What is the recommended HVL for x-ray tubes operating above 120 kVp?

The recommended half-value layer (HVL) for x-ray tubes operating above 120 kVp is 4.1 mm of aluminum. HVL refers to the thickness of a specific material (in this case, aluminum) that reduces the intensity of the x-ray beam to half its original value.

As the energy of the x-ray beam increases, higher HVL values are necessary to adequately filter out low-energy photons that contribute less to image quality and increase patient dose without providing useful diagnostic information. For x-ray machines operating at high kVp settings, such as above 120 kVp, regulatory and safety guidelines specify a minimum HVL of 2.5 mm Al to ensure adequate filtration and optimize radiation safety. However, certain standards—such as those established by the American College of Radiology and the Radiological Society of North America—suggest even higher values for increased protection, which is why 4.1 mm Al is identified as the recommended HVL in this context.

By ensuring that the x-ray machine operates with this level of filtration, medical facilities can ensure optimal patient safety while maintaining diagnostic image quality, as it helps attenuate the beam effectively and reduce unnecessary exposure to radiation.