Forms of radiation therapy
Brain Tumor- Forms of radiation therapy, Total dose and fractionation, target volume and irradiation techniques are essentially determined by the spread characteristics of the respective tumor, the dose effect relationship of the tumor tissue, and the radiation tolerance of adjacent risk structures in the treatment of brain tumors. In addition to the radiation tolerance of the brain, the eye lenses, the optic chiasm and the optic nerve, as well as the brain stem and the cervical nerve, must be specially observed. According to the propagation characteristics of the individual tumors, three basic volume concepts are realized:
1. Local treatment (extended tumor region)
- Supratentorial tumors
- Low and high-grade gliomas,
- optic glioma
- Ependymom without CSF
- Man at examination
- Carry out the irradiation
2. Whole brain irradiation
- preventive treatment
- Malignant system diseases (lymphoblastic leukemias)
- brain metastases
- Radiation treatment of the whole head, including the cerebral membranes. Mask fixation to achieve precise radiotherapy.
3. Treatment of the entire cerebrospinal fluid space (neuro axis)
- Infratentorial tumors
- Supratentorial tumors with connection to the CSF system.
- Pinealistumoren (germ cell tumors, pinealoblastoma)
Irradiation of the tumor region
The treatment is concentrated on the tumor bed, including a safety margin with possible infestation (usually 2.0 cm) which is not detectable (with subclinical) by conventional imaging methods. To optimize the irradiation, individual computer-assisted irradiation plans are made in order to preserve as much surrounding tissue as possible (eg in low- and high-grade gliomas).
The application of individualized facial masks or post-bite techniques is a prerequisite for an exact positioning of the head. The area to be irradiated includes the tumor visible in CT or MRI, including areas with possible tumor infiltration. The advantages of computer-aided irradiation planning are the exact localization of the irradiation area as well as a precise delineation of critical organs such as the brain stem and the visual pathway (chiasma). Computer tomography also gains density values for physical irradiation planning, which are necessary for irradiation planning so that an individualized, optimal field adaptation and dose distribution can be calculated.
Stereotactic conformational therapy
Stereotactic conformational irradiations
Tumor-specific irradiation, ie individual adaptation to irregularly shaped tumors, is achieved by three-dimensional conformational irradiation. Special, individual collimators allow an individual field adjustment and thus the greatest possible protection of normal tissue.
Stereotactic single-time irradiation / Linear accelerator-assisted systems or Gamma Knife
The aim of the stereotactic one-time treatment is to apply a clinically sufficient dose within the tumor and to exclude or minimize the co-irradiation of normal, surrounding brain tissue.
It is possible to irradiate well-defined tumors of small extent with a single-time irradiation exactly and highly dosed. Stereotactic single-time irradiation typically occurs in individual brain metastases (not more than three), vascular malformations, and benign tumors that originate from the auditory nerve (acoustic neuroma). Linear accelerator-assisted systems and the Gamma Knife differ only in technical details, but not in the medical field of application. The essential technical difference between the two systems is as follows:
Gamma Knife: Over 200 individual telecobalt sources produce a radiation beam with the smallest diameter. The bundles intersect at one point. The bundling is achieved by a special helmet.
Linear Accelerator-Assisted Systems: The generated beam is defined by a special tube-shaped attachment on a small scale. This beam is guided over several arcs and concentrates at a defined point of intersection (isocenter). This achieves maximum focussing (as in a firing glass).
Whole brain irradiation (including the meninges, so-called “helmet field”)
The irradiation takes place via two lateral fields, which are 180 ° to each other. The target area comprises the brain structures in the case of metastases, but also in the case of leukemias but also the outer cerebral water spaces, which extend along the outer meninges of the brain. The latter areas often have to be integrated into the therapeutic area, since tumor cells (predominantly in the medulloblastoma, germ cell tumors and leukaemias) can be carried over the cerebrospinal fluid flow. An inadequate detection is therefore associated with an increased risk of a regression of the tumor disease, so that a particularly careful irradiation technique has a decisive effect on the treatment results. By means of special diaphragms, the remaining tissue of the head (eyes / face, mouth and throat) is discharged from the irradiation field.
Radiation treatment of the neuro axis
The brain and the spinal canal are irradiated with spinal sowings (medulloblastoma, germ cell tumors, lymphomas). It essentially consists of “helmet technology” (see above) and subsequent spinal irradiation fields. A reproducible bearing with appropriate fixing aids is the prerequisite for an exact field adjustment. Subsequently, as a rule, a local radiotherapy of the original tumor is performed. This irradiation technique usually corresponds to the above-mentioned procedure.