ESTRO 2024 - Abstract Book

S2088

Clinical - Sarcoma, skin cancer, melanoma

ESTRO 2024

Conclusion:

Radiotherapy might be an effective method of symptom palliation in osteosarcoma patients but the survival rate remains poor. There is a significant need for further investigation in the metastatic osteosarcoma.

Keywords: osteosarcoma, palliative radiation therapy,

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Digital Poster

Custom Skin Collimation for Electron Treatments from 3D-Printed Dissolvable-Moulds

Alek K Rapchak, Sean A Roles, Daniel G McDonald, Matthew R Maynard, Jean L Peng

Medical University of South Carolina, Radiation Oncology, Charleston, SC, USA

Purpose/Objective:

Sparing normal tissue during radiotherapy skin treatments using megavolt energy electrons sometimes requires the use of skin collimation placed on the patient in addition to secondary beam collimation. For many years, thin lead sheets were placed around the site to attenuate electrons where normal tissue needed to be spared but electron cutouts could not block the primary beam. Patient moulds could be produced and lead hammered to more conform to the patient, but the opening may not account for the planned treatment area and the time it takes to produce can be taxing on the staff. We have developed a skin collimation method using Cerrobend poured in a 3D printed mould--designed from the planning CT--that can be dissolved in water.

Material/Methods:

Polyvinyl alcohol (PVA) is a readily available 3D printing material. It is mostly used in multi-nozzle FDM 3D printers as a support material due to its being dissolvable in room temperature water. Instead of support, we have used PVA as the sole material in creating these moulds. The melting point of Cerrobend (70°) is much lower than the PVA (200°) and can be poured directly into the mould as a liquid. Once the Cerrobend has been solidified, the entire mould can be submerged in room-temperature water until the PVA is completely dissolved. The remaining Cerrobend shield is then covered with tape or wax to prevent skin contact and attenuate bremsstrahlung radiation. The shielding is designed using the free software, 3D Slicer, with the needed Radiotherapy extensions to use DicomRT files. Using images from the CT sim in addition to the plan and contours from the treatment planning system, we design the shielding by creating a contour extending from the surface with an opening where the wire is marked. The thickness (mm) of the shielding is dependent on the electron energy and should be at least E(MV)/1.6. The mould contour is created by boolean expansion and subtraction of the shielding. The last design step removes a flat surface of the mould on one end so that the Cerrobend can be poured into the mould but not escape. The mould contour is saved as an .STL file and printed.