What is Dosimetry and Why is it Important for Cancer Treatment?

Whether weighing out apples at the supermarket or medication at the drug store, accurate measurements are important in everyday life. The decisions we make depend on the amount we buy--or rather the measured weight--of the product. While an error of a few percent may not be of grave concern when buying fruits and vegetables, when it comes to medical treatment for disease it is certainly necessary to be precise. But, what if the thing we are measuring is completely invisible? Ionizing radiation, which can be used to treat cancer by destroying harmful cells but is completely undetectable by human senses, requires the utmost care in ensuring it is accurately measured. Otherwise, too little or too much radiation can be harmful to the cancer patient that is being treated.

How do we measure medical radiation?

During treatment, cancer patients are given very specific and targeted amounts of radiation in order to destroy cancer cells.

To measure the doses, an instrument is placed in a radiation beam, which produces an electrical charge inside the instrument. Depending on the size of the electric charge or current, scientists can determine the corresponding amount of deposited energy the instrument received. The next step is to ’convert’ the electrical quantity into a radiation dose by applying a calibration coefficient, a number that signifies an amount of radiation based on the corresponding electrical quantity.

Yet, the measurement of the electrical quantity can differ depending on the type of radiation beam (photons, electrons, etc.), the material the instrument is made out of, or the environmental conditions at the time of the experiment.

How do we make sure the right “amount” of radiation is delivered to cancer patients?

Because the determination of an absorbed dose is complex and depends on many external and internal factors, the dosimetry community—which includes the International Atomic Energy Agency, the Bureau International Des Poids et Mesures (BIPM), the International Commission of Radiation Units and Measurements (ICRU), as well as several medical physics professional societies—decided in the late sixties to standardize the procedures by creating ‘dosimetry protocols” or “codes of practices” These include details on the types of instruments to be used, measurement conditions and calculation procedures.

The idea is that by encouraging countries to use a unique dosimetry protocol, together with an instrument whose calibration is traceable to national standards, dosimetry—or the determination of radiation doses—will be highly consistent. Consistency in dosimetry at the national level is critical for quality radiotherapy treatment and supports sound clinical trial studies for comparing various types of treatment modalities.

The IAEA dosimetry laboratory is dedicated to helping the capacity building of Member States in dosimetry. By developing and maintaining measurement standards, providing dosimetry calibration services, postal dose audits and training and education opportunities, cancer patients around the world are better able to receive safe and effective treatment.

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