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MEDICLINIC CITY HOSPITAL COMPREHENSIVE CANCER CENTRE

Radiotherapy Advantages
 
Since the late 1970s, radiotherapy has advanced mainly as a result of developments in computer technology. While the basic technology of the linear accelerator has remained the same, the planning options for treatment and the precision of irradiation have become more accurate. Thanks to the use of computer tomography, it is now possible to depict tumours within the body. The regions requiring radiotherapy can be marked on the CT layers, and the tumour can be recorded as a three-dimensional area.

Gentle Radiotherapy

The planning computer depicts thetumour as a three-dimensional volume, which then serves as the basis for the radiation plan created by the medical physicist. Mostly, the tumour volume will be “attacked” from various directions within defined safety margins, ensuring that the risk organs are omitted from the field arrangements, if possible. These fields are no longer rectangular, but are instead adapted using shielding in accordance with the defined radiation volume.The aim of any radio-oncological treatment is to subject the tumour region to the highest possible radiation dose while simultaneously protecting the risk organs to the greatest possible extent. The probability of being able to sterilise a tumour depends on its size and histology, as well as particularly on the radiation dose applied. However, the likelihood of suffering side effects depends on the exposure of normal, healthy tissue to radiation. In recent years it has become possible to control and modulate the intensity of the flow of photons within the field (intensity modulated radiotherapy, IMRT). As a result, the high-dose area can be better adapted to the defined tumour field and risk organs can be protected.

The more precise the treatment is, the less side effects are caused All these new technologies require the radiotherapy treatment to be carried out under exactly the same conditions. The geometry of the linear accelerator is fixed and the dose calculation is based on the assumption that the conditions are always exactly the same as those depicted in the planning computer tomography. If this deviates from the actual situation, the tumour region may be targeted with an insufficient dose, or a risk organ may be exposed to too much irradiation. If the position of the patient deviates by just one to two centimetres from the position originally planned, the radiation will also be “off-target” by this distance. This inaccuracy must be considered and included in the treatment concept. During planning, a safety margin around the tumour volume is calculated in order to ensure the most extensive radiation possible during all fractions. The disadvantage of this approach is a significant increase of the radiation volume, along with the corresponding side effects. The more precisely a radiation therapy can be performed, the smaller this required safety margin is and the smaller the treatment volume becomes.

On-board Imaging

In addition to the positioning aids described, it is now possible to check the accuracy of the patient’s position and particularly improve it with the help of a positioning control system. Two short radioscopies can be performed in different directions before the radiotherapy begins. These images show the current position of the patient and are then compared with a digital reconstruction of the planning CT. The images of the current radioscopy and the planning CT images are merged, so any deviations between the current radiation position and the originally planned position can directly be determined.
   

 

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