2022 AAPM 64th Annual Meeting
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Session Title: The Need for Robust Dosimetry of Flash Beams
Question 1: What beam parameters need to be considered when investigating the response of detectors in UHDR beams?
Reference:Schuller et al, “The European Joint Research Project UHDPulse – Metrology for advanced radiotherapy using particle beams with ultra-high pulse dose rates:, Physica Medica, 80 (2020)
Choice A:Dose per pulse
Choice B:Instantaneous dose rate
Choice C:Mean dose rate
Choice D:Pulse width
Choice E:All of the above
Question 2: TG-51 cannot be used for ionization chamber dosimetry in beams where the ion recombination correction factor is greater than 1.05.
Reference:Almond et al, Medical Physics, 1999
Choice A:TRUE
Choice B:FALSE
Question 3: Why are the ionization chambers currently used in clinics not ideal?
Reference:Petersson K, et al. High dose-per-pulse electron beam dosimetry - A model to correct for the ion recombination in the Advanced Markus ionization chamber. Med Phys (2017) 44(3):1157-1167. Di Martino, et al. Ion recombination correction for very high dose-per-pulse high-energy electron beams. Med Phys. (2005) 32(7):2204-10.
Choice A:Because of the long chamber response time with respect to the exposure time
Choice B:Due to ion collection efficiency dependence on dose-per-pulse
Choice C:Due to decrease of ion collection efficiency at high dose rates
Choice D:Due to decrease of ion collection efficiency at low dose rates
Choice E:b & c
Question 4: Which detector(s) are NOT considered to be dose-rate independent?
Reference:Karsch L, et al. Dose rate dependence for different dosimeters and detectors. Med Phys. (2012) 39(5):2447-55.
Choice A:EBT films
Choice B:Alanine
Choice C:TLDs
Choice D:Calorimeters
Choice E:OSLs
Choice F:Diamond detectors
Question 5: What factors influence the collection efficiency and recombination effects of an ion chamber in a proton FLASH beam?
Reference:E Diffenderfer et al. “The current status of preclinical proton FLASH radiation and future directions”. Med Phys. 2022 Mar;49(3):2039-2054. doi: 10.1002/mp.15276. PMID: 34644403.
Choice A:Pulse structure
Choice B:Bias voltage
Choice C:Electrode separation
Choice D:Ion source current
Choice E:All of the above
Question 6: Which statement about the use of a Faraday Cup in dose validation for FLASH beams is NOT true?
Reference:E Diffenderfer et al. “Design, Implementation, and in Vivo Validation of a Novel Proton FLASH Radiation Therapy System”. Int J Radiat Oncol Biol Phys. 2020 Feb 1;106(2):440-448. doi: 10.1016/j.ijrobp.2019.10.049. PMID: 31928642.
Choice A:Validation of a Faraday Cup for collection efficiency dose rate independence requires the relative comparison of low and high dose rates.
Choice B:Within clinical FLASH range, Faraday Cup dosimetry and parallel plate ion chamber dosimetry agree within 0.5%.
Choice C:Faraday Cup dosimetry is energy dependent and therefore cannot be used across therapeutic proton energy spectrum.
Choice D:A Faraday Cup is essentially a “proton counter” and demonstrates high collection efficiency and low charge lose.
Choice E:All of the above
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