SU-G-201-08: Energy Response of Thermoluminescent Microcube Dosimeters in Water for Kilovoltage X-Ray Beams

Abstract

Purpose: To characterize the energy dependence for TLD‐100 microcubes in water at kilovoltage energies. Methods: TLD‐100 microcubes with dimensions of (1 × 1 × 1) mm3 were irradiated with kilovoltage x‐rays in a custom‐built thin‐window liquid water phantom. The TLD‐100 microcubes were held in Virtual Water™ probes and aligned at a 2 cm depth in water. Irradiations were performed using the M‐series x‐ray beams of energies ranging from 50‐250 kVp and normalized to a 60Co beam located at the UWADCL. Simulations using the EGSnrc Monte Carlo Code System were performed to model the x‐ray beams, the 60Co beam, the water phantom and the dosimeters in the phantom. The egs_chamber user code was used to tally the dose to the TLDs and the dose to water. The measurements and calculations were used to determine the intrinsic energy dependence, absorbed‐dose energy dependence, and absorbed‐dose sensitivity. These values were compared to TLD‐100 chips with dimensions of (3.2 × 0.9 × 0.9) mm3. Results: The measured TLD‐100 microcube response per dose to water among all investigated x‐ray energies had a maximum percent difference of 61% relative to 60Co. The simulated ratio of dose to water to the dose to TLD had a maximum percent difference of 29% relative to 60Co. The ratio of dose to TLD to the TLD output had a maximum percent difference of 13% relative to 60Co. The maximum percent difference for the absorbed‐dose sensitivity was 15% more than the used value of 1.41. Conclusion: These results confirm that differences in beam quality have a significant effect on TLD response when irradiated in water. These results also indicated a difference in TLD‐100 response between microcube and chip geometries. The intrinsic energy dependence and the absorbed‐dose energy dependence deviated up to 10% between TLD‐100 microcubes and chips.