Gonçalves Jorge Patrik, Geyer Reiner, Kinj Rémy, Schiappacasse Luis, Jeanneret-Sozzi Wendy, Bourhis Jean, Herrera Fernanda, Bochud François, Bailat Claude, Moeckli Raphaël
Institute of Radiation Physics, Lausanne University Hospital and Lausanne University, Lausanne, Switzerland.
Department of Radiation Oncology, Lausanne University Hospital and Lausanne University, Lausanne, Switzerland.
J Appl Clin Med Phys. 2025 Jun;26(6):e70102. doi: 10.1002/acm2.70102. Epub 2025 Apr 10.
The FLASH effect, induced by ultra-high dose rate (UHDR) irradiations, offers the potential to spare normal tissue while effectively treating tumors. It is important to achieve precise and accurate dose delivery and to establish reliable detector systems, particularly for clinical trials needed to help the clinical transfer of FLASH-Radiotherapy (FLASH-RT). However, the use of monitoring chambers with UHDR beams is presently limited, leading to the reliance on passive dosimetry and machine stability.
This study aimed to investigate the energy and output stability of a UHDR Mobetron (IntraOp, USA) and to compare it with its conventional dose rate (CDR) mode. Furthermore, we assessed the dosimetric accuracy of a human clinical protocol for FLASH-RT.
Over a 26-month duration, we assessed the short- and long-term stability of the output and energy of the Mobetron system. Daily checks were conducted for 9 MeV CDR and UHDR. In parallel, the IMPulse clinical trial involving patients with skin metastases from melanoma was initiated. Prescription doses ranging from 22 to 28 Gy were administered. Pre-, post-, and in vivo dosimetry using alanine and thermoluminescent dosimeters (TLDs) was performed and compared to the prescription doses.
Short-term output fluctuations remained below 0.6 % and 1 % for 9 MeV CDR and UHDR, respectively. Long-term output fluctuations were within 2 % and the long-term energy fluctuations were below 2 mm (R) for both modes. The delivered doses of the IMPulse trial showed deviations below 4 % compared to prescription doses for all patients.
The Mobetron system demonstrated favorable short- and long-term stability. There was a good agreement between the prescribed and the measured dose for the clinical IMPulse trial. The stability of this UHDR machine allows us to effectively conduct human clinical protocols as well as preclinical experiments, even in the absence of a real-time monitoring system.
超高剂量率（UHDR）照射所引发的“FLASH效应”，为在有效治疗肿瘤的同时保护正常组织提供了可能。实现精确且准确的剂量输送以及建立可靠的探测器系统至关重要，特别是对于助力FLASH放射治疗（FLASH-RT）临床应用转化所需的临床试验而言。然而，目前使用监测腔室对UHDR射束进行监测存在限制，这导致对被动剂量测定法和机器稳定性的依赖。
本研究旨在探究UHDR型Mobetron（美国IntraOp公司）的能量及输出稳定性，并将其与传统剂量率（CDR）模式进行比较。此外，我们评估了一项FLASH-RT人体临床方案的剂量测定准确性。
在26个月的时间里，我们评估了Mobetron系统输出和能量的短期及长期稳定性。对9 MeV的CDR和UHDR进行每日检查。与此同时，启动了涉及黑色素瘤皮肤转移患者的IMPulse临床试验。给予的处方剂量范围为22至28 Gy。使用丙氨酸和热释光剂量计（TLD）进行术前、术后及体内剂量测定，并与处方剂量进行比较。
9 MeV的CDR和UHDR的短期输出波动分别保持在0.6%和1%以下。两种模式的长期输出波动均在2%以内，长期能量波动均低于2 mm（R）。IMPulse试验中所有患者的实际给药剂量与处方剂量相比偏差均低于4%。
Mobetron系统展现出良好的短期和长期稳定性。在IMPulse临床研究中，处方剂量与测量剂量之间具有良好的一致性。即便没有实时监测系统，这种UHDR机器的稳定性也使我们能够有效地开展人体临床方案以及临床前实验。
