X-ray leakage and scatter measurements

For 40 years, RTI has produced solutions for quality control and quality assurance for X-ray

RTI was the first company that produced a non-invasive kV meter for X-ray. Today, our multimeters measure all interesting parameters – in one exposure – in the primary beam, to make sure that the right output comes out from the X-ray system. However, not only measurements in the primary beam should be performed. Leakage radiation from the X-ray tube and scattered radiation in the X-ray room are parameters that should be tested to minimize the risk of unnecessary exposure of patients and staff at hospitals.

Leakage

An X-ray tube should be well shielded, but some X-ray can still leak out from it. Measurements must be performed to make sure the leakage levels are low and that no malfunctions, like cracks in the shielding, have occurred. The IEC standard 60601-1-3 states that the leakage out of the tube should be less than 1 mGy in one hour and at a distance of one meter from the focus point. This must be measured using a detector with an active area of 100 cm2, and it should be measured all around the X-ray tube with the collimation completely closed.

The IEC standard also states that no leakage should come out of the tube when no exposure is performed, like during warm-up of the cathode, etc. This test should be performed 5 cm from the tube surface, be less than 20 μGy in one hour, and measured using a detector with an active area of 10 cm². The set parameters during the tests depend on the X-ray unit, how much it is used in an average hour, what typical clinical parameters are, and local regulations in countries.

Scatter

When the primary X-ray beam hits a patient or a phantom, some of the beams will collide with electrons and scatter away in different directions (see Figure 1). This scatter may contribute as dose to the staff and visitors in the hospital. Factors that affect the scattered radiation are the size of the patient, field size, set X-ray parameters, and angle of the beam. Operation staff should be positioned far away from the tube and in a shielded position during exposure, when that is possible, or use lead aprons and other protections if they are in the room. X-ray rooms should be properly shielded to make sure that the scatter levels outside should be so low that it does not contribute too much to any once yearly dose limit. Due to this, the scattered radiation in different areas must be measured and evaluated.

To perform a scatter test, a water-equivalent phantom is normally put in the beam to represent a patient. The highest parameters that are clinically used should be set on the console, like the highest kilovolt and lowest inherent filtration. Measurements should be performed in areas of interest and measured with a very sensitive detector.

RTI Scatter Probe

Due to the measurement requirements above, RTI has introduced the RTI Scatter Probe (see Figure 2). It is a standalone, solid-state detector with a unique detector design, which makes it possible to measure either with an active area of 100 cm2 or 10 cm². This meets all the demands for leakage measurements. The detector is rugged and easy to carry. It can stand on its own, be used by hand, or be mounted on the included tripod or any other holder. The big detector area makes it very sensitive, which is a demand to measure on the low signals from scattered radiation. With its built-in energy compensation, the RTI Scatter Probe has flat energy dependence optimal to measure the wanted Air-Kerma Rate and ambient dose equivalent.

The RTI Scatter Probe can trig by itself when hit by X-ray and can be put in the X-ray room during exposure. A button on the back of the RTI Scatter probe can be pushed to activate the detector and move it around areas to find small leakages. Diodes on the back will light up proportional to the amount of registered radiation. It can also give a sound proportional to the level of the radiation.

The RTI Scatter Probe is connected to a tablet or a computer with a USB cable, and the data is presented and saved in the RTI Ocean Next™ software (see Figure 3). The same software can also be used with RTI´s other meters, to keep your measurements together, and for data to be presented in the same report.

Read more about X-ray leakage and scatter measurements

 

Björn Cederquist Key Account Manager at RTI Group. Björn is a Sweden-based medical physicist. He started at RTI Group, in
2008, at the R&D department working with detector design. In 2009, he moved to the Sales department and is now working mainly with the company’s key customers and sales and support in Japan and South Korea.

Published in EFOMP News, Issue 02/Summer 2021, page 72-73