Langner Ulrich W, Eley John G, Dong Lei, Langen Katja
Department of Radiation Oncology, Maryland Proton Treatment Center, University of Maryland School of Medicine, 850 W. Baltimore Street, Baltimore, MD, 21201, USA.
Scripps Proton Therapy Center, 9730 Summers Ridge Road, San Diego, CA, 92121, USA.
J Appl Clin Med Phys. 2017 May;18(3):96-107. doi: 10.1002/acm2.12078. Epub 2017 Apr 19.
Commissioning beam data for proton spot scanning beams are compared for the first two Varian ProBeam sites in the United States, at the Maryland Proton Treatment Center (MPTC) and Scripps Proton Therapy Center (SPTC). In addition, the extent to which beams can be matched between gantry rooms at MPTC is investigated.
Beam data for the two sites were acquired with independent dosimetry systems and compared. Integrated depth dose curves (IDDs) were acquired with Bragg peak ion chambers in a 3D water tank for pencil beams at both sites. Spot profiles were acquired at different distances from the isocenter at a gantry angle of 0° as well as a function of gantry angles. Absolute dose calibration was compared between SPTC and the gantries at MPTC. Dosimetric verification of test plans, output as a function of gantry angle, monitor unit (MU) linearity, end effects, dose rate dependence, and plan reproducibility were compared for different gantries at MPTC.
The IDDs for the two sites were similar, except in the plateau region, where the SPTC data were on average 4.5% higher for lower energies. This increase in the plateau region decreased as energy increased, with no marked difference for energies higher than 180 MeV. Range in water coincided for all energies within 0.5 mm. The sigmas of the spot profiles in air were within 10% agreement at isocenter. This difference increased as detector distance from the isocenter increased. Absolute doses for the gantries measured at both sites were within 1% agreement. Test plans, output as function of gantry angle, MU linearity, end effects, dose rate dependence, and plan reproducibility were all within tolerances given by TG142.
Beam data for the two sites and between different gantry rooms were well matched.
对美国最初的两个瓦里安质子束扫描治疗系统（Varian ProBeam）的调试束流数据进行比较，这两个系统分别位于马里兰质子治疗中心（MPTC）和斯克里普斯质子治疗中心（SPTC）。此外，还研究了MPTC不同机架室之间束流的匹配程度。
使用独立的剂量测定系统获取两个治疗中心的束流数据并进行比较。在两个治疗中心，均使用布拉格峰电离室在三维水箱中获取笔形束的积分深度剂量曲线（IDDs）。在机架角度为0°时，在距等中心不同距离处以及作为机架角度的函数获取束斑轮廓。比较了SPTC与MPTC各机架的绝对剂量校准。针对MPTC的不同机架，比较了测试计划的剂量学验证、作为机架角度函数的输出剂量、监测单位（MU）线性、端部效应、剂量率依赖性和计划可重复性。
两个治疗中心的IDDs相似，但在坪区有所不同，较低能量时SPTC的数据平均高4.5%。随着能量增加，坪区的这种增加幅度减小，能量高于180 MeV时无明显差异。水中射程在所有能量下的重合度在0.5 mm以内。等中心处空气中束斑轮廓的标准差一致性在10%以内。随着探测器与等中心距离增加，这种差异增大。两个治疗中心测量的各机架绝对剂量一致性在1%以内。测试计划、作为机架角度函数的输出剂量、MU线性、端部效应、剂量率依赖性和计划可重复性均在TG142规定的公差范围内。
两个治疗中心以及不同机架室之间的束流数据匹配良好。
