Institute of Radiation Physics, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland.
Radio-Oncology Department, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland.
Radiat Res. 2020 Dec 1;194(6):573-579. doi: 10.1667/RR15568.1.
FLASH radiation therapy (FLASH-RT) reference dosimetry to obtain traceability, repeatability and stability of irradiations cannot be performed with conventional dosimetric methods, such as monitor chambers or ionization chambers. Until now, only passive dosimeters have provided the necessary dosimetric data. Alanine dosimetry is accurate; however, to be used for FLASH-RT in biological experiments and for clinical transfer to humans, the reading time needs to be reduced, while preserving a maximum deviation to the reference of ±2%. Optimization of alanine dosimetry was based on the acquisition of electron paramagnetic resonance (EPR) spectra with a Bruker spectrometer. Reading parameters such as the conversion time, the number of scans, the time constant, the microwave power and the modulation amplitude of the magnetic field were optimized as a trade-off between the signal-to-noise ratio (SNR) and the reading time of one measurement using the reference 10.1 Gy alanine pellet. After optimizing the parameters, we compared the doses measured with alanine pellets up to 100 Gy with the reference doses, and then determined the number of measurements necessary to get a difference lower than ±2%. A low-dose alanine pellet of 4.9 Gy was also measured to evaluate the quality of the optimization for doses lower than 10 Gy. The optimization of the Bruker default parameters made it possible to reduce the reading time for one measurement from 5.6 to 2.6 min. That reduction was not at the cost of the SNR because it was kept comparable to the default parameters. Three measurements were enough to obtain a maximum dose deviation to the reference of 1.8% for the range of 10-100 Gy. The total reading time for the three measurements was 7.8 min (3 × 2.6 min). For lower doses such as 4.9 Gy, three measurements led to a deviation greater than 5%. By increasing the number of measurements to five, the average difference to the reference dose was reduced to less than 5% with a total reading time increased to 13.0 min. For doses between 10 Gy and 100 Gy, the optimized acquisition parameters made it possible to keep the average differences between the reference and the measured doses below ±2%, for a reading time of 7.8 min. This enabled an accurate and fast dose determination for biological preparations as part of FLASH-beam irradiations.
FLASH 放射治疗（FLASH-RT）参考剂量测定不能使用常规剂量测定方法（例如剂量计或电离室）来进行溯源、重复性和稳定性验证。到目前为止，只有无源剂量计提供了必要的剂量数据。丙氨酸剂量测定准确；然而，为了将其用于生物实验中的 FLASH-RT 以及向人类临床转移，需要减少读取时间，同时将最大偏差保持在参考值的±2%以内。丙氨酸剂量测定的优化是基于使用 Bruker 光谱仪获取电子顺磁共振（EPR）谱。作为信噪比（SNR）和使用参考 10.1 Gy 丙氨酸球测量一次的读取时间之间的折衷，优化了转换时间、扫描次数、时间常数、微波功率和磁场调制幅度等读取参数。优化参数后，我们将用丙氨酸球测量的高达 100 Gy 的剂量与参考剂量进行了比较，然后确定了获得低于±2%差异所需的测量次数。还测量了低剂量的 4.9 Gy 丙氨酸球，以评估低于 10 Gy 剂量的优化质量。Bruker 默认参数的优化使得一次测量的读取时间从 5.6 分钟减少到 2.6 分钟。这种减少并不是以 SNR 为代价的，因为它与默认参数相比保持可比。对于 10-100 Gy 的范围，进行三次测量就足以使最大剂量偏差相对于参考值的偏差达到 1.8%。三次测量的总读取时间为 7.8 分钟（3×2.6 分钟）。对于 4.9 Gy 等较低剂量，三次测量导致的偏差大于 5%。通过将测量次数增加到五次，将参考剂量的平均差异降低到 5%以下，总读取时间增加到 13.0 分钟。对于 10 Gy 至 100 Gy 之间的剂量，优化的采集参数使得能够将参考剂量和测量剂量之间的平均差异保持在±2%以下，读取时间为 7.8 分钟。这使得在作为 FLASH 束照射一部分的生物制剂中能够进行准确和快速的剂量测定。
