A novel breathing phantom was designed for being used in conventional and ion-beam radiotherapy as well as for medical imaging. Accurate dose delivery and patient safety are aimed to be verified for four-dimensional (4D) treatment techniques compensating for breathing-induced tumor motion. The phantom includes anthropomorphic components representing an average human thorax. It consists of real tissue equivalent materials to fulfill the requirements for dosimetric experiments and imaging purposes. The different parts of the torso (lungs, chest wall, and ribs) and the tumor can move independently. Simple regular movements, as well as more advanced patient-specific breathing cycles are feasible while a reproducible setup can be guaranteed. The phantom provides the flexibility to use different types of dosimetric devices and was designed in a way that it is robust, transportable and easy to handle. Tolerance levels and the reliability of the phantom setup were determined in combination with tests on motion accuracy and reproducibility by using infrared optical tracking technology. Different imaging was performed including positron emission tomography imaging, 4D computed tomography as well as real-time in-room imaging. The initial dosimetric benchmarking studies were performed in a photon beam where dose parameters are predictable and the dosimetric procedures well established.

EBT3 film dosimetry in an in-house developed phantom was successfully used to characterize the dosimetric properties of different (106)Ru plaque models. The film measurements were validated against MC calculations and other experimental methods and showed a good agreement with data from BEBIG well within published tolerances. The dosimetric information as well as interplaque comparison can be used for comprehensive quality assurance and for considerations in the treatment planning of ophthalmic brachytherapy.

4D dose calculation (4D-DC) is crucial for predicting the dosimetric outcome in the presence of intra-fractional organ motion. Time-resolved dosimetry can provide significant insights in 4D pencil beam scanning (PBS) dose accumulation and is therefore irreplaceable for benchmarking 4D-DC.In this study a novel approach of time-resolved dosimetry using five pinpoint ionization chambers (IC) embedded in an anthropomorphic dynamic phantom was employed and validated against beam delivery details. Beam intensity variations as well as beam delivery time-structure were well reflected with an accuracy comparable to the temporal resolution of the IC measurements.The 4D dosimetry approach was further applied for benchmarking 4D-DC implemented in the RayStation 6.99 treatment planning system. The agreement between computed values and measurements was investigated for: (i) partial doses based on individual breathing phases, and (ii) temporally distributed cumulative doses. For varied beam delivery and patient-related parameters the average unsigned dose difference for (i) was 0.04±0.03 Gy over all considered IC measurement values, while the prescribed physical dose was 2 Gy. By performing (ii), a strong effect of the dose gradient on measurement accuracy was observed. The gradient originated from scanned beam energy modulation and target motion transversal to the beam. Excluding measurements in the high gradient the relative dose difference between measurements and 4D dose calculations for a given treatment plan at the end of delivery was 3.5% on average and 6.6% at maximum over measurement points inside the target.Overall, the agreement between 4D dose measurements in the moving phantom and retrospective 4D-DC was found to be comparable to the static dose differences for all delivery scenarios. The presented 4D-DC has been proven to be suitable for simulating treatment deliveries with various beam-as well as patient-specific parameters and can therefore be employed for dosimetric validation of different motion mitigation techniques.

A pre-requisite prior clinical implementation of the treatment of moving targets with ion beams is the end-to-end evaluation of motion mitigation techniques such as gating, tracking, or rescanning. Utilizing anthropomorphic phantoms to mimic moving anatomy similar to organ and tumor motion of a patient is essential to assess both risks and benefits of the treatment and to test all steps involved in the treatment chain (