Room: Karl Dean Ballroom A1
Purpose: With the increase in MRI-guided RT delivery platforms, itâ€™s important to characterize the change in response of any dosimeter used. For this study, the effect of a magnetic field on the absorbed dose to water response of TLD-100 dosimeters was tested by using water-equivalent plastic probes submerged in a water tank with a bench top magnet capable of creating 1.4 T magnetic fields and a medical linear accelerator installed at the German National Metrology Institute.
Methods: Two different form factors of TLD-100 were used in this experiment including chips with dimensions of 3x3x1 mmÂ³ and microcubes with dimensions of 1x1x1 mmÂ³. The TLDs were enclosed in a water-equivalent plastic probe designed specifically to keep the TLDs waterproof while submerged at a depth of 10 cm in a water tank. A bench top electromagnet with a 1.4 T magnetic field strength was used to apply the magnetic field. A 6MV Elekta Precise linear accelerator at the German National Metrology Institute (PTB) was used to deliver the dose in a horizontal beam line configuration and the dose rates with direct traceability to PTB absorbed dose to water standards. A 60Co source was used to calibrate the sensitivity of each TLD. A total of 120 TLDs were used to determine the change in response with the magnetic field with delivered doses of 2 Gy or 5 Gy.
Results: The results showed a statistically significant under response of TLD-100 of up to 2.3%, with a slightly larger under response for the microcubes. There was not a statistically significant difference in the under response between 2 Gy and 5 Gy irradiations.
Conclusion: The results of this study show a small, but significant, under response of TLD-100 in a 1.4 Tesla magnetic field.