Farr J B, Moskvin V, Lukose R C, Tuomanen S, Tsiamas P, Yao W
Department of Radiation Oncology, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN, 38105-2794, USA.
Med Phys. 2018 Jul 15. doi: 10.1002/mp.13093.
To invent, design, construct, and commission an intensity modulated minibeam proton therapy system (IMMPT) without the need for physical collimation and to compare its resulting conformity to a conventional IMPT system.
A proton therapy system (Hitachi, Ltd, Hitachi City, Japan; Model: Probeat-V) was specially modified to produce scanned minibeams without collimation. We performed integral depth dose acquisitions and calibrations using a large diameter parallel-plate ionization chamber in a scanning water phantom (PTW, Freiburg, Germany; Models: Bragg Peak ionization chamber, MP3-P). Spot size and shape was measured using radiochromic film (Ashland Advanced Materials, Bridgewater NJ; Type: EBT3), and a synthetic diamond diode type scanned point by point in air (PTW Models: MicroDiamond, MP3-P). The measured data were used as inputs to generate a Monte Carlo-based model for a commercial radiotherapy planning system (TPS) (Varian Medical Systems, Inc., Palo Alto, CA; Model: Eclipse v13.7.15). The regular ProBeat-V system (sigma ~2.5 mm) TPS model was available for comparison. A simulated base of skull case with small and medium targets proximal to brainstem was planned for both systems and compared.
The spot sigma is determined to be 1.4 mm at 221 MeV at the isocenter and below 1 mm at proximal distances. Integral depth doses were indistinguishable from the standard spot commissioning data. The TPS fit the spot profiles closely, giving a residual error maximum of 2.5% in the spot penumbra tails (below 5% of maximum) from the commissioned energies 69.4 to 221.3 MeV. The resulting IMMPT plans were more conformal than the IMPT plans due to a sharper dose gradient (90-10%) 1.5 mm smaller for the small target, and 1.3 mm for the large target, at a representative central axial water equivalent depth of 7 cm.
We developed, implemented, and tested a new IMMPT system. The initial results look promising in cases where treatments can benefit from additional dose sparing to neighboring sensitive structures.
发明、设计、构建并调试一种无需物理准直的调强微束质子治疗系统（IMMPT），并将其产生的适形性与传统调强质子治疗（IMPT）系统进行比较。
对一台质子治疗系统（日本日立市日立有限公司；型号：Probeat-V）进行特殊改装，以产生无准直的扫描微束。我们在扫描水模体（德国弗莱堡PTW；型号：布拉格峰电离室、MP3-P）中使用大直径平行板电离室进行了积分深度剂量采集和校准。使用放射变色胶片（新泽西州布里奇沃特阿什兰先进材料公司；型号：EBT3）测量光斑尺寸和形状，并在空气中逐点扫描合成金刚石二极管类型（PTW型号：MicroDiamond、MP3-P）。测量数据用作商业放射治疗计划系统（TPS）（加利福尼亚州帕洛阿尔托瓦里安医疗系统公司；型号：Eclipse v13.7.15）基于蒙特卡洛模型的输入。常规ProBeat-V系统（σ~2.5毫米）TPS模型可用于比较。为两个系统规划并比较了一个模拟的靠近脑干的中小靶区的颅底病例。
在等中心处，221 MeV时光斑σ确定为1.4毫米，在近端距离处低于1毫米。积分深度剂量与标准光斑调试数据无明显差异。TPS与光斑轮廓拟合紧密，在69.4至221.3 MeV的调试能量下，光斑半影尾部（低于最大值的5%）的残余误差最大为2.5%。在7厘米的代表性中心轴水等效深度处，由于小靶区的剂量梯度更陡（90-10%），小靶区小1.5毫米，大靶区小1.3毫米，因此产生的IMMPT计划比IMPT计划更适形。
我们开发、实施并测试了一种新的IMMPT系统。在治疗可受益于对相邻敏感结构额外的剂量 sparing的情况下，初步结果看起来很有前景。
