Greetings all! I had a hunch that December would be a quiet month - a long slow march towards the festive season. Well far from it, been enjoyable and rewarding - I have no idea where each week has gone. I only wish this had been like this when I was a child; I remember clock watching for weeks wondering if the 25th December would ever appear!

RPS Radiotherapy Bunker Training

A key event this month has been running a RPS training event for managers of an industry leading linac manufacturer, supplier and installer of medical radiotherapy equipment. Although the training encompassed the usual suspects with respect to RPS training (the basics, dose limits, Ionising Radiations Regulations, ALARP etc) it also included a large module on linac bunker design. This module was presented as an overview of the subject (we were not trying to change them into shielding designers!), but we wanted to ensure all understood the basic requirements.

For this module we commissioned Chris from Grallator Limited to develop some new resource for Ionactive - a flyby virtual linac bunker. With this resource we firstly fly around the outside of the bunker as it grows from the ground upwards - we note the offices, waiting areas and storage space around the bunker in our virtual treatment centre.

 

We then take a pause at the entrance to look at the external active signage and consider the location of the Last Man Out (LMO) button.

 

We take a trip inside the bunker observing all the key features such as the emergency stops, locked engineering doors, last person out button, cameras and internal signage.


Here is a general view of the inside..




In this shot we consider the placement of the LMO (here shown as the alternative LMO). We discuss if this button should be placed near the exit (most bunkers we have seen) or at the furthest point from the exit (as shown here, next to the engineering door). We also consider the locking of the engineering door (and note here that the key has been left in the lock - a no no once in treatment mode).

We then exit the bunker and again fly above the facility - looking at plan and elevation views of the facility - noting the extent of the primary and secondary shielding.


This is the shielding shown in plan view

 



The shielding is then shown in side elevation





We then consider the shielding in 3d, by first looking at the total structure





And then we break it down into each part




I believe it to be an excellent example of using multi-media to ‘visit' a facility for the purposes of training - particularly when you might not have one on your door step.

The images you see in this blog are taken from the new resource. Currently there is no audible commentary - during the training I simply talked over the resource, stopping from time to time to discuss design issues with the delegates. As time allows we will work with Grallator to produce a script for audible commentary, so we can put this resource up on the web (like we do with all our similar videos and animations).

If you think the video animation of this resource would be helpful then email mark.ramsay@ionactive.co.uk and I will let you know when it is uploaded. Or, you can bookmark our YouTube page IonactiveConsulting and view it from there once it is uploaded.

Bunker Shielding Calculations

Been a busy month for shielding calculations too - not only number crunching for two different facilities, but also explaining the basic concepts in the above mentioned training course.



We have constructed a spreadsheet based model for the shielding required for a Gamma Knife. The Gamma Knife is a radio-surgical technique that utilises a large number of Co-60 sources built into a collimator array allowing precision placement of pencil beams around the head. The Co-60 sources are housed in a heavily shielded treatment unit which has a shielding door. With respect to dose rates outside the treatment zone there are really three circumstances to assess:

• Shielding door closed (lowest dose rates, but are above ambient levels, particularly around the back of the unit)
• Shielding door open and treatment couch out of machine - highest dose rates
• Shielding door open with treatment couch in machine (i.e. patient being treated) - intermediate level dose rates.

Unlike a linac which has an isocenter outside of the equipment, the Gamma Knife isocenter is within the machine. Typically, dose rates at this point are 3.5 Gy/min with a full load of Co-60 (about 200 sources, each around 1TBq when fresh). Once you know the basic characteristics of a linac (dose rate, patient position workload etc) it is relatively easy to calculate the required level of shielding (this being optimised). With the Gamma Knife, less is known about the photon energy outside of the machine.

With respect to ‘line of sight', if you were able to stand at the end of the treatment couch and look inside the machine with the shielding doors open, you would not be able to see any of the sources. This might therefore imply that all the photons outside the machine are scattered (depending on the shielding door and couch position) and therefore have lower energy than the expected classic double peaks of 1.17 and 1.33 MeV. However, it has been shown that there is a distribution of photon energies around the machine, including two lobes symmetrical about a centre line running through the machine,  foward of the shielding doors, which are very near full primary energy.

Therefore when designing shielding it cannot be assumed that all photon energies are less than primary, neither is it sensible to assume that all are at the primary energy (unless you want to build a shield with VERY high factors for safety). Therefore the solution is a mixture of classic shielding calculations (using Tenth Value Layers) modified by empirical calculations based on real measurements in and around real facilities.

Knowing the ‘workload' proportions of the above mentioned dose rate scenarios can also help in the design process (i.e. the highest dose rates are realised for the shortest period of time compared to the overall treatment period). Unlike the linac (and ignoring the short lived activations products of the higher energy machines), the Gamma Knife always produces residual levels of dose rate - particularly around its back end - these being slightly higher with the shielding doors closed (due to back scatter within the machine I believe).

Overall this is an interesting project to work on.

Thoughts for 2010...

So it's onwards and upwards (I hope) for 2010 - looks like being a mixture of familiar radiation protection related tasks and a number of new initiatives.

We have our first ‘R & N in CBRN' course ready to go for early February 2010. This course has been constantly evolving and now appears to be growing in popularity with the Fire & Rescue service (the course was originally designed for the Police Service). We believe this is an excellent step forward as multi-service training is likely to be more efficient. You can read more about these courses on our dedicated Contingency Training pages. (Sorry, the newsletter was delayed due to work in December, it will be released for early January 2010)

Our first general Radiation Protection Supervisor (RPS) course for 2010 takes place 25/26 January and is already almost full (which is unusual for January as we often find this is a quiet month). Although the course is constantly updated and tweaked from month to month, it will undergo a significant peer review and revision over the next 3 weeks to ensure it remains fresh and progressive. Although these courses are UK based they remain popular with delegates from around the world. In January 2010 we host delegates from the Ukraine and Syria who we will integrate absolutely with our UK based trainees. Find out more about our RPS training services by visiting our RPS Training page.

Talking of January normally being a quiet month - NOT - we are running a one day bespoke RPS fresher training course (NORM related) in Hull in the first week of 2010. Whilst our routine RPS training is always an interesting exercise (because our delegates are so diverse), we do enjoy developing and running bespoke courses.

Talking of bespoke courses - waiting to hear from the UAE to see if we are in the running to deliver a set of RPS / fresher training courses in the Gulf during February 2010.

Do check out this blog and our Radiation Resources pages for additional new material during 2010. We already have new animations in the pipeline - the first of which will be a virtual flyby (see we are into this now!) in and around an industrial radiography bay. This resource will be based around the panoramic radiography of large pipes using Ir-192. The animation will point out key features of the shielding, safety systems and warning signals. Also, since this bay is open-topped the resource will also graphically consider scatter from above the bay.



For up to date news on radiation protection, nuclear issues and related matters, Ionactive and a few odd things besides (Mr Ramsay does like his curry and Progressive Rock music), check out our Twitter Page www.twitter.com/ionactive. If you are not into Twitter you can still catch up with our updates on our home page and on this blog.


So - may I wish all visitors and clients are very good Christmas and all the best for 2010!

Well, I thought I was going to need to take the above picture for the kids before said ‘man' disappeared. Not sure what others feel, but we found the snow of the last few days very powdery and not the sort of stuff that is good to create large snow balls.

Anyway, just when I thought the melt had started .. this happens:



This is a quick shot taken out of my home office window. I am glad I turned back from a potential visit in South London today!

An hour later and its still going strong (a view from the back window of our house)



And finally, I cannot take pictures (I'm sure you can tell). This was my attempt at something 'arty' ... ahem back to the day job I think.

For some time we have made available our GM Tube resource on our Multi-Media Page. This resource was produced for us by Grallator Limited some months ago.

Well now it's available on our YouTube Channel: IonactiveConsulting.

You can watch Part 1 and Part 2 of the resource directly below now:

GM Resource Part 1



GM Resource Part 2



A few select images from the resource that we really like:

Getting to the heart of the matter ..

Why GM Tube is not best choice for pulsed radiation ..



The above diagram shows bunches of radiation, like that produced in a linac. If the dead time is longer than the pulse width duration of the detector, you will only pick up a single event (bunch) rather than the full bunch-worth of electrons or photons.

Therefore a GM detector is certainly not a good choice if you want to measure dose rate from a pulsed source of radiation. That said, we still use a GM based monitor when looking at dose rates around a linac bunker - buy only as an 'indicator' instrument. For formal dose rate measurements we will always use an Ion Chamber (current mode monitoring device).

Other online related Multi-Media Resource

As always, we do not endorse this - but like it all the same !

A GM Based DIY Neutron Detector



Producing X-rays from a Cheap Light Bulb!

Finally something for Xmas (as I have spent many an hour trying to get the Christmas Lights working every year!). Please do not try this at home.

Went to Marwell Wildlife Park today with the family. Alex (my older Son) is almost six so this was an early birthday treat.

Marwell, located near the south coast (about 10 miles from Southampton) is an excellent treat for all the family.There are loads of animals to see (obviously) but also a road train and small gauge railway to ride (see above)!

My younger son Ben really wanted to see ‘Melman' from ‘Madagascar' so we did our best for him!



Alex wanted to see the Tiger so we got a good view of him (I am glad the fence was in place!).



Here is Ben with the train - I think he wanted to take it home!



The 'Boys'



Now for some of my favourite creatures seen at Marwell!



And this ..



And finally this (kinda how I feel when deep into bunker shielding calculations).

This is taken from the IAEA event log.

Two incidents for you to consider this time.

The Incident - unnoticed public exposure (27/10/2009)

Ionactive Comment

Ok, so 0.12 mSv is not a significant exposure. On a recent trip to Scotland (flying) I recorded 5.5 μSv/h at 35,000 feet. So the public exposure is equivalent to perhaps 22 hours of flying. However, that is not really the point here - the control of the work area is appalling. Whilst the resulting exposure was small it could have been so much worse. I'm amazed that someone could have remained in the exposure area for 3 minutes before anyone realised that anything was wrong.

Suppose the member of pubic had been only 1m from the source - their exposure would have then been more like 1mSv (the public dose limit in most parts of the world). Let us take that further, suppose the member of public had been only 10cm from the source - then we are looking at around 108 mSv - way over employee annual occupational dose limits (which are set at 20 mSv per year in most parts of the world, and 50mSv in some states in the US). This assumes that the exposure time was still three minutes.

And it gets worse ....

The Incident - worker overexposure (12/11/2009)

Ionactive Comment

We know less about this incident (e.g. source type, distance from source and exposure time). However, like the first example involving public exposure, there seems to be a break down in procedural control.

We have been working with a company recently on the design and build of a number of radiography bays - this engineered approach to safety must always be the goal to achieve. What the two examples show are the dangers of Site Radiography - here you are only relying on procedures and local shielding to restrict exposure. That said, suitably qualified and experienced persons should have no trouble in undertaking site radiography in a safe manner - we work with industrial radiographers who do this every day - their work practices are exemplary.

So what has gone wrong here? - the example show that these incidents are not restricted to certain areas of the world - Peru and the US both have issues (and I am not discounting the UK either).