Slopsema R, Mamalui-Hunter M, Yeung D, Li Z
University of Florida, Jacksonville, FL.
Med Phys. 2012 Jun;39(6Part14):3771-3772. doi: 10.1118/1.4735378.
To commission a proton-therapy system for the treatment of uveal melanoma and age-related macular degeneration.
Proton therapy system is the proto-type of a commercial product developed by Ion Beam Applications. Proton beam is brought into the treatment room at 105 MeV through a fixed beam line. A single-scattering system with absorber/scattering foils spreads the beam into a Gaussian profile. A library of 10 range-modulator wheels and 16 range-modulator blocks generate spread-out Bragg peaks of various range and modulation width. Source-to-axis distance of the system is 169 cm. Two orthogonal digital x-ray panels are used for alignment. EyePlan software is used both for both treatment planning and in-room alignment.
Range can be varied continuously between 0.5 and 3.4 g/cm . Range accuracy is measured to be better than 0.05 g/cm . Modulation width can be varied in steps of =0.3 g/cm with an accuracy of 0.05 g/cm or 2%. Maximum aperture diameter is 2.5 cm and maximum dose rate >32 Gy/min. Strong dependence of output on range (7%/mm) and dose rate (0.2%/(Gy/min)) is found. Distal and lateral fall-off (80%-20%) are =0.23 and =0.18 g/cm and do not depend much on range or depth. When reducing the aperture diameter to 6 mm no significant change is observed in shape of depth-dose curve or absolute dose (<2.5%). Measurements show a significant portion of the dose at shallow depth (=0.7 g/cm ) is delivered by protons scattering off of snout elements. Simple collimation could reduce this effect.
The dosimetric and positioning properties of the IBA ocular proton system are adequate to treat ocular lesions with acceptable clinical margins. Suggested improvements include limiting the output-dependence on range and reducing snout scatter.
启用一套质子治疗系统，用于治疗葡萄膜黑色素瘤和年龄相关性黄斑变性。
质子治疗系统是离子束应用公司研发的一款商用产品的原型。质子束通过固定束线以105兆电子伏特的能量进入治疗室。带有吸收体/散射箔的单散射系统将束流扩散成高斯分布。一个由10个射程调制轮和16个射程调制块组成的库可产生各种射程和调制宽度的扩展布拉格峰。该系统的源轴距为169厘米。使用两块正交数字X射线平板进行对准。EyePlan软件用于治疗计划和室内对准。
射程可在0.5至3.4克/立方厘米之间连续变化。测量得到的射程精度优于0.05克/立方厘米。调制宽度可按0.3克/立方厘米的步长变化，精度为0.05克/立方厘米或2%。最大孔径直径为2.5厘米，最大剂量率>32戈瑞/分钟。发现输出对射程（7%/毫米）和剂量率（0.2%/（戈瑞/分钟））有很强的依赖性。远端和侧向剂量下降（80%-20%）分别为=0.23和=0.18克/立方厘米，且对射程或深度的依赖性不大。当将孔径直径减小到6毫米时，深度剂量曲线的形状或绝对剂量（<2.5%）没有明显变化。测量表明，在浅深度（=0.7克/立方厘米），很大一部分剂量是由从机头部件散射的质子传递的。简单的准直可以减少这种影响。
IBA眼部质子系统的剂量学和定位特性足以在可接受的临床边界内治疗眼部病变。建议的改进措施包括限制输出对射程的依赖性并减少机头散射。
