Paper Proffered Program Therapy Physics

In-Pulse Dose Rate Effects on Tld-100 Response: A Five-Order-of-Magnitude Proton Study

Abstract

Purpose

To characterize TLD-100 (LiF:Mg,Ti) detector response to synchrotron-based therapeutic proton beams across in-pulse dose rates spanning 0.1 to 2,000 Gy/s.

Methods

TLD-100 powder capsules were irradiated in the entrance region of 87.2 MeV protons using two Hitachi ProBeat synchrotron beamlines: a clinical spot-scanning beamline (0.3 Gy/s in-pulse) and an experimental beamline (0.1-2,000 Gy/s). Three dose levels (3, 9, and 18 Gy) were evaluated across three experimental sessions. Expected doses to TLDs were calculated using benchmarked Geant4 Monte Carlo models. In-pulse dose rates were determined from dose per pulse divided by pulse duration. Pulse duration was measured using an oscilloscope for all dose rates. For dose rates ≤375 Gy/s, dose per pulse was measured using an Advanced Markus ion chamber (Pion = 1.003, ≥99% saturation). For dose rates exceeding the chamber's range, dose per pulse was calculated using Geant4. TLD response was defined as measured-to-expected dose ratio. Positioning at the entrance region isolated dose-rate effects from linear energy transfer (LET)-dependent variations.

Results

TLD response demonstrated systematic in-pulse dose-rate dependence with three distinct regions. At in-pulse dose rates below 7 Gy/s, TLDs exhibited 1-7% over-response attributed to efficient charge carrier trapping. Near-unity response (0-5%) was observed between 7-300 Gy/s, representing balanced trapping and recombination. Above 300 Gy/s, TLDs showed 1-7% under-response due to enhanced electron-hole recombination. Two-way ANOVA confirmed in-pulse dose rate as the dominant factor (82.9% of variance, p 0.05), confirming dose independence across 3-18 Gy.

Conclusion

TLD-100 response to proton beams is dose-independent across 3-18 Gy but follows a characteristic in-pulse dose-rate profile governed by charge carrier dynamics: over-response between 0.1-7 Gy/s, nearly unity between 7-300 Gy/s, and under-response between 300-2,000 Gy/s.

People

Jason TangAuthors · Department of Statistics and Data Sciences, The University of Texas at Austin Jacob MathewAuthors · Department of Biology, University of Houston Fada GuanAuthors · Department of Radiation Physics, The University of Texas MD Anderson Cancer Center Sabrina Campelo, PhD, MSPresenting Author · Department of Radiation Physics, The University of Texas MD Anderson Cancer Center Ivan VazquezAuthors · Department of Radiation Physics, The University of Texas MD Anderson Cancer Center Hayden Scott, MS, BSAuthors · Department of Radiation Physics, The University of Texas MD Anderson Cancer Center Yuting Li, PhDCorrespondings · Department of Radiation Physics, The University of Texas MD Anderson Cancer Center Lawrence F. Bronk, PhDAuthors · Department of Radiation Physics, The University of Texas MD Anderson Cancer Center Paige A. Taylor, PhD, MSAuthors · Imaging and Radiation Oncology Core (IROC) Houston Quality Assurance Center, The University of Texas MD Anderson Cancer Center Ally BrookerAuthors · Department of Physics and Astronomy, Texas A&M University Daniel LiuAuthors · Department of Physics, Yale University