Vatnitsky S M, Miller D W, Moyers M F, Levy R P, Schulte R W, Slater J D, Slater J M
Department of Radiation Medicine, Loma Linda University Medical Center, CA 92354, USA.
Phys Med Biol. 1999 Nov;44(11):2789-801. doi: 10.1088/0031-9155/44/11/308.
Characterization of narrow beams used in proton stereotactic radiosurgery (PSRS) requires special efforts, since the use of finite size detectors can lead to distortion of the measured dose distributions. Central axis depth doses, lateral profiles and field size dependence factors are the most important beam characteristics to be determined prior to dosimetry calculations and beam modelling for PSRS. In this paper we report recommendations for practical dosimetry techniques which were developed from a comparison of beam characteristics determined with a variety of radiation detectors for 126 and 155 MeV narrow proton beams shaped with 2-30 mm circular brass collimators. These detectors included small-volume ionization chambers, a diamond detector, an Hi-p Si diode, TLD cubes, radiographic and radiochromic films. We found that both types of film are suitable for profile measurements in narrow beams. Good agreement between depth dose distributions measured with ionization chambers, diamond and diode detectors was demonstrated in beams with diameters of 20-30 mm. The diode detector can be used in smaller beams, down to 5 mm diameter. For beams with diameters less than 5 mm, reliable depth dose data may be obtained only with radiochromic film. The tested ionization chambers are appropriate for calibration of beams with diameters of 20-30 mm. TLD cubes and diamond detectors are useful to determine relative dose in beams with diameters of 10-20 mm. Field size factors for smaller beams should be obtained with diode and radiochromic film. We conclude that dosimetry characterization of proton beams down to several millimetres in diameter can be performed using the described procedures.
质子立体定向放射治疗（PSRS）中使用的窄束特性表征需要付出特殊努力，因为使用有限尺寸的探测器可能会导致测量的剂量分布失真。中心轴深度剂量、横向轮廓和射野大小依赖因子是在进行PSRS剂量学计算和束流建模之前需要确定的最重要的束流特性。在本文中，我们报告了实用剂量学技术的建议，这些建议是通过比较使用各种辐射探测器对126和155 MeV窄质子束进行测量得到的束流特性而制定的，这些质子束由2 - 30 mm圆形黄铜准直器塑形。这些探测器包括小体积电离室、金刚石探测器、高纯度硅二极管、热释光剂量计立方体、射线照相胶片和放射变色胶片。我们发现这两种胶片都适用于窄束中的轮廓测量。在直径为20 - 30 mm的束流中，电离室、金刚石探测器和二极管探测器测量的深度剂量分布之间显示出良好的一致性。二极管探测器可用于更小的束流，直径小至5 mm。对于直径小于5 mm的束流，只有使用放射变色胶片才能获得可靠的深度剂量数据。经过测试的电离室适用于直径为20 - 30 mm的束流校准。热释光剂量计立方体和金刚石探测器可用于确定直径为10 - 20 mm的束流中的相对剂量。较小束流的射野大小因子应使用二极管和放射变色胶片来获得。我们得出结论，使用所描述的程序可以对直径小至几毫米的质子束进行剂量学表征。
