Hadrontherapy treatment requires diagnostic MRI, CT and PET images to be acquired at the Centre.
In addition to the lesion, these scans detect several point-like markers placed on an immobilization system applied on the patient, which will later be used during irradiation.
The images are processed by complex software to:
- generate a three-dimensional treatment plan of the tumor which is optimized to the patient
- contain all the information on the position and geometry of the tumor with respect to the markers
The typical elements of a treatment plan include the angle of the irradiation fields, which takes into account changes in the patient positions with respect to the fixed particle beam.
The hadrontherapy session begins with a precise positioning of the patient “immobilized” as in the diagnostic images on a special flat-couch with markers (slab of carbon fiber), and placed on a manual trolley. This positioning is done in the preparation room called CAP (Computer Aided Positioning) near to the treatment room. In the CAP, the positions of all markers are determined with high precision using suitable detection systems.
Together with the diagnostic images described above, these systems determine the location of the tumor and all of its geometrical parameters (shape, size, orientation) on the carbon fiber couch on which the patient lies. This process can take several minutes.
Subsequently, the patient and the carbon fiber couch are coupled to a robotic arm in the treatment room. The robotic arm, connected to the computer system, places the patient on the beam line in a position dependent on the treatment plan and information markers. The position is controlled by the continuous detection of the markers (using infra-red cameras and emitters) and X-ray images. In this way, the control of the positioning of the target (tumor) on the beam is obtained with high accuracy (1st field).
Once the correct position is located and verified, the irradiation begins: a narrow pencil beam of protons scans the tumor sequentially destroying section after section. The pencil beam “brushes” (destroying) a section of the tumor following commands as determined by the treatment plan, based on the shape of the particular section. The transition to the next deeper section is obtained by increasing the beam energy, and so on for all the sections into which the tumor has been divided by the treatment plan. If the treatment plan indicates other fields, the patient will be moved to the new treatment position by the robotic couch, following controls (markers and X-ray images) prior to new irradiation. The same approach is used for any subsequent fields.
The entire radiation lasts from 100 to 200 seconds, while the transition between different fields requires about 5-10 minutes for controls (mainly determined by the slow movement of the robotic couch).
With the patient always immobilized on the couch robot, further irradiation (boost) with carbon ions in each field may be carried out if required by the treatment plan.
The whole process is constantly monitored (every twenty milliseconds), so that any detection of abnormality results in an immediate termination of the irradiation.
Treatment continues for a number of subsequent sessions determined by the initial treatment plan and the subsequent diagnostic images. Given the high efficacy of the carbon ion therapy, 3 to a maximum of 5 sessions may be required.
When the radiation is completed, the carbon fiber couch with the patient is returned to the trolley and transferred to an adjacent room for discharge from the centre.