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Into the Future with Metrology - The Challenges of Medical Technology

Diagnostics and Therapy

Apply the right absorbed dose against the tumor

Calibration of dosimeters
Measurement setup for the calibration of dosimeters in units of absorbed dose to water at one of PTB's clinical linear accelerators.

Every year, half a million Germans are diagnosed with cancer – with an upward trend due to an ageing society. More than half of all cancer patients receive radiation therapy, either on its own or in combination with chemotherapy or surgery. Radiotherapy uses high-energy ionizing radiation to damage the genetic material of cancer cells, thus causing them to die. This can also affect healthy cells. In order to avoid such undesired side effects as far as possible and to maximize the healing success of radiation therapy, the energy deposited in the cells by the radiation must be close to an "optimum" value, and the spatial distribution of the radiation energy in the patient must match the shape of the tumor as closely as possible. Both can be achieved with the aid of modern methods of radiotherapy, such as intensity-modulated radiotherapy, radiotherapy with protons/ions or MR image-guided radiation therapy (MRgRT); the precise measurement of the energy deposited by the radiation plays a fundamental role here. This energy is characterized by the measurand of "absorbed dose" (unit Gray, Gy). With PTB’s primary standards, this unit can be realized with the worldwide lowest measurement uncertainty and disseminated via the calibration of secondary standards. Ultimately, all dosimeters used for this purpose in German radiation therapy hospitals are traceable to PTB’s primary standards via an uninterrupted calibration chain. In addition, modern methods of radiation therapy require the use of special procedures for dose measurement. In the case of MRgRT, for example, it is necessary to take the influence into account which the strong magnetic field that is required for imaging has on the dosimeter. In close cooperation with national and international partners such as other metrology institutes, research institutes and university hospitals, PTB is developing dose measurement procedures to be applied in modern radiation therapy and is making them available to the users (i.e. the medical physicists in the hospitals) in the form of national and international measurement regulations (standards and codes of practice).

 

Departments involved
Opens internal link in current window6.2 Dosimetry for Radiation Therapy and Diagnostic Radiology

Opens internal link in current window8.1 Biomedical Magnetic Resonance