Detectors in FLASH Radiation Therapy

FLASH radiation therapy (FLASH RT) is an emerging treatment modality that delivers ultra-high dose rate (UHDR) radiation (≳40 Gy/s) in a short duration (≲200 milliseconds). This modality has shown promise in reducing normal tissue toxicity while maintaining tumor control. This technique has garnered considerable interest due to its potential to revolutionize cancer treatment by leveraging the FLASH effect, a phenomenon in which normal tissues exhibit greater sparing while maintaining the same tumor control compared to conventional RT. Although the underlying mechanism(s) are not yet understood, the radiation response data generated so far suggest that the FLASH effect is highly influenced by the radiation beam parameters that are used. A critical aspect of FLASH RT is accurate dosimetry to measure the beam parameters, which presents unique challenges due to the extremely high dose rates and short irradiation times. Consequently, since radiation instruments were previously rarely tested under UHDR conditions, there is a lack of primary standards that are used as a reference for the measurement of ionizing radiation. Traditional dosimetry systems, designed for conventional dose rates (cGy/s), often fail to accurately capture the beam parameters delivered in FLASH RT. Development of modified dosimeters is underway, such as scintillation detectors and ionization chambers adapted for UHDR to enable precise dose measurements and beam monitors capable of monitoring and controlling the beam output in real time. Key challenges in FLASH RT dosimetry include detector response time and addressing signal saturation and recombination effects, all of which impact the accuracy and reproducibility of measurements. These questions are valid for basic dose measurements and for proper beam monitoring with these detectors. Additionally, standardization of dosimetric protocols is essential for clinical translation. As FLASH RT progresses toward clinical implementation, robust dosimetry remains a cornerstone for safe and effective treatments. Overcoming current challenges will facilitate its integration into routine oncology practice. Future studies will further elucidate the biological mechanisms underlying the FLASH effect and refine dosimetric techniques to enhance treatment precision.