Oliver Jäkel

Treatment planning for heavy-ion radiotherapy: physical beam model and dose optimization

We describe a novel code system, TRiP, dedicated to the planning of radiotherapy with energetic ions, in particular 12C. The software is designed to cooperate with three-dimensional active dose shaping devices like the GSI raster scan system. This unique beam delivery system allows us to select any combination from a list of 253 individual beam energies, 7 different beam spot sizes and 15 intensity levels. The software includes a beam model adapted to and verified for carbon ions. Inverse planning techniques are implemented in order to obtain a uniform target dose distribution from clinical input data, i.e. CT images and patient contours. This implies the automatic generation of intensity modulated fields of heavy ions with as many as 40000 raster points, where each point corresponds to a specific beam position, energy and particle fluence. This set of data is directly passed to the beam delivery and control system. The treatment planning code has been in clinical use since the start of the GSI pilot project in December 1997. Forty-eight patients have been successfully planned and treated.

Carbon ion radiotherapy in Japan: an assessment of 20 years of clinical experience

Charged particle therapy is generally regarded as cutting-edge technology in oncology. Many proton therapy centres are active in the USA, Europe, and Asia, but only a few centres use heavy ions, even though these ions are much more effective than x-rays owing to the special radiobiological properties of densely ionising radiation. The National Institute of Radiological Sciences (NIRS) Chiba, Japan, has been treating cancer with high-energy carbon ions since 1994. So far, more than 8000 patients have had this treatment at NIRS, and the centre thus has by far the greatest experience in carbon ion treatment worldwide. A panel of radiation oncologists, radiobiologists, and medical physicists from the USA and Europe recently completed peer review of the carbon ion therapy at NIRS. The review panel had access to the latest developments in treatment planning and beam delivery and to all updated clinical data produced at NIRS. A detailed comparison with the most advanced results obtained with x-rays or protons in Europe and the USA was then possible. In addition to those tumours for which carbon ions are known to produce excellent results, such as bone and soft-tissue sarcoma of the skull base, head and neck, and pelvis, promising data were obtained for other tumours, such as locally recurrent rectal cancer and pancreatic cancer. The most serious impediment to the worldwide spread of heavy ion therapy centres is the high initial capital cost. The 20 years of clinical experience at NIRS can help guide strategic decisions on the design and construction of new heavy ion therapy centres.

Treatment planning for heavy ion radiotherapy: clinical implementation and application.

The clinical implementation and application of a novel treatment planning system (TPS) for scanned ion beams is described, which is in clinical use for carbon ion treatments at the German heavy ion facility (GSI). All treatment plans are evaluated on the basis of biologically effective dose distributions. For therapy control, in-beam positron emission tomography (PET) and an online monitoring system for the beam intensity and position are used. The absence of a gantry restricts the treatment plans to horizontal beams. Most of the treatment plans consist of two nearly opposing lateral fields or sometimes orthogonal fields. In only a very few cases a single beam was used. For patients with very complex target volumes lateral and even distal field patching techniques were applied. Additional improvements can be achieved when the patients head is fixed in a tilted position, in order to achieve sparing of the organs at risk. In order to test the stability of dose distributions in the case of patient misalignments we routinely simulate the effects of misalignments for patients with critical structures next to the target volume. The uncertainties in the range calculation are taken into account by a margin around the target volume of typically 2-3 mm, which can, however, be extended if the simulation demonstrates larger deviations. The novel TPS developed for scanned ion beams was introduced into clinical routine in December 1997 and was used for the treatment planning of 63 patients with head and neck tumours until July 2000. Planning strategies and methods were developed for this tumour location that facilitate the treatment of a larger number of patients with the scanned heavy ion beam in a clinical setting. Further developments aim towards a simultaneous optimization of the treatment field intensities and more effective procedures for the patient set-up. The results demonstrate that ion beams can be integrated into a clinical environment for treatment planning and delivery.

Therapy strategies for locally advanced adenoid cystic carcinomas using modern radiation therapy techniques

The authors evaluated whether modern photon techniques, such as stereotactic fractionated radiation therapy (FSRT) or intensity‐modulated RT, outweighed the biologic advantages of high‐linear‐energy transfer RT in the treatment of patients with locally advanced adenoid cystic carcinomas (ACC) that infiltrated the skull base or the orbit.

Treatment planning for scanned ion beams

Since 1997 a radiotherapy unit using fast carbon ions is operational at GSI. An intensity-controlled magnetic raster scanner together with a synchrotron allowing fast energy variation enable a unique method of purely active dose shaping in three dimensions. This contribution describes the necessary steps to establish a treatment planning system for this novel modality. We discuss the requirements for the physical beam model and the radiobiological model. Based on these we chose to implement a home-grown pencil beam model to describe the ion-tissue interaction and the Local Effect Model to calculate the RBE voxel-by-voxel. Given the large number of degrees of freedom biological dose optimization must be achieved by means of inverse treatment planning. All ion-related aspects are collected in our TRiP98 software. Biological dosimetry measuring cell survival in two dimensions turns out to be a good way to verify the model predictions as well as the actual irradiation procedure. We show a patient example and outline the future steps towards a dedicated clinic facility for all light ions.

Analysis of uncertainties in Gafchromic® EBT film dosimetry of photon beams

Radiotherapy today employs complex techniques in order to achieve the best possible conformity of the delivered dose to the target volume. When using dynamic dose delivery techniques, it is especially important to verify the delivered dose at as many representative points as possible. As a continuous medium, Gafchromic EBT film offers an excellent spatial resolution which, together with improvements in sensitivity as compared to older types of radiochromic films, make it a promising candidate for this purpose. In this paper we investigated whether EBT films can be used for quantitative dosimetry in photon beams. There are many publications which discuss different aspects of the EBT film dosimetry. Unfortunately, they differ in the used protocols, scanning devices and variables used for the film darkening quantification which makes the sources of uncertainties difficult to compare. Therefore, the overall accuracy and reproducibility of the results which can be reached with Gafchromic EBT films in combination with a commercial flatbed scanner was investigated. Both the film properties and the influence of the readout system were analysed and compared. The total uncertainty in the net optical density determination due to the studied effects was estimated to be 1.6% at 0.3 Gy and 0.8% at 1 Gy for 60Co photons. Based on this analysis of uncertainties, the handling and scanning protocol was optimized and methods to reduce the influence of some of the uncertainties were proposed. Although Gafchromic EBT films have significant advantages, there are certain effects which have to be considered in order to achieve 5% accuracy in the dose delivered to a patient.

Radiotherapy for chordomas and low-grade chondrosarcomas of the skull base with carbon ions

PURPOSE Compared to photon irradiation, carbon ions provide physical and biologic advantages that may be exploited in chordomas and chondrosarcomas. METHODS AND MATERIALS Between August 1998 and December 2000, 37 patients with chordomas (n = 24) and chondrosarcomas (n = 13) were treated with carbon ion radiotherapy within a Phase I/II trial. Tumor conformal application of carbon ion beams was realized by intensity-controlled raster scanning with pulse-to-pulse energy variation. Three-dimensional treatment planning included biologic plan optimization. The median tumor dose was 60 GyE (GyE = Gy x relative biologic effectiveness). RESULTS The mean follow-up was 13 months. The local control rate after 1 and 2 years was 96% and 90%, respectively. We observed 2 recurrences outside the gross tumor volume in patients with chordomas. Progression-free survival was 100% for chondrosarcomas and 83% for chordomas at 2 years. Partial remission after carbon ion radiotherapy was observed in 6 patients. Treatment toxicity was mild. CONCLUSION These are the first data demonstrating the clinical feasibility, safety, and effectiveness of scanning beam delivery of ion beams in patients with skull base tumors. The preliminary results in patients with skull base chordomas and low-grade chondrosarcomas are encouraging, although the follow-up was too short to draw definite conclusions concerning outcome. In the absence of major toxicity, dose escalation might be considered.

The heidelberg ion therapy center

The ion beam therapy facility presently under construction at the Department of Clinical Radiology, University of Heidelberg, Germany, will be the first dedicated and hospital-based irradiation facility for protons and heavier ions in Europe. A capacity of more than 1000 patient treatments per year is planned. The facility comprises two horizontally-fixed beamlines for patient treatments plus a fixed-beam experimental area. In addition, the world-wide first scanning ion gantry is under construction. The facility fully relies on an active beam delivery method, the intensity-controlled rasterscan technique. The availability of different ion species ranging from protons to oxygen under identical conditions optimally supports clinical trials aiming to clarify the question of which particle species is best suited for the individual indications. A linac-synchrotron combination will deliver libraries of energy-, focus- and intensity-variable pencil-beams for each ion species to the dose-delivering scanning systems at each treatment station. The available energies correspond to water-equivalent ranges from 2 cm to 30 cm. The intensity-controlled rasterscan technique allows for the administration of inversely planned and biologically optimized dose distributions having utmost precision. The facility will be equipped with state-of-the-art imaging modalities as well as an in-situ Positron-Emission-Tomography (PET). The commissioning of the different sections is scheduled for 2006. The pre-clinical operation will start early in 2007 followed by the routine patient treatment.

Three-dimensional accuracy and interfractional reproducibility of patient fixation and positioning using a stereotactic head mask system.

PURPOSE Conformal radiotherapy in the head and neck region requires precise and reproducible patient setup. The definition of safety margins around the clinical target volume has to take into account uncertainties of fixation and positioning. Data are presented to quantify the involved uncertainties for the system used. METHODS AND MATERIALS Interfractional reproducibility of fixation and positioning of a target point in the brain was evaluated by biplanar films. 118 film pairs obtained at 52 fractions in 4 patients were analyzed. The setup was verified at the actual treatment table position by diagnostic X-ray units aligned to the isocenter and by a stereotactic X-ray localization technique. The stereotactic coordinates of the treated isocenter, of fiducials on the mask, and of implanted internal markers within the patient were measured to determine systematic and random errors. The data are corrected for uncertainty of the localization method. RESULTS Displacements in target point positioning were 0.35 +/- 0.41 mm, 1.22 +/- 0.25 mm, and -0.74 +/- 0.32 mm in the x, y, and z direction, respectively. The reproducibility of the fixation of the patients head within the mask was 0.48 mm (x), 0.67 mm (y), and 0.72 mm (z). Rotational uncertainties around an axis parallel to the x, y, and z axis were 0.72 degrees, 0.43 degrees, and 0.70 degrees, respectively. A simulation, based on the acquired data, yields a typical radial overall uncertainty for positioning and fixation of 1.80 +/- 0.60 mm. CONCLUSIONS The applied setup technique showed to be highly reproducible. The data suggest that for the applied technique, a safety margin between clinical and planning target volume of 1-2 mm along one axis is sufficient for a target at the base of skull.

Relation between carbon ion ranges and x-ray CT numbers.

Measurements of carbon ion ranges in various phantom materials and real bones are presented. Together with measured Hounsfield values, an empirical relation between ranges and Hounsfield units is derived, which is an important prerequisite for treatment planning in carbon ion therapy.