Gebauer Benjamin, Gantz Sebastian, Kunath Daniela, Hoffmann Aswin, Pawelke Jörg, Horst Felix
OncoRay - National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden and Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany.
Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiooncology - OncoRay, Dresden, Germany.
Med Phys. 2025 Jul;52(7):e17875. doi: 10.1002/mp.17875. Epub 2025 May 13.
The integration of MRI-guidance and proton therapy is a current research topic. Proton therapy with the patient being placed inside an in-beam MR scanner would require the presence of its static magnetic ( ) field to be taken into account in dose calculation and treatment planning. Therefore, dosimetric tools are needed to characterize dose distributions in presence of the field of the MR scanner. Furthermore, patient-specific quality assurance (QA) and treatment plan verification measurements should also be performed within the magnetic field.
In this work, the PTW Octavius 1500 ionization chamber array was characterized experimentally and tested for its suitability as a dosimetric tool for beam characterization and QA in MRI-guided proton therapy.
The dose rate response, response homogeneity and effective measurement depth of the detector were determined in experiments with scanned proton beams delivered by a horizontal beamline at OncoRay, Dresden. A patient-specific QA test including gamma analysis was performed for a realistic proton patient treatment plan at two different distances from the beam nozzle. In addition, experiments were performed in a in-beam MR scanner. These included measurements of square reference scanning patterns at different proton energies as well as measurements of a two-field patient treatment plan at different water equivalent depths.
The dose rate response was found to be linear up to . The effective measurement depth was determined to be . The response homogeneity was found to be suitable for the verification of proton treatment plans. The patient-specific QA test without magnetic field was satisfactory and also the measurements inside the in-beam MR scanner provided reasonable results. Their comparison allowed an assessment of the magnetic field effects on the dose distributions.
Concluding from these tests, the Octavius 1500 was found to be suitable for use as a dosimetric tool in MRI-guided proton therapy.
磁共振成像（MRI）引导与质子治疗的结合是当前的一个研究课题。将患者置于束流MRI扫描仪内进行质子治疗时，剂量计算和治疗计划需要考虑其静磁场（ ）。因此，需要剂量学工具来表征在MRI扫描仪磁场存在情况下的剂量分布。此外，还应在磁场内进行针对患者的质量保证（QA）和治疗计划验证测量。
在本研究中，对PTW Octavius 1500电离室阵列进行了实验表征，并测试其作为MRI引导质子治疗中束流表征和QA剂量学工具的适用性。
在德累斯顿OncoRay的水平束线输送扫描质子束的实验中，确定了探测器的剂量率响应、响应均匀性和有效测量深度。针对一个实际的质子患者治疗计划，在距束流喷嘴两个不同距离处进行了包括伽马分析在内的针对患者的QA测试。此外，还在束流MRI扫描仪中进行了实验。这些实验包括在不同质子能量下测量方形参考扫描模式，以及在不同水等效深度下测量两野患者治疗计划。
发现剂量率响应在高达 时呈线性。确定有效测量深度为 。发现响应均匀性适用于质子治疗计划的验证。无磁场情况下针对患者的QA测试结果令人满意，在束流MRI扫描仪内的测量也提供了合理结果。通过比较可以评估磁场对剂量分布的影响。
从这些测试得出结论，Octavius 1500适用于作为MRI引导质子治疗中的剂量学工具。
