Room: Exhibit Hall | Forum 7
Purpose: For breast Intrabeam (Carl Zeiss Meditec) IORT dose to the bone (ribs) for lumpectomy cavities close to the chest wall is very high as expected for 50 kV X-rays. It can reach 200% of the prescription dose in simulated calculations using the Radiance Monte Carlo based planning system in conjunction with pre-op CT scans. A sterile flexible shield placed between the Intrabeam applicator and the chest wall could protect the ribs from receiving this large unnecessary dose.Unfortunately, shields for protection of critical organs during IORT are currently not commercially available. Two possible materials were evaluated dosimetrically.
Methods: Recently developed tungsten based functional paper (TFP) and XGUARD radiation reducing gloves were evaluated using EBT3 radiochromic film in a specially designed Solid Water phantom placed into a modified Intrabeam water tank (without water) for proper measurement setup and radiation protection. Film was calibrated for absolute dosimetry using a calibrated I-125 seed in a Solid Water calibration phantom and TG-43. Films were irradiated using a 30 mm flat applicator at 4 different depths from 0 to 10 mm from the applicator without any shield or with one or two layers of TFP or XGUARD material.
Results: While the TFP provides superior protection per layer, transmitting 22.8% (single layer) or 7.8% (two layers) at depth 5 mm, it is less flexible and not sterile, compared to the XGUARD glove material, transmitting 41.7% (single layer) or 25.8% (two layers), which is sterile and much more flexible.
Conclusion: Radiochromic film in a Solid Water phantom is a convenient technique for low keV X-ray dosimetry. A calibrated I-125 seed and TG-43 enable film calibration for absolute dosimetry. Both materials can be used for protection of critical organs, but both have to be placed into sterile pouches, since cutting even the sterile glove can leave shreds.
Funding Support, Disclosures, and Conflict of Interest: Partial funding and material support were provided by Carl Zeiss Meditec, Oberkochen, Germany. A calibrated high activity I-125 seed was provided by Eckert & Ziegler BEBIG GmbH, Berlin, Germany.