Institute of Medical Physics, University of Sydney, Australia.
Med Phys. 2010 Aug;37(8):4355-63. doi: 10.1118/1.3462558.
To compare and evaluate the dosimetric water equivalence of several commonly used solid phantoms for low energy photon beams.
A total of ten different solid phantom materials was used in the study. The PENELOPE Monte Carlo code was used to calculate depth doses and beam profiles in all the phantom materials as well as the dose to a small water voxel at the surface of the solid phantom. These doses were compared to the corresponding doses calculated in a water phantom. The primary photon beams used ranged in energy from 50 to 280 kVp.
A number of phantom materials had excellent agreement in dose compared to water for all the x-ray beam energies studied. RMI457 Solid Water, Virtual Water, PAGAT, A150, and Plastic Water DT all had depth doses that agreed with those in water to within 2%. For these same phantom materials, the dose changes in the water voxel at the surface of the solid phantom were within 2%, except for A150, which agreed to within 2.7%. By comparison, the largest differences in depth doses occurred for Plastic Water (-21.7%) and polystyrene (17.6%) for the 50 kVp energy photon beam and 8 cm diameter field size. Plastic Water gave the largest difference in the normalized beam profiles with differences of up to 3.5% as compared to water. Surface dose changes, due to the presence of the solid phantom acting as the backscatter material, were found to be up to 9.1% for polystyrene with significant differences also found for Plastic Water, PMMA, and RW3 phantoms.
The following solid phantoms can be considered water equivalent and are recommended for relative dosimetry of low energy photon beams: A150, PAGAT, Plastic Water DT, RMI457 Solid Water, and Virtual Water. However, the following solid phantoms give significant differences, compared to water, in depth doses, profiles, and/or in surface doses due to backscatter changes: Plastic Water, PMMA, polystyrene, PRESAGE, and RW3.
比较和评估几种常用固体体模在低能光子束中的剂量等效性。
本研究共使用了十种不同的固体体模材料。使用 PENELoPE 蒙特卡罗代码计算了所有体模材料中的深度剂量和射束轮廓，以及在固体体模表面的小水像素中的剂量。将这些剂量与在水模中计算的相应剂量进行了比较。使用的初级光子束能量范围为 50 至 280 kVp。
对于研究的所有 X 射线束能量，许多体模材料的剂量与水相比具有很好的一致性。RMI457 固体水、虚拟水、PAGAT、A150 和 Plastic Water DT 的深度剂量与水的差值均在 2%以内。对于这些相同的体模材料，在固体体模表面的水像素中的剂量变化在 2%以内，除了 A150 为 2.7%。相比之下，在 50 kVp 能量光子束和 8 cm 直径射野下， Plastic Water（-21.7%）和聚苯乙烯（17.6%）的深度剂量差异最大。Plastic Water 与水相比，归一化射束轮廓的差异最大，可达 3.5%。由于固体体模作为背散射材料的存在，表面剂量的变化高达 9.1%，聚苯乙烯的变化显著， Plastic Water、PMMA 和 RW3 体模也有显著差异。
以下固体体模可被认为是水等效的，并推荐用于低能光子束的相对剂量测量：A150、PAGAT、Plastic Water DT、RMI457 固体水和虚拟水。然而，以下固体体模在深度剂量、轮廓和/或表面剂量方面与水相比存在显著差异，这是由于背散射变化所致：Plastic Water、PMMA、聚苯乙烯、PRESAGE 和 RW3。
