De Conto C, Gschwind R, Martin E, Makovicka L
IRMA/LCPR-AC/CE, UMR 6249 CNRS, Université de Franche-Comté, BP 71427, 25211 Montbéliard, France; Centre Hospitalier Belfort Montbéliard, Service d'Oncologie et de Radiothérapie, site du Mittan, 56 boulevard du Maréchal Juin, 25209 Montbéliard, France.
IRMA/LCPR-AC/CE, UMR 6249 CNRS, Université de Franche-Comté, BP 71427, 25211 Montbéliard, France.
Phys Med. 2014 Feb;30(1):117-21. doi: 10.1016/j.ejmp.2013.03.002. Epub 2013 Apr 11.
Dental prostheses made of high density material contribute to modify dose distribution in head and neck cancer treatment. Our objective is to quantify dose perturbation due to high density inhomogeneity with experimental measurements and Monte Carlo simulations. Firstly, measurements were carried in a phantom representing a human jaw with thermoluminescent detectors (GR200A) and EBT2 Gafchromic films in the vicinity of three samples: a healthy tooth, a tooth with amalgam and a Ni-Cr crown, irradiated in clinical configuration. Secondly, Monte Carlo simulations (BEAMnrc code) were assessed in an identical configuration. Experimental measurements and simulation results confirm the two well-known phenomena: firstly the passage from a low density medium to a high density medium induces backscattered electrons causing a dose increase at the interface, and secondly, the passage from a high density medium to a low density medium creates a dose decrease near the interface. So, the results show a 1.4% and 23.8% backscatter dose rise and attenuation after sample of 26.7% and 10.9% respectively for tooth with amalgam and crown compared to the healthy tooth. Although a tooth with amalgam has a density of about 12-13, the changes generated are not significant. However, the results for crown (density of 8) are very significant and the discordance observed may be due to calculation point size difference 0.8 mm and 0.25 mm respectively for TLD and Monte Carlo. The use of Monte Carlo simulations and experimental measurements provides objective evidence to evaluate treatment planning system results with metal dental prostheses.
由高密度材料制成的牙科修复体有助于改变头颈癌治疗中的剂量分布。我们的目标是通过实验测量和蒙特卡罗模拟来量化高密度不均匀性引起的剂量扰动。首先，在一个代表人类颌骨的体模中进行测量，在三个样本附近放置热释光探测器（GR200A）和EBT2型变色薄膜：一颗健康牙齿、一颗有汞合金填充物的牙齿和一个镍铬合金牙冠，按照临床配置进行照射。其次，在相同配置下评估蒙特卡罗模拟（BEAMnrc代码）。实验测量和模拟结果证实了两个众所周知的现象：首先，从低密度介质过渡到高密度介质会引发背散射电子，导致界面处剂量增加；其次，从高密度介质过渡到低密度介质会在界面附近造成剂量降低。因此，结果显示，与健康牙齿相比，有汞合金填充物的牙齿和牙冠样本后的背散射剂量分别上升了1.4%和23.8%，衰减分别为26.7%和10.9%。尽管有汞合金填充物的牙齿密度约为12 - 13，但产生的变化并不显著。然而，牙冠（密度为8）的结果非常显著，观察到的不一致可能是由于热释光探测器和蒙特卡罗模拟的计算点尺寸分别为0.8毫米和0.25毫米。蒙特卡罗模拟和实验测量的使用为评估带有金属牙科修复体的治疗计划系统结果提供了客观证据。
