Absorption wedge (radiation therapy)
An absorption wedge is a component in a linear accelerator in medicine. This is inserted under the multi-leaf collimator at the beam exit window . The design varies depending on the desired absorption effect. Usually the wedges are ground smooth and have an angular shape.
material
The material of the wedge is an internal company secret and varies depending on the manufacturer. Elements such as lead, iron and aluminum as well as copper can be included.
task
An absorption wedge should - as the name suggests - absorb radiation , ie "swallow" it. In radiation therapy, the healthy tissue should be spared as much as possible. To avoid overdosing, wedges are used to change the isodoses , as one side of the field is weakened more by radiation than the other. During planning, it is calculated and checked whether and which wedge is required. The type of wedge is also important. In more modern devices such as those made by the American manufacturer Varian , the planned wedge is “searched for” in the corresponding fields. If the wrong wedge or no wedge is used, or if the thick side of the wedge is on the wrong side, the computer will not allow the treatment to be released.
functionality
The indication of the angle sizes (e.g. 15 °, 30 ° or 60 °) do not relate to the actual wedge angle, but the change in isodose in 10 cm tissue depth. This dose curve is then changed by the corresponding angle. Measurements are made in the central beam , other angles at different material depths must be calculated.
Alternatives
Since the wedges are relatively imprecise and the radiology assistants have to enter the radiation room for the patient to B. turning a wedge is a rare sight today. Instead, use the field in field (FiF) technology. Instead of a wedge, a tuft of fields is planned there, which increases the dosage in part of the tissue to be irradiated. The "basic field" contains fewer MU (monitor units / monitor unit). The advantage is the considerable time savings and the lower radiation exposure for the staff (see main article: core photo effect and the resulting radiation protection problems in medicine )
Sources and individual references
- Theodor Laubenberger, J. Laubenberger: Technology of medical radiology . Diagnostics, radiation therapy, radiation protection. For doctors, medical students and MTRA. Deutsche Ärzte-Verlag, Cologne 1999, ISBN 3-7691-1132-X .