Intrafraction Motion Management

Clear and consistent reference points

Fiducial markers provide clear and consistent reference points for the exact real-time location of the tumour target area. This is particularly important for tumours that might move or shift due to internal bodily processes, for example respiration or digestion.

Traditionally fiducial markers have mostly been used for Image Guided Radiotherapy (IGRT) to facilitate accurate patient positioning prior to each treatment session also known as Interfraction Motion Management, see section On-Board kV imaging for more information.

Technical development has made it possible to track fiducial markers in real-time during each treatment using kV-imaging equipment also known as Intrafraction Motion Management. The patients are positioned with the markers as reference and when the treatment starts kV-images are taken continuously during each fraction and a software is used to identify and track the position of the fiducial markers. Should the markers be detected outside the preset boundaries the treatment can be stopped, and the patient can be repositioned again.

Fiducial Markers are critical for new treatment techniques

There is an ongoing global trend towards using fewer fractions with a higher radiotherapy dose for each fraction known as SBRT, Hypofractionation or SABR. With a higher dose per fraction the target area and the margins used for the radiotherapy treatment becomes critical to avoid healthy tissue being exposed to high doses of radiation. Just one movement during a fraction with a high dose can cause both underdosage of the target volume as well as excessive toxicity in healthy tissue. This is why many ongoing SBRT or hypofractionation trials either require or strongly recommend the use of fiducial markers.

A publication from The University of Chicago Medical Center (ny länk till Clinical publications) showed that 36% of the prostate patients had more than 5 mm Intrafraction Motion of the clinical target. This can potentially lead to underdosing of the intended clinical target volume.

Another publication from Innsbruck Medical University showed that more than one third of the VMAT treatment sessions for SBRT of the prostate needed corrections due to translational displacement.  Real-time kV tracking of Gold Anchor markers can effectively mitigate intrafraction motion, and several systems are available on the market to support this capability, click on each of the links below to learn more:

• Varian TrueBeam Triggered Imaging & Auto Beam-hold
• Accuray Synchrony (CyberKnife & Radixact)
• Brainlab ExacTrac Dynamic
• Hitachi Real-time gated proton therapy (RGPT)
• SyncTrax

There are also some non-commercial kV-tracking systems developed for example Kilovoltage Intrafraction Monitoring (KIM) and SeedTracker.