Nauraye C, Mazal A, Delacroix S, Bridier A, Chavaudra J, Rosenwald J C
Centre de Protonthérapie d'Orsay, France.
Int J Radiat Oncol Biol Phys. 1995 Jul 15;32(4):1177-83. doi: 10.1016/0360-3016(95)00006-k.
The development of a scattering system for a proton therapy beam line dedicated to ophthalmological applications.
A protontherapy beam line has been developed for the treatment of uveal melanoma at the Orsay synchrocyclotron. The original 200 MeV proton beam is degraded to 76 MeV and the final beam characteristics (range, modulation, flatness, collimation) are obtained with beam modifiers in the treatment room. A passive scattering system is used to obtain a uniform dose distribution in the beam cross-section throughout 30 mm in diameter, with minimal losses in energy and dose rate. We have used an experimental approach for the scattering study.
An elliptical ring shaped from 0.1-mm thick lead is the solution we have adopted for the scattering system. For a modulated beam, a flatness of 1% is obtained on transverse profiles. The energy loss introduced by this scatterer is only 0.5 MeV, with no appreciable change in the range over the treatment field. For an unmodulated beam, 21% of intensity is lost when the scatterer is used. The distal and the lateral dose fall-off (90-10%) for a modulated beam are 2.6 mm. These last values are independent of the range and the modulation currently used for the ophthalmic applications.
A specific passive scattering system can be adapted to a particular beam emittance. A systematic experimental approach can easily be undertaken to obtain the scatterer adapted for small irradiation fields in proton therapy.
开发一种用于眼科应用的质子治疗束流线路的散射系统。
在奥赛同步回旋加速器上开发了一条用于治疗葡萄膜黑色素瘤的质子治疗束流线路。原始的200兆电子伏特质子束被衰减至76兆电子伏特，最终的束流特性（射程、调制、平坦度、准直）通过治疗室内的束流修正器获得。使用被动散射系统在直径30毫米的整个束流横截面上获得均匀的剂量分布，同时能量和剂量率损失最小。我们采用了实验方法进行散射研究。
我们采用了由0.1毫米厚的铅制成的椭圆形环作为散射系统的解决方案。对于调制束，横向剖面的平坦度为1%。该散射体引入的能量损失仅为0.5兆电子伏特，在治疗野内射程没有明显变化。对于未调制束，使用散射体时强度损失21%。调制束的远端和侧向剂量下降（90 - 10%）为2.6毫米。这些最终值与目前眼科应用中使用的射程和调制无关。
特定的被动散射系统可适应特定的束流发射度。可以轻松地采用系统的实验方法来获得适用于质子治疗中小照射野的散射体。
