Saini Jatinder, Erickson Danielle P Johnson, Vander Stappen François, Ruth Matt, Cui Sunan, Gorman Vanessa, Rossomme Séverine, Cao Ning, Ford Eric C, Meyer Juergen, Bloch Charles, Wong Tony, Grassberger Clemens, Rengan Ramesh, Zeng Jing, Schwarz Marco
Department of Radiation Oncology, University of Washington School of Medicine, Seattle, WA, United States.
Radiation Oncology, Fred Hutchinson Cancer Center, Seattle, WA, United States.
Front Oncol. 2024 Nov 29;14:1460288. doi: 10.3389/fonc.2024.1460288. eCollection 2024.
This manuscript describes modifications to a pencil beam scanning (PBS) proton gantry that enables ultra-high dose rates (UHDR) irradiation, including treatment planning and validation.
Beamline modifications consisted of opening the energy slits and setting the degrader to pass-through mode to maximize the dose rate. A range shifter was inserted upstream from the isocenter to enlarge the spot size and make it rotationally symmetric. We measured the beamline transport efficiency and investigated the variation in output due to the recombination of charge in the dose monitoring chamber. The output calibration was performed through a parallel plate chamber (PPC05), and an intercomparison was performed for various detectors. The pre-clinical field for mice irradiation consisted of different dose levels to deliver uniform doses in transmission mode. The field dose rates were determined through log files while scripting in TPS was used to estimate PBS dose rates. The survival experiments consisted of irradiating the full pelvis of the mice at UHDR and conventional dose rates.
The spot size was constant with beam current and had a sigma of 8.5 mm at the isocenter. The beam output increased by 35% at 720 nA compared to 5.6 nA, primarily due to recombination in the dose-monitoring ion chambers. The Faraday Cup and PPC05 agreed within 2%, while other detectors were within 3% of FC for dose rates <60 Gy/s. The pre-clinical fields' PBS dose rate is above 45 Gy/sec for all voxels within the target volume. The average and PBS dose rates decrease as field size increases and approaches 40 Gy/s for a field size of 7x7 cm. All UHDR arms showed better survival than the corresponding conventional dose rate arms.
We successfully modified a clinical system to perform UHDR pre-clinical experiments. As part of our pre-clinical experiments, we observed the FLASH effect concerning mice survival.
本手稿描述了对笔形束扫描（PBS）质子机架的改进，该改进能够实现超高剂量率（UHDR）照射，包括治疗计划和验证。
束线改进包括打开能量狭缝并将降解器设置为穿透模式以最大化剂量率。在等中心上游插入一个射程移位器以扩大光斑尺寸并使其旋转对称。我们测量了束线传输效率，并研究了剂量监测室中电荷复合导致的输出变化。通过平行板电离室（PPC05）进行输出校准，并对各种探测器进行了比对。用于小鼠照射的临床前野由不同剂量水平组成，以在透射模式下提供均匀剂量。通过日志文件确定野剂量率，同时使用TPS脚本估计PBS剂量率。生存实验包括以UHDR和传统剂量率照射小鼠的全骨盆。
光斑尺寸随束流恒定，在等中心处的标准差为8.5毫米。与5.6纳安相比，在720纳安时束输出增加了35%，主要是由于剂量监测离子室中的复合。对于剂量率<60 Gy/s，法拉第杯和PPC05的结果在2%以内一致，而其他探测器与FC的结果在3%以内。目标体积内所有体素的临床前野的PBS剂量率均高于45 Gy/秒。平均和PBS剂量率随野尺寸增加而降低，对于7x7厘米的野尺寸接近40 Gy/s。所有UHDR组的生存率均高于相应的传统剂量率组。
我们成功地对临床系统进行了改进，以进行UHDR临床前实验。作为我们临床前实验的一部分，我们观察到了关于小鼠生存的FLASH效应。
