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  5. Effect of a 1.4 T Magnetic Field On TLDs with a 6MV Medical Linear Accelerator

Effect of a 1.4 T Magnetic Field On TLDs with a 6MV Medical Linear Accelerator

W Culberson1*, W Culberson2 , C Hammer3 , R Kapsch4 , U Ankerhold5 , (1) university of Wisc Madison, Department of Medical Physics, School of Medicine and Public Health, Madison, WI, (2) university of Wisc Madison, Department of Medical Physics, School of Medicine and Public Health, Madison, WI, (3) University of Wisconsin Madison, Madison, Wisconsin, (4) Physikalisch Technische Bundesanstalt, Braunschweig, Germany (5) Physikalisch Technische Bundesanstalt, Braunschweig, Germany

Presentations

(Sunday, 7/29/2018) 4:00 PM - 4:55 PM

Room: Karl Dean Ballroom A1

Purpose: With the increase in MRI-guided RT delivery platforms, it’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 mm³ and microcubes with dimensions of 1x1x1 mm³. 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.

Keywords

TLDs, Magnetic Fields, Dosimetry

Taxonomy

TH- Radiation dose measurement devices: TLD

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