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Introduction to Particle Therapy
The probability of developing cancer increases with age. Due to an aging society and increasing life expectancy, cancer therapy will become even more important than today.
Despite extensive research, today only one out of every two patients is successfully cured.
Particle therapy will especially benefit patients with radiation resistant tumors or tumors too close to critical organs to be treated by conventional radiation therapy or surgery.
Therefore, particle therapy is reported to be a very important advance in cancer therapy, especially for the 18% of patients where local therapy failed (see graphic below).
Why Particle Therapy?
The advantages of particle therapy in comparison to radiotherapy with photons are improved dose conformity to the planned target volume as well as the increased biological effectiveness to the tumor but not the normal tissue in the entrance channel. These advantages allow the successful treatment even of radiation resistant tumors.
Bragg Peak
The lower integral dose to the normal tissue outside the target volume is a consequence of the physical properties of particles compared to photons. In photon radiotherapy, the dose decreases exponentially with depth after an initial build-up effect, while for particles the highest dose is deposited at the end of the range in the so called Bragg peak. Using the intensity modulated particle delivery this high and
As a consequence of the high conformity, tumors in close vicinity to critical organs can be treated with high doses. Because of the decreased integral dose to the normal tissue, the probability of developing recurrences and secondary cancer in the tissue surrounding the tumor is significantly reduced. Several clinical studies by GSI, PSI, and MGH show that, for these reasons, proton therapy is especially suited for pediatric tumors.
biologically effective dose is concentrated in the target volume.
Carbon Ions in Particle Therapy
While the clinical use of protons is accepted today, radiobiologists and radiooncologists all over the world also see the potential of heavier ions. More than 5000 studies from Japan and Germany show good results with carbon ions.
The higher mass of carbon ions compared to protons reduces the depth and lateral scattering by more than a factor of 3 independent of penetration depth. Higher tumor dose and less impact on normal tissue even for deep-seated tumors combined with increased biological effectiveness can be achieved with carbon ions.
Treatment plan for protons applied using passive beam scattering technique (Courtesy of iThema Labs)
While protons are comparable to photons considering their radiobiological beam properties, carbon ions show a higher relative biological effectiveness (RBE). As a consequence of the higher biological effectiveness, otherwise radiation resistant tumors – such as slow-growing or hypoxic tumors - become sensitive to carbon treatment. Furthermore, the number of treatment fractions are expected to be considerably decreased, compared to standard conventional radiotherapy methods.
Treatment plan for carbon ions applied using active scanning technology (Courtesy of GSI, Darmstadt)
For about 50 years, this new approach in treating cancer has been studied at research institutes with very encouraging results. Worldwide approximately 75,000 patients have already been treated with particle therapy, Particle therapy is currently being used in over 25 centers worldwide. Intensity modulated particle therapy (IMPT) with heavier ions is technologically far more challenging because of the more dedicated particle accelerators and the more complex treatment planning and beam application. The most dedicated irradiation method, active beam scanning, scans the target with a pencil ion beam in three dimensions.
*Siemens Particle Therapy products and solutions are works-in-progress and require country specific regulatory approval prior to clinical use.
