Note
This topic is the continuation of our page: Radiotherapy
Synonyms
Irradiation planning, planning of radiotherapy, preparation of radiotherapy
Definition
Radiotherapy planning includes all preparatory measures necessary to perform radiotherapy according to the required quality criteria.
Procedure
The following steps are regularly carried out during irradiation planning:
- Storage
- Image acquisition
- Defining the therapy region
- Calculating the irradiation plan
- Simulation of the irradiation
- Transition to radiotherapy
Storage
The positioning of the patient must be selected in such a way that the patient lies comfortably and safely in a reproducible manner and that the treatment region can be reached as directly as possible by the therapy beam. Frequent examples are listed below:
- Positioning during irradiation of breast cancer (cancer of the female breast): In this case, the supine position with arms raised above the head or the inclined position to the healthy side has become accepted. In order to avoid wobbling, various positioning aids are used.
Arm holders, wedge pillows, vacuum mattresses. These measures ensure that the chest is easily accessible to the therapy beam and the lungs, heart and chest on the other side are largely spared.
- Positioning during irradiation of prostate cancer (cancer of the prostate gland of the man):The patient lies here on his back and a pillow is placed under the knees so that the pelvis can lie flat on the treatment table. A hollow back is thus avoided.
The arms lie on the chest.
- Positioning during irradiation in the head or ear, nose and throat area: Since the head is very mobile and at the same time critical regions are located in close proximity, the head must be fixed for radiotherapy to prevent damage to healthy organs (brain, eyes, nerves, etc.). Head masks made of thermoplastic material are most frequently used for this purpose. This special plastic material is heated and thus becomes elastic.
In this state it is pulled over the patient’s head and fixed to the treatment table. It adapts to the contours of the face similar to a plaster cast. The material cools down in a few minutes and further deformation is then no longer possible.
The mask is then put on before each radiation session.
Once the positioning is completed, a computed tomography (tomography of layers) of the therapy region is made in this position. With this image data a three-dimensional model of the patient is calculated. Furthermore, the first target markings are painted on the skin during computed tomography, which are required for the same positioning during irradiation.
There are three room lasers in the room of the computed tomograph and in the treatment room of the linear accelerator. One is mounted on the left, one on the right and the third above the treatment table. All three lasers meet in one point.
In the accelerator room, this is the point that is exactly one meter away from the point in the accelerator head where the X-ray beam is generated. At the same time, the rotation axis of the linear accelerator runs through this point, which it can circle 360°. In most cases, this point is localized in the tumor after completion of the treatment planning. If all three laser points correspond to the skin markings, the patient will lie exactly as he or she was lying during planning.
