From Lead Glass Windows to Real Time Motion Management in Radiotherapy

Sometimes the best ideas are considered too simple!

As discussed in past blogs I have always tried to be creative when it comes to designing products to assist in the day to day running of a busy radiotherapy centre but perhaps my RTrak system was misunderstood!

In 1980 when I started as a DCR student at the Middlesex Hospital every megavoltage radiotherapy bunker had a solid lead glass style window (and if I recall Barium based glass too?) that was then the gold standard in checking that the patient was still where you put them! These windows were designed with patient safety in mind even in the 1950s as this article from Mount Vernon below shows when 2 new Megavoltage bunkers were being designed.

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It states that:

“The design of buildings for high energy radiotherapy units requires an early consideration of the means whereby the patient may be kept constantly in the view of the operator during treatment:

Such windows provide direct vision, their use involving a minimum of effort on the part of the operator, while the apparent distance between patient and operator is not increased.

The design of both treatment units is such that the patient, and particularly the region under treatment, will always occupy about the same position relative to the operator, so that the window area can be quite small”.

CCTV eventually arrives

Eventually CCTV cameras where installed in essentially every radiotherapy treatment room with a TV screen located by the control console that you would use to check for unwanted patient motion or for them to walk out of the room behind you when we asked them to keep very still and confusingly say “off we go then”.

pic: CCTV system set up

In the days prior to “auto-sequencing” of treatment fractions and then IMRT and VMAT each beam of each fraction was delivered manually with you walking in the room to “pin and arc” each beam. Including taking the patient in and then out after the treatment was completed this amounted to 10 visits to the machine down the long maze for a 4-field block bladder! That certainly kept you fit but also allowed you to check the patient was in the correct position for the vast majority of the treatment.

The advent of IR(ME)R regulations that made it an criminal offence to treat the wrong patient and also the wrong part of the patient made safety and security more important with CCTV taking on most of that key role although having to stare at a TV screen all day long was not the most ideal use of radiographers time for what has always been a relatively scarce human resource.

The IMRT and VMAT innovations have certainly improved and enhanced the accuracy and speed of modern radiotherapy but perhaps initially at the expense of patient safety in that each fraction is delivered without any intra-fraction check of the patients position and so keeping very still or being immobilised in a mask or vacuum bag was critical.

Even then the CCTV played a vital role with the camera zoomed into the laser and tattoo to check for movement. I know some radiotherapy managers who would perform their own patient motion governance checks by deliberately standing in front of the CCTV monitors and blocking the view to ensure staff actually did watch the patient at all times!

Every radiotherapy bunker around the world has a CCTV system and so for almost 40 years very little changed in this respect until the recent improvements in motion tracking technology, an innovation that I certainly believe in and will reflect on a little later in this blog.

My too simple idea!

Q. Why not use the CCTV system to track unwanted patient motion?

A. Yes you can and also provide an alarm if the patient moves out of a simple pre-set tolerance.

I designed a product called RTrak, a simple upgrade to any existing CCTV system that confers basic motion tracking and an alarm app to these systems by capturing a small, little to no-cost and consumable marker simply stuck on the patient and then tracking it in real time!

This is the RTrak paper that was published in the SCoR magazine Synergy.

Title: RTrak and IR(ME)R complaince with reference to unwanted patient motion when undergoing radiotherapy

The Society of Radiographers have recently published “Have you paused and checked” posters. A radiotherapy IR(M)ER checklist for operators about to treat a patient

The posters have been published to serve as a handy reminder for therapeutic radiographers.

They are designed in a PDF format to allow for easy downloading and printing for display in the department as required. Sections of text can be edited to reflect local protocols

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Pic: IR(ME)ER poster

RTrak is an innovative alarm system designed by Duncan Hynd Associates Ltd and supplied in the UK by Imaging Equipment Ltd that assists departments with IR(ME)ER compliance and passively monitors unwanted patient motion through the exisiting CCTV system.

The pause and check posters clearly state that while treating the patient they should be watched at all times, a basic safety and security procedure for all patients undergoing radiotherapy usually using conventional CCTV systems located in the bunker. While zooming into the patient and visualising them on the TV screen at all times is a requiste of IR(ME)ER, the possibility exists where unwanted patient motion may ocuur and may not be noticed in real time.

RTrak, through the use of a simple disposable patient dot marker, tracks the postion of the dot at ALL times, and the system will alarm should patient motion exceed simple preset distance and time tolerances. It requires no calibration and provides radiographers with information on the actual patient postion at all times, allowing them to make immediate, informed decisions as to whether to stop or continue the patient’s treatment.

This low cost and simple to install upgrade adds a patient motion alarm to the existing CCTV system and enhances patient safety and security while undergoing radiotherapy treatment.

How does RTrak work?

The disposable marker is visualised on a small PC located next to the CCTV viewing screens and shows up as a black dot. The radiographer simply has to zoom in and click on the marker.

Once the marker has been clicked on and detected it will turn blue and show a cursor and green circle. The blue dot is where the patient should be, the circle is where they actually are.

If the patient moves, the green circle will move away from the dot but providing the patient does not move more than the pre-defined tolerances, the alarm will not sound.


If the patient moves out of tolerance the green dot will turn red and the system will alarm. If the patient moves back into the correct position the alarm will stop.

Frequently asked questions and answers:

Will the system slow us down, we have a very busy Linac? No, it only takes a few seconds to capture the marker and then switch the beam on as usual.

Does the system record each and every treatment? No, the system is a simple alarm app for CCTV and detects unwanted motion in real-time.

Do we have to buy a new CCTV system? No, the system integrates into the existing system and can be installed in minutes.

Will the installation require down time for our Linac? No, we simply install a splitter into the existing CCTV cable connector.

How do we calibrate the system? The system does not need to be calibrated and works reliably in any lighting condition for ease of use

How accurate is the system? The system can be used in real time with mm accuracy or with set time delays measured in seconds.

Does it have to be used for every patient? No, it may not suit some treatments for instance when breath-hold is used or moving couches are installed but whenever you use the CCTV, RTrak simply adds an audible alarm if the patient moves out of your pre-set tolerance!

Are the patient dot markers expensive? No, they are disposable and very low cost.

So why did the RTrak system not catch on?

I really do think that this idea was too simple and too low cost. When demonstrating the system, it just took a second to turn the CCTV system into a motion tracking and alarm device and to many this was a bit of an epiphany. The app ran on a small laptop and ran quietly in the background during beam-on time, monitoring all the time but only alarming if the patient moved out of a simple tolerance and alerting the busy radiographer that there might be an issue in the room. You could still watch the patient on the TV screens that came with the original CCTV and it was up to you whether to intervene or not.

This meant that IR(ME)R regulations where always met in that you could show that the patient had not moved and so a leap forward from conventional CCTV monitoring.

If you enter the room after IMRT and the patient has moved, when did they move during beam-on and how much? Did this compromise the treatment? You don’t really know and so potentially an major issue under IR(ME)R regulations. Patients do move and unwanted patient motion was and is a grey area in our profession that is now being addressed but not right across the board.

Not one radiotherapy centre I have met will remove their CCTV system but none seem to want to add a simple motion tracking app as an upgrade. In fact, many people I spoke with wanted it to be far more complicated and for us to add Linac gating and couch control, breath hold software, treatment archives, automated set-up and potentially intra-fraction organ motion among other features and so they missed the simplicity of the alarm concept or the fact that the RTrak app is only a few thousand pounds to install.

However, in radiotherapy over the last 50 years or so we have transformed patient safety and security from a simple lead glass window to new systems that can now automate patient ID, perform accessory checks, assist in patient set up and provide motion management during beam-on for all IMRT and VMAT treatments.

So where does that leave the RTrak concept?

There are over 14,000 radiotherapy machines in the world according to the IAEA of which the majority have a bunker, CCTV but no motion tracking facility at all to enhance patient safety and security and so the market is still very much there. Is anyone out there interested?

If you are interested in more information on RTrak please let me know by email at

Timeline for motion tracking development

I mentioned at the start I would briefly look at the progress of patient motion tracking and so here is a brief summary of some of the past and present developments in this field:

Lead glass windows.

Walking in and out of the bunker 10 times to deliver one 4 field plan and checking the patient position by eye.

CCTV systems with pan, tilt and zoom options.

OSIRIS camera-based system that acquired planning contours using existing room lasers with an in-bunker beam-on mode to check the correlation of those contours.

Brain Lab ExacTrac used retroreflective fiducial markers and x-rays but now with a new thermal camera to capture surface data and correlate that to internal anatomy.

CyberKnife from Accuray uses a robotic design, coupled with real-time imaging and tracking while adjusting for tumour or patient movement during treatment.

Varian RPM is a real time position management system, video based with Infra-Red lighting and reflective markers on a chest mounted cube with a role in breath hold.

Elekta ABC provides for the internal immobilisation of respiratory motion using a breathing tube.

Vision RT offer Align RT that uses 3D stereo-cameras to create a skin surface reconstruction that simply compares that in real time with a prior “ideal” treatment position.

C-Rad Catalyst uses lasers to create a tracking, set up and motion management system.

Micropos RayPilot inserts a transmitter surgically into the prostate that communicates with a receiver on the couch to control inter and intrafraction prostate position.

Varian market the Identify Guidance System that integrates among others patient ID, the correct treatment accessories, auto set-up and motion management using proprietary surface technology.

Of course, many of these systems incorporate Deep Inspiration Breath Hold software or DIBH for reducing cardiac and lung toxicity in the treatment of breast cancer while advances in kV imaging in 4D allows imaging of the tumour prior to treatment.

This is not intended to be a conclusive or comprehensive list but highlights the considerable R&D work that has gone on recently in this field in a short space of time.

One potential conclusion

The innovation of the MRI Linac is probably the holy grail for motion tracking with truly adaptive radiotherapy in real time now a clinical reality.

Pic: Elekta Unity MRI Linac

As Elekta mention: Unity is a state-of-the art MR-linac that is setting a new standard for personalized radiation therapy. Elekta Unity provides the ability to reshape the dose based on daily changes in shape, size and position of the tumor and surrounding healthy anatomy and then enables accurate dose delivery with real-time visualization of the tumor.

For more MRI Linac information click here:

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Duncan Hynd August 2019