Interview with Dr. Christian Pychlau
Why is the calibration of dosimeters so important?
If radiation measuring equipment is not recalibrated regularly, the user runs the risk that it will not function as designed. Small but significant deviations within the measurements can thus remain undetected. The detectors and instruments are very stable and can generally be used for a long time, if handled professionally. We recommend recalibration for our own equipment once every two years. If a detector is defective to the extent that there are large deviations, this becomes immediately apparent to the user. However, small deviations of e.g. below five percent may go unnoticed in the daily hustle and bustle in the clinic. Regular calibrations allow errors to be discovered and corrected in time. Hence the call from us to all users: Take the calibrations seriously! If a detector behaves differently than it normally does, investigate it further in order to protect your patients.
Worst case scenario: What can happen if calibrations are not carried out regularly?
A detector can look intact from the outside but can still be defective. Detectors are generally very stable, but if an ionization chamber falls on the floor just once, or even if it is put down too hard on the table, it can be damaged. In the 1990s a colleague of mine visited a number of rural hospitals in Asia. In many cases there were no doctors or physicists present, and staff had very little knowledge about medical physics. Thus, the dosimetry and quality assurance measurements were carried out – if at all – at a low level. He witnessed many deficiencies – from non-functional X-ray tubes to defective beam-scanning mechanisms, all of which could have been detected by appropriate quality assurance measures and calibrated equipment.
How can users assess the quality of a calibration?
A pre-requisite is the successful accreditation of the calibration laboratory to the current standards and then consistently positive audit results. One indication of high quality are the high level of qualifications and many years of experience of the laboratory staff. The PTW Secondary Standard Calibration Laboratory has been around since the 1920s. Every year we carry out more than 12,000 calibrations on hundreds of different dosimeters and appliances, including those of other manufacturers. Comparison measurements with PTB or IAEA are always within the pro-Mille range, therefore well below the combined uncertainty. These facts demonstrate the high quality of our calibrations.
Read the full article in EFOMP’s EMP Summer News, page 70 – 71.