In this thesis a tracking system was developed by modifying an add-on collimator the Siemens
Moduleaf for realtime applications in radiotherapy. As the add-on collimator works almost
completely autonomously of the linear accelerator (LinAc) no modifications to the latter were
necessary. The adaptations to the Moduleaf were mainly software-based. In order to reduce the
complexity of the system outdated electronic parts were replaced with newer components where
practical. Verification was performed by measuring the latency of the system as well as the
impact on applied dose to a predefined target volume moving in the leaf's travel direction.
Latency measurements in software were accomplished by comparing the target and current
positions of the leaves. For dose measurements a Gafchromic EBT2 film was placed beneath the
target 4D phantom in between solid water plates and moved alongside with it. Based on the
results a tracking-capable add-on collimator seems to be a useful tool for reducing the
margins for the treatment of small slow-moving targets. Radiotherapy is one of the most
important methods used for the treatment of cancer. Irradiating a moving target is also one of
the most challenging tasks to accomplish in modern radiotherapy.
