Möckel D, Müller H, Pawelke J, Sommer M, Will E, Enghardt W
Forschungszentrum Dresden-Rossendorf, Institute of Radiation Physics, PF 510119, 01314 Dresden, Germany.
Phys Med Biol. 2007 May 7;52(9):2515-30. doi: 10.1088/0031-9155/52/9/012. Epub 2007 Apr 10.
Positron emission tomography (PET) as a method for quality assurance in radiotherapy is well investigated in the case of therapy with carbon ion beams and successfully applied at the Heavy Ion Medical Accelerator at Chiba (HIMAC), Japan, and the Gesellschaft für Schwerionenforschung (GSI), Germany. By measuring the beta(+) activity distribution during the irradiation (in-beam PET), valuable information on the precision of the dose deposition can be obtained. To extend this efficient technique to other radiation treatment modalities may be worthwhile. For example, since positron emitters are generated by high-energy photons with energies above 20 MeV due to (gamma, n) reactions (predominantly (11)C and (15)O in tissue), in-beam PET seems to be feasible for radiation therapy with high-energy photons as also shown in Geant4 simulations. Quantitative results on the activation of tissue-equivalent materials at hard photon beams were obtained by performing off-beam PET experiments. Homogeneous PMMA phantoms as well as inhomogeneous phantoms were irradiated with high-energy bremsstrahlung. After the irradiation the distributions of the generated positron emitters in the phantoms were measured using a conventional PET scanner. Furthermore, the depth-dose distributions were determined by means of optically stimulated luminescence detectors. In the experiments an activity per dose comparable to that produced in a typical patient irradiation with carbon ions could be achieved for 34 MV bremsstrahlung. In addition, a high contrast in the PET images for materials with different density and stoichiometry could be detected. Thus, further research concerning the development of in-beam PET seems to be worthwhile.
正电子发射断层扫描（PET）作为放射治疗质量保证的一种方法，在碳离子束治疗的情况下已得到充分研究，并成功应用于日本千叶的重离子医学加速器（HIMAC）和德国的重离子研究中心（GSI）。通过测量照射期间的β(+)活度分布（束内PET），可以获得有关剂量沉积精度的有价值信息。将这种有效技术扩展到其他放射治疗方式可能是值得的。例如，由于（γ，n）反应（组织中主要是(11)C和(15)O），能量高于20 MeV的高能光子会产生正电子发射体，束内PET似乎对于高能光子放射治疗也是可行的，正如在Geant4模拟中所示。通过进行束外PET实验，获得了硬光子束作用下组织等效材料活化的定量结果。用高能轫致辐射照射均匀的聚甲基丙烯酸甲酯模体以及非均匀模体。照射后，使用传统的PET扫描仪测量模体内产生的正电子发射体的分布。此外，通过光激发发光探测器确定深度剂量分布。在实验中，对于34 MV的轫致辐射，可以实现与典型碳离子患者照射中产生的每剂量活度相当的活度。此外，在PET图像中可以检测到不同密度和化学计量比材料之间的高对比度。因此，关于束内PET发展的进一步研究似乎是值得的。
