Defining radiation targets
After the staging investigation, your attending physician will keep you informed about the spread of the tumor and any metastases. This will define the target or targets for proton radiation, which your physician will explain to you during the second consultation. If necessary, your physician will also draw on the expertise of the Tumor Board of Specialists, which has discussed your case in detail. In isolated cases, the immediate environment of the tumor--for example, the blood vessels--may need to undergo additional testing. The procedures carried out here include endoscopy, sonography (ultrasound) and angiography, either in NMI tomographs or in computer tomographs. All the equipment for these examinations is available at the RPTC.
Unlike x-ray radiation, proton radiation is extremely precise across all three spatial dimensions. The beams are so accurate that they can be targeted with deviations of less than 1 millimeter in critical areas of the body, such as the brain. Naturally, the radiation equipment must be precisely adjusted to the defined target area, and this process is relatively complex.
The most important precondition is that the patient must remain in precisely the same position for target definition and at the time when the radiation is administered. Accordingly, you will be immobilized beforehand, usually on a contour mattress. A contour mattress is made of an airtight plastic film filled with small polystyrene balls, which is then evacuated using a process similar to that used in vacuum packaging for foam peanuts. The balls conform to the contours of your body, and the vacuum holds you in a fixed position. Your body will also be fixed in the mattress using a suction film from which the air has also been removed. This bed is reserved for you personally throughout your treatment.
If your skull is being irradiated, an impression of the upper jaw will be taken. This allows your head to be precisely positioned so that only a few additional supports are necessary. If your eyes are being irradiated, targeting will involve significant technical resources. (see “Frequently Asked Questions").
In some cases, short-acting anesthesia is needed for diagnosis and radiation treatment performed --in children, for example, who generally find it difficult to keep still. Regarding tumors in the lungs and liver, the movements involved in breathing also play a significant role. When this is the case, the lung is placed in a controlled inflated state with oxygen during short-acting anesthesia, which enables precise tumor targeting. Hypoxia does not occur.
For more information, please download the PDF file entitled “Process Support With Anesthesia Procedures” here (in German only).
Computer tomography is always used for tumor targeting. It no longer scans the entire body but instead irradiates two-millimeter-thick layers with maximum precision. These images are stored and processed three-dimensionally as a data set. If an MRI scan is able to visualize the tumor better, the MRI images will be overlaid electronically on the CT images. If necessary, additional images from the PET scan will be displayed as well.
Immediately upon completion of diagnostics, physicians will define the target area and access channels for radiation. If the tumors are very small (eye or brain stem), very thin beams are used instead of three-dimensional scanning. Templates are used to match the beams to the tumor target area.
Once tumor targeting is complete, our medical physicists and radio-oncologists need another few days for therapy planning and preparation. Our patient management staff will inform you promptly as soon as therapy can begin and will coordinate the next steps with you.