PTW-Freiburg, Freiburg D-79115, Germany.
University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University Oldenburg, D-26121, Germany.
Phys Med Biol. 2022 Mar 21;67(7). doi: 10.1088/1361-6560/ac594e.
With increasing investigation of the so-called FLASH effect, the need for accurate real time dosimetry for ultra-high dose rates is also growing. Considering the ultra-high dose-per-pulse (DPP) necessary to produce the ultra-high dose rates for investigations of the FLASH effect, real time dosimetry is a major challenge. In particular, vented ionization chambers, as used for dosimetry in conventional radiotherapy, show significant deviations from linearity with increasing DPP. This is due to recombination losses in the sensitive air volume. Solid state detectors could be an alternative. Due to their good stability of the response with regard to the accumulated dose, diamond detectors such as the microDiamond could be suitable here. The aims of this work are to investigate the response of microDiamond and adapted microDiamond prototypes in ultra-high DPP electron beams, to understand the underlying effects and to draw conclusions for further detector developments.For the study, an electron beam with a DPP up to 6.5 Gy and a pulse duration of 2.5s was used to fulfill the conditions under which the FLASH effect was observed. As a dose rate-independent reference, alanine dosimeters were used.It has been shown that the commercially available microDiamond detectors have limitations in terms of linearity at ultra-high DPP. But this is not an intrinsic limitation of the detector principle. The deviations from linearity were correlated with the series resistance and the sensitivity. It could be shown that the linear range can be extended towards ultra-high DPP range by reducing the sensitivity in combination with a low series resistance of the detectors.The work shows that synthetic single crystal diamond detectors working as Schottky photodiodes are in principle suitable for FLASH-RT dosimetry at electron linear accelerators.
随着对所谓的 FLASH 效应的研究不断深入，对超高剂量率的精确实时剂量测量的需求也在不断增长。考虑到为研究 FLASH 效应而产生超高剂量率所需的超高脉冲剂量（DPP），实时剂量测量是一个主要挑战。特别是，用于常规放射治疗剂量测量的通风电离室在 DPP 增加时会表现出明显的线性偏离。这是由于敏感空气体积中的复合损失所致。固态探测器可能是一种替代方案。由于其对累积剂量的响应稳定性较好，因此诸如 microDiamond 之类的金刚石探测器可能在这里是合适的。这项工作的目的是研究 microDiamond 和经过适配的 microDiamond 原型在超高 DPP 电子束中的响应，以了解潜在的影响，并为进一步的探测器开发得出结论。
在这项研究中，使用了 DPP 高达 6.5Gy 且脉冲持续时间为 2.5s 的电子束，以满足观察 FLASH 效应的条件。作为剂量率无关的参考，使用了丙氨酸剂量计。
研究表明，市售的 microDiamond 探测器在超高 DPP 时的线性度方面存在局限性。但这不是探测器原理的固有限制。线性度的偏差与串联电阻和灵敏度有关。研究结果表明，通过降低探测器的灵敏度并结合低串联电阻，可以将线性范围扩展到超高 DPP 范围。
这项工作表明，作为肖特基光电二极管工作的合成单晶金刚石探测器原则上适用于电子直线加速器的 FLASH-RT 剂量测量。
