Special radiation techniques in radiotherapy. Optimization, quality assurance and risk management

With the amendment of the Radiation Protection Ordinance of 2018, the issue of quality management has taken on an even more important role for the application of radiation therapy. In radiotherapy, a risk analysis must be carried out before the first use or a significant change in a treatment procedure. Two essential components of quality management are risk management and quality assurance. In the first part of the thesis, the aspect of risk management was digitized. A UML (Unified Modeling Language) activity diagram was used to model the clinical workflows. The subdivision of the workflows into different levels is done with the help of swim lanes, which can eventually be stored in a database. The second part of the thesis is dedicated to quality assurance. Since there are more and more components within the radiotherapy chain, a multimodal phantom was further developed, with which all steps (MR (magnetic resonance imaging), CT (computed tomography), treatment planning, irradiation incl. tracking), which the patient also goes through, are methodically checked. At each of these individual steps, a device-specific test is required before the next step is performed. In addition to these specific tests, such as the quantification of the distortion correction on the MRI, the transmission between the individual systems is also checked. Finally, in the so-called end-to-end test, a dosimetric check is performed using an ionization chamber in the phantom. The work is completed with the total skin irradiation technique. This was subjected to a risk analysis in connection with a significant change in an established treatment procedure. The basis was the adaptation of a traditional treatment technique for total skin irradiation ona new linear accelerator. The use of a special irradiation mode HDRE (High Dose Rate Electron) was introduced in a controlled manner, the technique was adapted to the geometry of the treatment room and the dose distribution was optimized dosimetrically and geometrically for homogeneity. Based on an existing risk analysis, various workflows were modeled in detail using UML.Part of the analysis were automatically generated risk matrices, which also included the risks of the medical devices used in a given workflow. Since the end-to-end test requires device-specific testing per device, additional suitable materials were necessary in the phantom, such as an MR plate consisting of silicone spheres. These allow quantification of the distortion correction. An additional gold marker in a silicone sphere enabled the phantom to be tracked on a motion sled. These features led to a positioning accuracy < 0.5 mm. For the adaption of the total skin technique, in order to ensure a homogeneous coverage at the required distance of 3.30 m, the horizontal gantry angles were calculated with an offset of 270°±19. The fixed mounting of the acrylic scatter plate and patient holder reduces the risk of misplacement compared to the mobile solution under the previously used methodology on the old linear accelerator. Since under the HDRE mode lower monitor values are required for the given dose, a relevant risk is seen in the use of too high monitor values from the old method, which would lead to an overdose. A structured guideline has been established, which is worked through step by step by MTAs and physicists, each of them additionally having to be checked by another person. In summary, a structured quality management in the areas of risk analysis and quality assurance was presented using two special techniques, rounded off with the digital risk management system. Furthermore, a so-called end-to-end test was performed on four stereotactic workflows based on the radiotherapeutic chain using a phantom developed in-house. In particular, the areas of MR and tracking at the linear accelerator were addressed, as there are still few all-encompassing phantoms in this area. This test serves both as a quality assurance of the individual devices and to check the communication of the individual systems.Total skin irradiation was successfully implemented and quality assured on a new linear accelerator. Furthermore, a risk analysis was performed comparing the new and old risks.