Compensation body
A compensation body (or flatness filter ) is a component in a linear accelerator and is used in radiation therapy . This is an indispensable element in order to generate a homogeneous beam exit bundle. As a result, the tumor tissue to be irradiated is supplied uniformly and with known energy, there are no underdosing or overdosing.
The electrons of the irradiation device (e.g. particle accelerator ) striking a target material generate X-ray braking radiation and characteristic X-ray radiation , which are not homogeneously distributed.
With the help of a compensating body it can now be achieved that the dose distribution is approximately homogeneous. The structure of such an indispensable component is pointed in the middle and flattened on the edge. More photons are absorbed in the middle and fewer laterally. The radiation energy is hardened (soft parts are absorbed more strongly than hard parts) and the intensity is roughly the same everywhere. The compensation body is energy and device dependent. If you choose a different acceleration voltage, you have to change the compensating body via the device. This is usually done within the device using a turntable. In addition, more irradiation time is required per field, since the additional absorption by the compensating body reduces the dose rate.
It is also important that the dose maximum (located in the middle of the transverse profile ) hits the tip of the compensation body exactly. If this does not happen correctly, the 90 ° rotated monitor chambers in the accelerator head measure this and correct this automatically in the quadrupole lens in front of the deflection magnet . If a correction is not possible, the electron source switches off automatically. This prevents incorrect irradiation.
literature
- Hanno Krieger: Radiation sources for technology and medicine. 1st edition, Vieweg + Teubner, 2005, ISBN 978-3-8351-0019-0 .
- Rolf Sauer: Radiation Therapy and Oncology. 5th edition, Urban & Fischer, 2009, ISBN 978-3-437-47501-6 .