FLASH Radiotherapy and the Use of Radiation Dosimeters

SIMPLE SUMMARY: FLASH radiotherapy (RT) delivering ultra-high dose rate radiation can reduce normal tissue toxicity while effectively treating tumors. However, implementing FLASH RT in clinical settings faces challenges like limited depth penetration and complex treatment planning. Monte Carlo simulation is a valuable tool to optimize FLASH RT. Radiation detectors, including diamond detectors like microDiamond and ionization chambers, play a crucial role in accurately measuring dose delivery. Moreover, optically stimulated luminescence dosimeters and radiochromic films are used for validation. Advancements are being made to improve detector accuracy in FLASH RT. Further research is needed to refine treatment planning and detector performance for widespread FLASH RT implementation, which can potentially revolutionize cancer treatment. ABSTRACT: Radiotherapy (RT) using ultra-high dose rate (UHDR) radiation, known as FLASH RT, has shown promising results in reducing normal tissue toxicity while maintaining tumor control. However, implementing FLASH RT in clinical settings presents technical challenges, including limited depth penetration and complex treatment planning. Monte Carlo (MC) simulation is a valuable tool for dose calculation in RT and has been investigated for optimizing FLASH RT. Various MC codes, such as EGSnrc, DOSXYZnrc, and Geant4, have been used to simulate dose distributions and optimize treatment plans. Accurate dosimetry is essential for FLASH RT, and radiation detectors play a crucial role in measuring dose delivery. Solid-state detectors, including diamond detectors such as microDiamond, have demonstrated linear responses and good agreement with reference detectors in UHDR and ultra-high dose per pulse (UHDPP) ranges. Ionization chambers are commonly used for dose measurement, and advancements have been made to address their response nonlinearities at UHDPP. Studies have proposed new calculation methods and empirical models for ion recombination in ionization chambers to improve their accuracy in FLASH RT. Additionally, strip-segmented ionization chamber arrays have shown potential for the experimental measurement of dose rate distribution in proton pencil beam scanning. Radiochromic films, such as Gafchromic(TM) EBT3, have been used for absolute dose measurement and to validate MC simulation results in high-energy X-rays, triggering the FLASH effect. These films have been utilized to characterize ionization chambers and measure off-axis and depth dose distributions in FLASH RT. In conclusion, MC simulation provides accurate dose calculation and optimization for FLASH RT, while radiation detectors, including diamond detectors, ionization chambers, and radiochromic films, offer valuable tools for dosimetry in UHDR environments. Further research is needed to refine treatment planning techniques and improve detector performance to facilitate the widespread implementation of FLASH RT, potentially revolutionizing cancer treatment.