■质子小束放射治疗(pMBRT)可以以亚毫米分辨率提供空间分割的剂量分布。这些剂量分布在深度和横向方向上都表现出明显的异质性。pMBRT剂量的准确表征需要具有高空间分辨率和宽动态范围的剂量测定装置。此外,剂量测定测量对线性能量转移(LET)的依赖性,正如在常规质子治疗中观察到的那样,也存在于pMBRT深度剂量测量中。
■这项工作演示了在临床单龙门质子机上进行全面的剂量学测量以表征pMBRT准直器的过程,利用市售的剂量测定装置。
■微型光束准直器设计为作为光束修改附件安装在临床喷嘴上。三个准直器,每个都有0.4毫米的狭缝开口,经过全面评估。这些准直器的狭缝的中心到中心(c-t-c)距离为2.8mm,3.2mm,和4.0毫米,分别。高空间分辨率剂量测定设备对于PMBRT剂量表征至关重要。为了满足这一要求,二维(2D)剂量测量装置,Gafchrome胶片,用于测量不同深度的横向剖面。薄膜也用于固体水中的深度剂量分布测量。此外,高分辨率点剂量探测器,microDiamond,和剃刀二极管检测器用于各种深度的横向轮廓测量。固体水中pMBRT的深度剂量百分比(PDD)测量值,各种质子能量,准直器,和气隙,使用Gafchrome胶片进行。校正了薄膜对质子束的LET依赖性,以确保精确的pMBRTPDD测量。蒙特卡罗模拟工具TOPAS用于比较和验证所有实验测量。
■在不关心LET的深度,膜剂量测量与微金刚石和剃刀二极管点测量一致。点检测器需要在薄侧与入射光束对准的情况下进行定向。比较从TOPAS模拟中提取的侧向剂量分布,电影,microDiamond,和Razor二极管检测器在3%0.1mm标准下的1D伽马分析中显示出超过98%的通过率。然而,当microDiamond探测器朝向pMBRT光束时,其空间分辨率可能不足以准确捕获峰谷剂量。然而,在比较平均剂量时,仍可达到2%以内的准确度。PDD测量表明,可以使用相同的准直器或不同的c-t-c距离的不同准直器,在具有不同气隙的不同深度处改变pMBRT的峰谷剂量比(PVDR)。
■我们的研究表明,可以使用标准临床剂量测量设备进行pMBRT的全面剂量测量。这些测量对于使用pMBRT技术指导和确保临床前研究中的准确剂量报告是必不可少的。
UNASSIGNED: Proton minibeam radiation therapy (pMBRT) can deliver spatially fractionated dose distributions with submillimeter resolution. These dose distributions exhibit significant heterogeneity in both depth and lateral directions. Accurate characterization of pMBRT doses requires dosimetry devices with high spatial resolution and a wide dynamic range. Furthermore, the dependency of dosimetric measurements on Linear Energy Transfer (LET), as observed in conventional proton therapy, is also present in pMBRT depth dose measurements.
UNASSIGNED: This work demonstrates the process of performing comprehensive dosimetric measurements to characterize the pMBRT collimator on a clinical single-gantry proton machine, utilizing commercially available dosimetry devices.
UNASSIGNED: The minibeam collimator is designed to be mounted on the clinical nozzle as a beam-modifying accessory. Three collimators, each with a slit opening of 0.4 mm, are thoroughly evaluated. The center-to-center (c-t-c) distances of the slits for these collimators are 2.8 mm, 3.2 mm, and 4.0 mm, respectively. High spatial resolution dosimetry devices are essential for PMBRT dose characterizations. To meet this requirement, two-dimensional (2D) dose measurement devices, Gafchromic films, are used to measure lateral profiles at various depths. Films are also used for depth dose profile measurements in solid water. Additionally, high-resolution point dose detectors, microDiamond, and Razor diode detectors are employed for lateral profile measurements at various depths. Percent depth dose (PDD) measurements of pMBRT in solid water, with various proton energies, collimators, and air gaps, are performed using Gafchromic films. The film\'s LET dependency for proton beams is corrected to ensure accurate pMBRT PDD measurements. The Monte Carlo simulation tool TOPAS is utilized to compare and validate all experimental measurements.
UNASSIGNED: At depths where LET is not a concern, film dose measurements were consistent with microDiamond and Razor diode point measurements. The point detectors need to be orientated with the thin side aligned to the incoming beam. Comparison of the lateral dose profiles extracted from TOPAS simulations, films, microDiamond, and Razor diode detectors shows a passing rate exceeding 98% in 1D gamma analysis at 3% 0.1 mm criteria.However, when the microDiamond detector is orientated to face the pMBRT beam, its spatial resolution may not be sufficient to capture the peak and valley dose accurately. Nevertheless, an accuracy within 2% can still be achieved when comparing the average dose. The PDD measurements show that the peak valley dose ratio (PVDR) of pMBRT can be altered at different depths with different air gaps using the same collimator or different collimators of different c-t-c distances.
UNASSIGNED: Our study demonstrates that comprehensive dose measurements for pMBRT can be conducted using standard clinical dose measurement devices. These measurements are indispensable for guiding and ensuring accurate dose reporting in pre-clinical studies using the pMBRT technique.