Heavy Ion Therapy: Status and Perspectives

Starting with the pioneering work at the University of California in Berkeley in 1977, heavy ion radiotherapy has been of increasing interest especially in Japan and Europe in the last decade. There are currently 3 facilities treating patients with carbon ions, two of them in Japan within a clinical setting. In Germany, a research therapy facility is in operation and the construction of a new hospital based facility at the Heidelberg university will be started soon. An outline of the current status of heavy ion radiotherapy is given with emphasis to the technical aspects of the respective facilities. This includes a description of passive and active beam shaping systems, as well as their implications for treatment planning and dosimetry. The clinical trials and routine treatments performed at the German heavy ion facility are summarized.

An overview over the upcoming new facilities and their technical possibilities is given. It is discussed what the necessary improvements are to fully exploit the potential of these facilities. Especially the new Heidelberg facility with the possibility of active beam scanning in combination with the first isocentric gantry for ions and offering beams of protons, helium, oxygen and carbon ions has implications on treatment planning, dosimetry and quality assurance. The necessary and ongoing developments in these areas are summarized. The new facilities also offer the possibilities to perform more extensive clinical studies and to explore future indications for radiotherapy with heavy ions. An overview over the indications and treatment schemes is also given.

Inverse planned stereotactic intensity modulated radiotherapy (IMRT) in the treatment of incompletely and completely resected adenoid cystic carcinomas of the head and neck: initial clinical results and toxicity of treatment

BACKGROUND

Presenting the initial clinical results in the treatment of complex shaped adenoid cystic carcinomas (ACC) of the head and neck region by inverse planned stereotactic IMRT.

MATERIALS

25 patients with huge ACC in different areas of the head and neck were treated. At the time of radiotherapy two patients already suffered from distant metastases. A complete resection of the tumor was possible in only 4 patients. The remaining patients were incompletely resected (R2: 20; R1: 1). 21 patients received an integrated boost IMRT (IBRT), which allow the use of different single doses for different target volumes in one fraction. All patients were treated after inverse treatment planning and stereotactic target point localization.

RESULTS

The mean follow-up was 22.8 months (91-1490 days). According to Kaplan Meier the three year overall survival rate was 72%. 4 patients died caused by a systemic progression of the disease. The three-year recurrence free survival was according to Kaplan Meier in this group of patients 38%. 3 patients developed an in-field recurrence and 3 patient showed a metastasis in an adjacent lymph node of the head and neck region. One patient with an in-field recurrence and a patient with the lymph node recurrence could be re-treated by radiotherapy. Both patients are now controlled. Acute side effects >Grade II did only appear so far in a small number of patients.

CONCLUSION

The inverse planned stereotactic IMRT is feasible in the treatment of ACC. By using IMRT, high control rates and low side effects could by achieved. Further evaluation concerning the long term follow-up is needed. Due to the technical advantage of IMRT this treatment modality should be used if a particle therapy is not available.

Treatment planning intercomparison for spinal chordomas using intensity-modulated photon radiation therapy (IMRT) and carbon ions

Spinal chordomas cannot be treated with an effective dose using conventional radiation therapy (RT) without exceeding the tolerance dose of the spinal cord while ensuring sufficient target coverage at the same time. In this study we investigate the potential physical advantages of combined photon intensity-modulated radiation therapy (IMRT) and raster-scanned carbon ion RT over photon IMRT alone. For a representative patient we generated a carbon ion RT plan and a photon IMRT plan. Additionally, combined plans consisting of both carbon ions and photon IMRT were calculated using ratios of 20:40 GyE, 30:30 GyE and 40:20 GyE. The best target coverage was obtained using carbon ions alone. Using a combination of photon IMRT and carbon ions, the target coverage was better than with photon IMRT alone. Due to the applied dose constraints, the sparing of the spinal cord was comparable for all plans. Using carbon ions alone, the non-target tissue volume irradiated to at least 30 GyE/50.4 GyE was reduced by 72%/84% compared to photon IMRT alone. These advantages were evident even with combined techniques. The actually delivered dose distribution is expected to be more dependent on patient misalignment with carbon ions compared with photon IMRT. A combination of carbon ions and photon IMRT might be preferable in order to profit by the physical advantages of carbon ions while ensuring a safe treatment.

Treatment planning for carbon ion radiotherapy in Germany: Review of clinical trials and treatment planning studies

The GSI carbon ion radiotherapy facility established the first completely active beam shaping system for heavy ions, using energy variation on the synchrotron and pencil beam scanning. The introduction of an active beam shaping system for carbon ions has considerable impact on the design of the treatment planning system (TPS). The TPS has to account for the capability of the beam delivery and the biological modelling, which is needed to calculate the RBE for the resulting varying depth dose modulation. The TPS used in clinical routine with carbon ions is described and its use in treatment planning studies are outlined. A clinical trial with carbon ion therapy as primary therapy for chordoma and chondrosarcoma of the base of skull has been completed in 2001. Currently, carbon ion therapy as a boost treatment together with conventional conformal photon therapy or IMRT is under investigation in clinical trials for adenoid cystic carcinoma, chordoma and chondrosarcoma of the cervical spine and sacrococcygeal chordoma. Treatment planning studies comparing carbon ion therapy with IMRT, using optimization of combination therapy, and optimization of beam-line design have already been completed. Analysis of uncertainties in treatment planning has been started with the investigation of range uncertainties stemming from CT imaging. Uncertainties coming from the beam delivery play only a minor role. An attempt to asses the uncertainties introduced in treatment plans by the biological modelling, was done, using phantom verification of calculated cell survival levels. The clinical trials and planning studies are of special importance for the upcoming new clinical ion facility of the Heidelberg university hospital.