STP Reflections| 15 weeks of radiotherapy

My MR placement at Addenbrookes set the bar very high.  A career in MR has a great deal of appeal; given my research background, it feels like a natural fit.  

Or does it? …  

Radiotherapy is what drew me to medical physics and to the STP; it has already been defined as my specialism.  Before applying I spent some time in brachytherapy at Guy’s and St. Thomas’ and I remember being overrun with excitement talking to the trainees working there.  If any of the three trainees, who may now be qualified clinical scientists, are reading this then please accept my sincere thanks! This also extends to Sarah McElroy for hosting and organising my work shadowing in the first place.    

Before I begin, I’d like to say a little bit about what happens when you get through the online screening test for the STP and the, in my opinion, horrendous speed dating style interview.  Candidates are ranked according to how well they performed across both of these assessments and each candidate is asked to list their hospital preferences.  At the time, I was convinced that I wanted to do radiotherapy so rather naively I moved all of the pre-defined radiotherapy specialism placements into the “accept” column.  Looking back, this probably had no impact whatsoever on my chances of getting a place as I had already made it through the interview.  This may be a worthwhile thing to bear in mind for anyone making an application.  

The upshot of this is that radiotherapy is my specialism and Ipswich is now my home.  This meant relocating from the North East, where the PhD stipend went a long way and moving the contents of my flat into my parent’s garage (where it still is).  

The following describes some (there are many) of the memorable pieces of my radiotherapy placement; for the benefit of any as of yet unconvinced STP applicants or any interested spectators (Mum).  

My first week happened to be Healthcare Science Week and, given that physics has a reputation for shielding itself from the public, I figured that I had to do something to promote the role of physics in a successful radiotherapy department.  Armed with suitable paraphernalia, most kindly and at the last minute donated to me by the Institute of Physics and Engineering in Medicine (IPEM), I set about putting up a stand in the foyer outside the department.  Despite being desperately far from my comfort zone, this actually turned into an excellent experience.  I had a steady drip-feed of interest from patients, staff and members of the public, perhaps because IPEM also agreed to fund the purchase of some sugary incentives.  But I think, in general, the experience served as an apt ice­-breaker between myself and the department.  I should also state that there is no shortage of inspiration that can be drawn from cancer patients.  

Radiotherapy physics is subdivided into two main sections, dosimetry and planning, with a small amount of radiation protection.  

This wouldn’t be a blog post about a physics specialism if I didn’t waffle about metrology.  The word dose is familiar to us all; when you take an antihistamine for your hayfever some boffin at Big Pharma has worked out the mass of drug required, and how often you need to take it, to reduce eye irritation and snot build-up without compromising cognitive function.  When we talk about a dose of radiation what we in physics infer from that is the energy deposited to a mass of tissue as a consequence of that irradiation.  For X-rays, what we are really interested in is the energy imparted to ionising particles.  It turns out, rather fortunately, that liberated electrons are an effective means of destroying chemical bonds in important biomolecules, like DNA, and therefore killing tumour cells.    

But the interesting thing is how we measure this dose of radiation.  When weighing out a mass of drug the balance gives you a direct measurement, in grams, of the quantity you are trying to measure.  If we want to measure the amount of energy imparted to tissue then the number of balances that can do the job are few and far between.  In fact, there is only one that matters, and it’s an exquisitely sensitive graphite calorimeter, which measures the temperature change as a result of the dose of imparted energy, and it is kept at the National Physics Laboratory (NPL) in Teddington.  No hospital could afford to store, staff and maintain such an instrument, nor would they want to.  Instead, radiotherapy physics departments use ionisation chambers, which measure the charge-separated in the air contained in the chamber, as a result of the radiation beam. These ion-chambers are calibrated against the NPL primary instrument.  As a budding physicist, I find this extremely satisfying.  It is as if all hospitals up and down the country measure the output of their dose machine with the same single instrument – brilliant!     

On top of the fact that we cannot measure absorbed dose directly with our instruments, we cannot measure the dose actually delivered to the patient.  It is not as if we can stick our ion-chamber in the prostate (that would be brachytherapy levels of barbarism!).  Instead, we have to take a reference image of the patient anatomy and estimate how the beam will distribute dose if it passes through this much skin, fat, bone, tumour etc. This is where treatment planning comes in.  This area of radiotherapy physics is moving forward rapidly.  Evermore complex dose delivery methods are being commissioned. And these, in turn, require ever more sophisticated algorithms to compute the dose distribution.  One of my physics mentors, who is turning out to be one of my favourite teachers, once said to me Treatment planning is not a battle, it’s a war! 

Whilst I completely agree with that sentiment, at 7pm on a Friday when all that stands in the way of your weekend is an excess 0.1Gy lung dose, it’s backs to the wall.  However, there is a great deal of beauty in the orchestra of gantry and multileaf collimator motions that sculpt dose to the geometrical confines of tumour whilst sparing normal tissues.    

I mentioned my admiration for the diagnostic radiographers in the MR department at Addenbrookes. That respect has reached new heights having watched the treatment rads at Ipswich.  Not only do these guys and girls have to negotiate all this physics, but they also have to deal with patients with complex emotional and physical needs. The most sophisticated instrumentation and planning algorithms in the world are all in vain if you put the patient in the wrong position on the couch.  A tough job – one I certainly could not do!  

I’ve been hugely impressed by Varian – the company that makes the machines, patient handling and treatment planning software at Ipswich.  Towards the end of my rotation, I was excited to discover that the treatment planning system has a python developer interface.  The list of options for filling my elective placement gets longer by the day.  

One final thing, which should be of great interest to prospective STP applicants, is that there is money set aside by the NSHCS for travel and conference attendance.  I’ve just got back from the 4th Christie Advanced Radiotherapy Summer School having had a superb run-down of all the sexy bits of radiotherapy.  I heard from some huge names in the field talking about novel indications for brachytherapy, the role of MR in radiotherapy, the clinical need for stereotactic ablative radiotherapy and the merits and (mostly) pitfalls of proton over photon therapy (should anyone wish to debate that last statement with me please tweet at me – @Stubbington2309).  I also had the privilege to see the MR-LINAC facility at the Christie; a miraculous feat of engineering, but a machine still finding its place in the UK radiotherapy patient pathway.    

Perhaps most importantly, I have been taken aback by how friendly the Ipswich department is!  I think I had the right to be nervous; I’m going to work with and ultimately pester the physicists, radiographers, oncologists, domestic and administrative staff for the next two and a half years!  Because the department is on the smaller side in the radiotherapy league table, I have had what amounts to a series of one-to-one tutorials to guide me through some conceptually challenging physics.  I knew I would be happy on the STP programme, but I didn’t think I could be this happy; I no longer get that Sunday night feeling about work the next day.  For that, I am truly grateful.   

Upon reflection, I’m delighted to say that the radiotherapy specialism, with a soft spot for MR, is the right one for me.  At least to within one standard deviation of the mean of my preference taken at randomly sampled intervals.  I’ve definitely landed on my feet here in Ipswich.  Suffolk and the Ipswich Hospital radiotherapy department are lovely and I’m making considerable headway with the work-home life balance; I’ve dusted off my guitar and taken up squash.  I have to pinch myself every morning to remind myself that I have a place on this training scheme and I can’t wait to get back and tackle the radiotherapy specialism challenges that lie ahead.  

In the meantime, there is the small matter of radiation protection and imaging with ionising radiations to attend to…  

Author: Liam

Trainee clinical scientist at the Ipswich Hospital.

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