Monte Carlo (MC) simulations of beam interaction and transport in matter are increasingly considered as essential tools to support several aspects of radiation therapy. Despite the vast application ...of MC to photon therapy and scattered proton therapy, clinical experience in scanned ion beam therapy is still scarce. This is especially the case for ions heavier than protons, which pose additional issues like nuclear fragmentation and varying biological effectiveness. In this work, we present the evaluation of a dedicated framework which has been developed at the Heidelberg Ion Beam Therapy Center to provide automated FLUKA MC simulations of clinical patient treatments with scanned proton and carbon ion beams. Investigations on the number of transported primaries and the dimension of the geometry and scoring grids have been performed for a representative class of patient cases in order to provide recommendations on the simulation settings, showing that recommendations derived from the experience in proton therapy cannot be directly translated to the case of carbon ion beams. The MC results with the optimized settings have been compared to the calculations of the analytical treatment planning system (TPS), showing that regardless of the consistency of the two systems (in terms of beam model in water and range calculation in different materials) relevant differences can be found in dosimetric quantities and range, especially in the case of heterogeneous and deep seated treatment sites depending on the ion beam species and energies, homogeneity of the traversed tissue and size of the treated volume. The analysis of typical TPS speed-up approximations highlighted effects which deserve accurate treatment, in contrast to adequate beam model simplifications for scanned ion beam therapy. In terms of biological dose calculations, the investigation of the mixed field components in realistic anatomical situations confirmed the findings of previous groups so far reported only in homogenous water targets. This work can thus be useful to other centers commencing clinical experience in scanned ion beam therapy.
The dose conformation and the sparing of neighboring critical healthy structures are improved in carbon-ion beam radiotherapy in comparison to conventional photon radiotherapy. Inter and ...intrafractional plan adaptation strategies may preclude the quality assurance (QA) of the actually applied treatment plan before the treatment starts. Therefore, independent measurements of the positions of scanned pencil
C ion beams are of interest in order to monitor the beam application during the treatment and the beam in the isocenter. In this work, secondary ions outgoing from a patient-like phantom are exploited for the assessment of the lateral pencil beam position in a clinic-like
C treatment fraction. The experiment was performed at the Heidelberg Ion-Beam Therapy Center (HIT) in Germany. A carbon-ion treatment plan was used to treat a 100 cm
tumor volume in the center of an Alderson head phantom. Two silicon pixel detectors based on the Timepix3 technology developed at CERN were operated in synchronization to detect and to track outgoing secondary ions. We established an analysis of the measured secondary ion track distribution which enabled us to follow the beam scanning movement of the carbon-ion pencil beam by assessing the lateral position of the single beam spots. The precision of the developed method was found to range from 0.84 mm to 2.59 mm. For beam energies greater than 197.58 MeV/n, the mean of absolute distances of the measured lateral pencil beam positions with respect to the pencil beam positions measured by the beam application system (averaged over each energy layer) were smaller than 2 mm. We conclude that the presented method has shown capabilities of monitoring the lateral pencil beam positions by means of secondary ions with precision and sensitivity of clinical interest.
Commissioning of treatment planning systems (TPS) and beam delivery for scanned light ion beams is an important quality assurance task. This requires measurement of large sets of high quality ...dosimetric data in anthropomorphic phantoms to benchmark the TPS and dose delivery under realistic conditions.
A novel measurement setup is described, which allows for an efficient collection of a large set of accurate dose data in complex phantom geometries. This setup allows dose measurements based on a set of 24 small volume ionization chambers calibrated in dose to water and mounted in a holder, which can be freely positioned in a water phantom with various phantoms mounted in front of the water tank. The phantoms can be scanned in a CT and a CT-based treatment planning can be performed for a direct benchmark of the dose calculation algorithm in various situations.
The system has been used for acceptance testing in scanned light ion beam therapy at Heidelberg Ion Beam Therapy Center for scanned proton and carbon ion beams. It demonstrated to be useful to collect large amounts of high quality data for comparison with the TPS calculation using various phantom geometries.
The setup is an efficient tool for commissioning and verification of treatment planning systems. It is especially suited for dynamic beam delivery, as many data points can be obtained during a single plan delivery, but can be adapted also for other dynamic therapies, like rotational IMRT.
We describe a method to irradiate arbitrarily shaped target volumes with simultaneously optimized multiple fields of fast carbon ions, explicitly taking into account sparing of organs at risk. The ...method was developed with realistic technical boundary conditions in mind, so that irradiations can be executed with devices like the GSI raster scanner or its successors at the upcoming dedicated ion-beam radiotherapy facilities. By virtue of the local effect model (LEM) biological effects are fully taken into account. Several minimization algorithms were investigated, and plain gradient search was found to be more effective than methods based on conjugate gradients or Newton's root finding algorithm. Two sets of cell survival experiments for the experimental verification of patient-like treatment plans were performed. Chinese hamster cells were used for quasi two-dimensional biological dosimetry. The plans combine a very good target conformation with an excellent sparing of organs-at-risk which was verified by the measurements. The results are compared to predictions of the local effect model in its original formulation and a modified version taking additional effects of clustered DNA damage into account. The new method is implemented in GSI's TRiP98 treatment planning system. It has already been applied clinically for planning and irradiating selected patients within the GSI pilot project.
Purpose: Medical physics aspects of gated irradiation to moving tumors using scanned ion beams. Methods: At our institute, more than 700 patients have been treated with proton and carbon ion beams ...since its start. The first patient has now been treated with the application of gating. For this purpose, the Anzai respiratory motion detection and gating system was interfaced with the treatment control system such as to control spill pausing. The patient presented with a liver tumor moving with peak‐to‐peak amplitude of ∼1cm due to breathing. Treatment planning was performed using the Siemens Syngo RT‐Planning system on a 3DCT dataset. The gating window was determined from 4DCT. Plan verification was performed in a motion phantom, consisting of a PMMA block equipped with a 3D set of 24 pinpoint chambers mounted on the Quasar moving platform. The breathing motion perpendicular to the beam was simulated based on the trajectory obtained from the Anzai system during 4DCT acquisition. Dose was measured at three conditions: static phantom, moving phantom with continuous beam delivery, and moving phantom with gated irradiation. The statically delivered dose distribution was used as a reference. Further, a 4D dose calculation was performed on the 4DCT dataset using a research treatment planning system. Results: The relative rms deviations in the homogenous dose region were ∼18% without gating, and ∼6% with gating. The 4D dose calculation showed a decrease in target coverage by ∼20% and ∼6%, respectively, for the 95% isodose line. Conclusions: Gating of a scanned carbon ion beam was applied for treatment of a moving liver tumor and a workflow was developed to verify the dose to be actually delivered. With respect to continuous dose delivery, the target dose improvement achieved due to gating is considered to be significant for this patient.
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