technology (Sonic Mighty 4K, Phrozen) with various resin materials to match the original CCI’s dimensions and accommodate 0.016 cc ion chamber volume. New 3DPI was placed in the phantom, and the dose rates of CCI and 3DPI were compared.
Results:
The 3DPI accurately mimicked the shape and dimensions of the CCI. The absolute dosimetry performed with 3DPI demonstrated a close agreement of 0.55 % with the CCI. The innovative 3DPI design created in this study used Vat photopolymerization printing technique with ultraviolet (UV) light to cure liquid resin into solid layers. The benefit of the printing technique is that it enables complex, water-equivalent geometries that mimic human tissue for accurate radiation dose simulations and modelling.
Conclusion:
The 3DPI proved to be a reliable, cost-effective and time saving alternative to the CCI for GKRS dosimetry. Future work aims to design a fully 3D printed spherical phantom as a commercial alternative for radiosurgery dosimetry.