Tumour targeting
Second consultation
Subsequent to the staging investigation, your attending physician will keep you informed about the spread of the tumour and any metastases. This will define the target or targets for the proton radiation, which are to be explained by your physician during the second consultation. In reaching this decision, your physician will also draw on the Tumour Board of Specialists, which has discussed your case in detail. In isolated cases, the immediate environment of the tumour--for example, the blood vessels--may become subject to further investigations. 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.
Immobilization
Contrary to the situation in x-ray radiation, proton radiation operates with extreme precision in all three spatial dimensions. The beams are so accurate that they can be targeted with deviations of less than 1 millimetre 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 the target definition and later, when the radiation is administered. Accordingly, you will be immobilized beforehand, generally using a contour mattress. This 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 radiation is being carried out in the region of the skull, an impression of the upper jaw will be taken by a dentist. 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 under "Answers to Frequently Asked Questions").
Short-acting anaesthesia
In some cases, diagnosis and radiation are carried out under short-acting anaesthesia--in children, for example, who generally find it difficult to keep still. Regarding tumours 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 anaesthesia, which allows the tumour to be targeted precisely. No shortage of oxygen results.
Computertomography
Tumour targeting is always carried out using computer tomography. It no longer scans the entire body but instead irradiates two-millimetre-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 tumour better, then the MRI images will be overlaid electronically on the CT images. If necessary, further images from the PET scan will be displayed as well.
Immediately upon the completion of the diagnostic phase, the physicians will define the target area and the access channels for radiation. If the tumours are very small, for example in the eye or the brain stem, very thin beams are used instead of three-dimensional scanning. The beams are matched to the tumour target area through the use of templates.
Once this preliminary work is finished, everything is ready for you to be incorporated in the schedule for radiotherapy.