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Pictures of the Future
The Magazine for Research and Innovation

Medical Imaging

Individualizing Radiotherapy

Medical physicists use the images of a new computed tomography system to calculate the dose and duration of the radiation as well as the angle at which it will enter the patient’s body.

A new computed tomography system enables doctors to plan the radiation treatment of tumors with greater precision for each patient.

Siemens Healthineers is launching the world’s first computed tomography (CT) system that is specifically designed for radiotherapy. Known as the Somatom Confidence RT Pro, the system enables doctors to adapt tumor treatments to the needs of each patient. The new system focuses on the interface between radiologists and radiotherapy physicists, who jointly plan a patient’s treatment. Although both of these professions use the same CT images, the physicists require certain parameters that CT data previously lacked.

That’s because radiologists use default CT settings to prevent errors from occurring when this information is transferred by hand. However, for some patients, such as children or elderly and obese people, other settings would generate images that more clearly demarcate organs and tumors. In response, Siemens has developed an algorithm that calculates the data that is relevant for physicists for every CT image.

Thanks to this development, the Somatom Confidence RT Pro enables doctors to provide patients with personalized treatment that is also very secure against errors. Siemens decided to design a CT system that is designed specifically for radiotherapy, because the number of cancer patients and thus the frequency of radiation treatment is expected to grow as a result of demographic trends. The device has already been successfully tested by several customers.

Precise Therapy

There are three kinds of cancer treatment: chemotherapy, surgery, and radiotherapy. With radiotherapy, high-energy radiation – generally X-rays – is used to kill off tumor tissues. To create a treatment plan, an oncologist indicates the radiation’s target by marking a tumor’s outlines and organs that need to be spared during treatment in a 3D CT image set. Medical physicists then use these images to calculate the dose and duration of the radiation as well as the angle at which it will enter the patient’s body. Doctors must select an angle that enables the radiation to damage as little healthy tissue as possible as it passes through the patient’s body.

Precise radiotherapy mainly depends on the interaction between X-rays and the electrons in the tissues surrounding a tumor. The higher the electron density of the tissues, the more likely that radiation will cause damage. That’s why physicists use CT images to calculate tissue electron density in determining an optimum path for the radiation. To do this, they use a calibration curve, which describes the relationship between the electron density and the X-rays that were used to take the CT image. This calibration curve is created when the CT system is commissioned and then stored in the system’s radiation planning software.

Automation versus Individualization

The problem is that the calibration curve changes with the voltage applied to the CT scanner’s X-ray tube. This means that the CT images for planning the treatment have to be made with the same voltage as that used for the calibration curve – even if alternate voltages would enable doctors to more precisely demarcate tumors from their surrounding tissues which is the case for certain patients, such as children or elderly and obese people. However, this requires the use of a manual process for determining the electron density, because the required voltages aren’t stored in the CT data. Because this information would have to be passed on from the doctor to the physicist, mistakes could easily occur.

Automated Personalization

Thanks to the Somatom Confidence RT Pro, this process has now been automated.. This was accomplished by developing a direct density algorithm that calculates the electron density of every part of an image. As a result, CT images now also supply this value, which is directly transmitted to the radiotherapy physicist’s software. The algorithm calculates the electron density directly from the detector data and the settings of the X-ray tube instead of using a variety of saved calibration curves. As a result, the process is consequently far less prone to manual error and allows doctors to select any voltage and opens up many more opportunities for tailoring treatment to each person’s needs.

Christine Rüth
Picture credits: from top: 1. picture AJ_Watt/iStock by Getty Images