Karle Celine, Verona-Rinati Gianluca, Brons Stephan, Cee Rainer, Scheloske Stefan, Schömers Christian, Kranzer Rafael, Haberer Thomas, Marinelli Marco, Mairani Andrea, Tessonnier Thomas
Clinical Cooperation Unit Translational Radiation Oncology, National Center for Tumor Diseases (NCT), Heidelberg University Hospital (UKHD) and German Cancer Research Center (DKFZ), Heidelberg, Germany.
Department of Physics and Astronomy, Heidelberg University, Heidelberg, Germany.
Med Phys. 2025 Jul;52(7):e17893. doi: 10.1002/mp.17893. Epub 2025 Jun 2.
The emerging FLASH radiotherapy technique employs "Ultra-High Dose Rate" (UHDR) irradiations and offers the potential to spare normal tissue while maintaining iso-effective tumor treatment. Given the physical and biological advantages inherent to high "Linear Energy Transfer" (LET) particles, the combination of UHDR and high LET has the capability to enhance the normal tissues sparing, as indicated by initial in vivo trials. However, to ensure a safe implementation of this combined modality, it is essential to establish robust dosimetric protocols utilizing dose-, dose rate-, and LET-independent detectors.
The objective of this study is to characterize the dose, dose rate, and LET dependency of two diamond detectors with high LET carbon and oxygen ion irradiation under "Standard Dose Rate" (SDR) and UHDR conditions.
The "microDiamond" (mD) and a "flashDiamond" (fD) prototype were benchmarked against measurements with a monitoring ionization chamber, Advanced Markus chamber (AMC), and simulations for carbon and oxygen irradiation, with energies of 274.98 MeV/u and 325.98 MeV/u under SDR and UHDR conditions. First, the entire depth-dose profiles obtained during SDR irradiations and the partial in-depth profiles of the Bragg peak region in UHDR were compared to the corresponding simulation values. Secondly, the linearity of the diamond detector response during dose escalation measurements was investigated for both dose rates.
The two detectors exhibited alignment with the simulated depth-dose distributions for oxygen and carbon irradiations across both dose rate conditions. The mD overestimated the dose values for carbon and oxygen measurements. This overestimation increased with "dose-averaged LET" (LETd) during SDR irradiation and maintained a stable value of 5% for UHDR. Meanwhile, the fD demonstrated a high degree of agreement with the simulation, with a maximum discrepancy of 5% across all irradiation modalities in the plateau and "Bragg Peak" (BP). Deviations were observed in the BP fall-off region, while both diamond detectors exhibited a strong alignment with the AMC measurements. Furthermore, both detectors exhibited dose linearity under SDR and UHDR irradiation for both carbon and oxygen irradiation, with a coefficient of determination (R) above 0.99.
In the context of heavy ion carbon and oxygen irradiation in UHDR and SDR, the two diamond detectors demonstrated dose-rate independence. While the mD exhibited a tendency to overestimate dose values with increasing LETd, the fD was found to be LET-independent. The fD appears to offer accurate and reliable dose assessments for UHDR heavy ion experiments.
新兴的FLASH放疗技术采用“超高剂量率”（UHDR）照射，有望在维持肿瘤等效治疗的同时保护正常组织。鉴于高“线能量转移”（LET）粒子固有的物理和生物学优势，如初步体内试验所示，UHDR与高LET相结合有能力增强对正常组织的保护。然而，为确保这种联合模式的安全实施，利用与剂量、剂量率和LET无关的探测器建立稳健的剂量测定方案至关重要。
本研究的目的是在“标准剂量率”（SDR）和UHDR条件下，表征两种金刚石探测器在高LET碳离子和氧离子照射下的剂量、剂量率和LET依赖性。
“微型金刚石”（mD）和“闪光金刚石”（fD）原型与监测电离室、高级马库斯室（AMC）的测量结果以及碳离子和氧离子照射的模拟结果进行了基准对比，在SDR和UHDR条件下，碳离子和氧离子的能量分别为274.98 MeV/u和325.98 MeV/u。首先，将SDR照射期间获得的完整深度剂量分布以及UHDR中布拉格峰区域的部分深度分布与相应的模拟值进行比较。其次，研究了两种剂量率下剂量递增测量期间金刚石探测器响应的线性度。
在两种剂量率条件下，两种探测器在氧离子和碳离子照射的模拟深度剂量分布方面表现出一致性。mD高估了碳离子和氧离子测量的剂量值。在SDR照射期间，这种高估随着“剂量平均LET”（LETd）增加，而在UHDR中保持5%的稳定值。同时，fD与模拟结果高度吻合，在坪区和“布拉格峰”（BP）的所有照射模式下最大差异为5%。在BP下降区域观察到偏差，而两种金刚石探测器与AMC测量结果表现出很强的一致性。此外，在SDR和UHDR照射下，两种探测器在碳离子和氧离子照射时均表现出剂量线性，决定系数（R）高于0.99。
在UHDR和SDR的重离子碳离子和氧离子照射背景下，两种金刚石探测器表现出剂量率独立性。虽然mD表现出随着LETd增加高估剂量值的趋势，但发现fD与LET无关。fD似乎为UHDR重离子实验提供了准确可靠的剂量评估。
