“Blue has no dimensions, it’s beyond dimensions, whereas other colours are not. All colours arouse specific associative ideas while blue suggests at most the sea and sky, and they, after all, are in actual, visible nature what is most abstract.” Yves Klein – Artist.
Yves Klein was a French artist and an important figure in post-war European art. He was a leading member of the French artistic movement of Nouveau réalisme founded in 1960 by art critic Pierre Restany. This painting is an “Untitled Anthropometry” and follows his trend of using Cobalt blue paint.
“The Blue metal”.
For well over three thousand years cobalt was initially coveted for its blue colour. Ancient Egyptians decorated ceramics and glassware with blue pigment derived from the metal and it’s still used in paint today as above.
Being strong at high temperatures allows it to be incorporated in many crucial alloys, rechargeable batteries, especially those in mobile phones and electric cars, while cobalt’s other uses include aero-engines, medical devices, and corrosion resistant super-alloys.
Much of the extracted cobalt we use today is a by-product from other mined minerals such as nickel or copper, with over half of the world’s supply stemming from nickel mining. In Africa in the ex-Belgian Congo, now the DRC this is often carried out by hand using very young children in extremely dangerous and unhealthy working conditions, and so human rights abuses are an unfortunate by-product of the supply chains.
So why did Cobalt become so intrinsically linked to radiotherapy? A very brief history.
The first recorded patient treated by Cobalt teletherapy was in 1951.
Cobalt-60 is produced by neutron bombardment of stable cobalt in a nuclear reactor. Small nickel-plated pellets of the radioactive metal are then loaded into a sealed alloy cylinder that was around 2cm in diameter and named very originally, the “source”. Using high activity radionuclide meant the source could be manufactured as small as physically possible, reducing the penumbral effect on the beam due to the physical source dimensions. Cobalt-60 decays continuously and its half-life is 5.26 years and so needs replacing every 4 to 5 years to keep treatment times optimally short. The first recorded patient case treated with Cobalt-60 was in 1951.
The original “Cobalt Bomb” unit.
In the UK the first Cobalt-60 Teletherapy unit was installed at Mount Vernon Hospital in 1953 where the ‘Theratron’ was the gift of a Canadian philanthropist, Mr.Jack McConnel, to the British Empire Cancer Campaign while in Yorkshire, The Hunslet Engine Company turned their hand from making steam locomotives into radiotherapy telecobalt units at around the same time and initially installed these at Cookridge Hospital in Leeds with the first rather disreputably named the “Cobalt Bomb”!
This is not to be confused with the hypothetical explosive device, which served as the basis of the “doomsday machine” in the classic 1964 film Dr Strangelove, who would employ radioactive cobalt to create unusually intense long-lived fallout, something the Soviet Union has allegedly been conceiving right up until the present day.
Furthermore, at this time it seems these machines cost around £15k plus £5k for a source with a lead time to installation from order of around a year, in today’s money that is around £225,000!
These new rotational and iso-centric units were more accurate that those older tele-therapy radiotherapy machines that simply translated head position even though the sheer weight of the rotating shielded head meant that there was a limited but real amount of head sag to take into account dosimetrically!
Cobalt-60 became popular because of the high cost and limited supply of Radium and had a useful mean beam energy of circa 1.25 MeV, (actually two differing energies of 1.17 and 1.33 MeV are released) a clinical dose rate of around 1 to 2 Gy/Min at a meter for a brand new source of specific activity around 400 Tbq and so quickly became the gold standard in a new era of cost effective and reliable “Super-Voltage Radiotherapy”.
A paper published by Radiation Therapist Dr Paul Strickland in 1958 can be accessed here that reports on their initial experiences with their machine. I actually worked closely with Paul when I was a radiographer at Mount Vernon where we made what were really remote after-loading caesium moulds for largely scalp based skin tumours: https://pmj.bmj.com/content/postgradmedj/34/394/419.full.pdf
Historically, Radium had been in general use as a therapeutic agent since its discovery. It has been of particular value for intracavitary therapy and interstitial application, either in the form of needles containing the radium element or gold radon seeds, which are left in situ. Its employment on any considerable scale in teletherapy, which required large quantities for an adequate time/dose relationship, has been prevented by the relative scarcity of the element and its high cost. Caesium 137 become momentarily fashionable as a replacement for Radium but Cobalt 60 has proved ideal for the purpose of routine radiotherapy teletherapy treatment.
Source design and safety systems
One downside of the technology was that source could become stuck in the “ON” position and so various safety systems were designed, some simply meant pushing an exposed rod connected to the source back in! These were often exposed using air-pressure and so if that failed so did the source movement.
Most Cobalt machines as discussed, housed the radioactivity in the form of a cylindrical source of circa 2 cm diameter, mounted directly on a steel cylinder or located in a rotating drum held against a helical spring. “Source on” position was achieved by a simple motor operating against the spring tension. Both types of systems had a failsafe mechanisms to bring the source back to the “OFF position” in case of power failure and for patient safety some machines even had a facility for total closure of the diaphragms electrically to a 0 cm × 0 cm field size while on others the table locks were released, the table then became free-floating and could be longitudinally pulled backward or translated laterally to remove the patient more quickly.
Some centres would ask the patient to get off the couch themselves and would leave some steps close to the machine and couch in case of the source sticking and then reduce the collimator size manually. Either way it was important to get the patient out of the room as quickly as possible.
London was not really nuclear free, and no one seemingly told Greenpeace who started out in 1971.
According to Wikipedia, a nuclear-free zone is “an area in which nuclear weapons and nuclear power plants are banned. The specific ramifications of these depend on the locale in question”.
It continues that Nuclear-free zones “usually neither address nor prohibit radiopharmaceuticals used in nuclear medicine even though many of them are produced in nuclear reactors. They typically do not prohibit other nuclear technologies such as cyclotrons used in particle physics”.
They also state that several sub-national authorities worldwide have declared themselves “nuclear-free”. However, the label it says is often symbolic, as nuclear policy is usually determined and regulated at higher levels of government: nuclear weapons and components may traverse nuclear-free zones via military transport without the knowledge or consent of local authorities which had declared nuclear-free zones.
The Middlesex Hospital in the early 80’s was certainly not a nuclear free zone!
We had 4 machines where I trained as a radiographer containing Cobalt-60, and so even in those days a nod to health and safety meant not leaning on the machine head (especially male radiographers) when operating it for any length of time as these units were always “ON” even if the source was not exposed.
The Mobaltron and Theratron were “rotational but non-isocentric” as were many “Cobalt Units” with a SSD of 80 cms while the Cobaltron Minor was a short SSD machine useful for treating neck nodes and mets while the Cathetron, a forerunner to the LDR and HDR innovations offered remote after-loading of Cobalt sources for mainly Gynaecological cancers and insertions.
The Theratron 780 C came all the way from Canada where the Atomic Energy of Canada Limited or AECL in Ottawa produced both the Cobalt-60 at their Chalk River isotope production facility and also the radiotherapy treatment machines themselves. With source activities likely to have been between 5,000 and 10,000 curies in those days the doors to the bunkers would have to have been securely locked overnight post 9/11.
Their treatment planning system Theraplan, was based on the renowned work of local Toronto Physicist Jack Cunningham and also very popular worldwide. AECL created two business units Theratronics and Nordion in the eighties, becoming two distinct commercial arms, one medical and one industrial and had many UK installations of both planning and treatment delivery products. The other machines we had were manufactured in the UK close to Gatwick by TEM who were eventually taken over by Varian. The further main supplier of Cobalt-60 machines was GE in France who made Alcyon units. I ended up working successfully for Theratronics later in my career and will come to that shortly.
Some space oddities!
While primary deposits of cobalt originate in nations such as Australia, Cuba, and the Philippines, the largest reserves as discussed earlier are in the Democratic Republic of Congo where it’s likely that around 4 billion years ago asteroid impacts re-infused the Earth’s depleted crust with rare metals like gold and cobalt but in the 80’s there was lots of it in London and it was used in very innovative ways!
Here are two good examples:
The Royal Free Hospital tracking cobalt unit for innovative conformal therapy
This machine was located at the Royal Free hospital in London, the then Head of Physics being Terry Davy. Terry was outwardly dour but an extremely humorous and personable Medical Physicist once you got to know him and who was very welcoming to “sales reps” once he ascertained you knew what you were talking about and were in fact a radiographer! I even cold called one day when passing and he made time to see me and a cup of tea, something I am sure would not happen today!
Terry was adamant in the 80’s that the future was all about “inverse planning” whereby he wanted to tell the planning system what he wanted to achieve dose wise and it should work that out. This prescient view of the future of radiotherapy was also very much part of the unusual “home built” tracking cobalt unit. This delivered conformal radiotherapy using an up and down, longitudinal and lateral automated moving couch located on a track and a rotating or arcing head which was used to shape the irradiated volume to match the tumour volume in three dimensions using synchronised shielding. This was long before the advent of MLC and so to track the entire tumour was very innovative to say the least!
A typical case as discussed in the paper below would be the treatment of an oesophageal tumour, where the technique was used to compensate for an irregularly shaped tumour in a part of the body having a large variation in cross section. A second example would be how technique coped with a tumour having a regular shape but having an awkward location in the body.
The method had the additional advantage that corrections could be made for variations in dose rate along the tumour axis resulting from changes in body outline and the presence of in-homogeneities.
You can read much more here if you want to:
Royal Marsden Hospital, Sutton and its double headed cobalt unit for Total Body Irradiation.
As there were no commercial units available to meet the RMH TBI unit specification they decided to make their own! The specification of the TBI unit and mechanical layout was for the unit to consist of two cobalt sources housed in two vertically aligned Theratron 780 heads made by AECL in Canada and capable of independent movement and operation.
The SSD for each source was to be at least 3.5 m at 25 cm above floor height, variable on both sources between 2 m and 3.5 m, with field sizes of 2 m × 65 cm at 3.5 m and asymmetrically at 2 m SSD with a 2 m × 65 cm field. Low dose rates were to be obtained by beam attenuators and the longitudinal collimators worked independently. The couch was constructed with no metal in the field area with a vertical movement of 0−20 cm above the floor.
The patient was treated both anteriorly and posteriorly essentially at the same time making the dosimetry far more accurate than two individual, separate set ups and out of interest, when I was working with Theratronics we were responsible for supplying and installing new radioactive sources for the two heads and so got to know the team in Medical Physics and Bioengineering well.
Source changes and serious accidents.
When a Cobalt-60 source was around 5 years old it would be changed for a higher activity one. This involved shipping the new source in a registered container to the hospital and assembling a block and tackle in the bunker. The spent source would be pushed out and into the raised container and the new one then pushed in. This simple sounding technique was not without problems, especially when the source was in the unshielded position between container and treatment machine head, where you did not want it to stick and you did definitely did not want to use your fingers!
The source container or BU was romantically called a “PIG”, shipped back to the manufacturer and stored in a very deep swimming pool for an undefined period of time to decay and or be safely recycled. I visited one of the huge baths in Canada and the Cobalt did in fact glow blue, I am not sure if this was photon interaction with the water or its natural colour, perhaps someone will tell me!
Cork in Ireland was a Nuclear Free Zone!
I do recall changing the source of the Theratron at what was then the Cork Regional Hospital and the shipping container seemingly being very loosely strapped by the Irish shipping agent to an ageing open “flat-bed” pallet lorry and passing the above sign and thinking “if only they knew” as up to 10,000 curies of potentially deadly radionuclide entered town! It didn’t fall off fortunately.
This radionuclide as we are all aware is very safe when in trained hands but accidents do happen either due to the sheer weight of the hardware required or the invisible threat due to the “hidden” radioactivity. The first example here is when a 1.3 tonne Theratron head fell on a patient killing them and then some further examples of Cobalt-60 sources ending up in the wrong hands, those of mainly ignorant and illegal scrap metal dealers:
I have included some further “lowlights” below from the list of world-wide civil radiation accident database on Wikipedia when Cobalt-60 (or other radiotherapy radionuclide) ended up in the wrong hands:
1982 – Cobalt-60 became recycled into steel rebar and used in the construction of buildings in northern Taiwan, principally in Taipei, from 1982 through 1984. Over 200 residential and other buildings were found to have been built using the material. About 7000 people are believed to have been exposed to long-term low-level irradiation as a result
1983 – Ciudad Juárez, Mexico. A local resident salvaged material from a discarded radiation therapy machine containing 6,010 pellets of 60Co. The transport of the material led to severe contamination of his truck. When the truck was scrapped, it in turn contaminated another 5,000 metric tonnes of steel to an estimated 300 Ci of activity. This steel was used to manufacture kitchen and restaurant table legs and rebar, some of which was shipped to the U.S. and Canada
1987 – In the Goiânia accident, scavengers broke open a radiation-therapy machine in an abandoned clinic in Goiânia, Brazil. They sold the kilocurie caesium-137 source as a glowing curiosity. Two hundred and fifty people were contaminated; four died.
1998 – Istanbul, Turkey – two sealed transport packages for spent 60Co teletherapy sources from a shipment of three planned for export in 1993 were instead stored in a warehouse in Ankara, then moved to Istanbul, where a new owner sold them off as scrap metal. The buyers dismantled the containers, exposing themselves and others to ionizing radiation.
2000 – A radiation accident occurred in Samut-Prakan Province, Thailand. The accident happened when an insecurely stored unlicensed cobalt-60 radiation source was recovered by scrap metal collectors who, together with a scrapyard worker, subsequently dismantled the container, unknowingly exposing themselves and others nearby to ionizing radiation. Over the following weeks, those exposed developed symptoms of radiation sickness and eventually sought medical attention.
As suggested in my main blog headline we are moving slowly from tracking Cobalt to tracking Criminals as reported here in Mexico in 2013.
“Mexican Cobalt-60 robbers are DEAD MEN, say authorities – Bungling bandits liable to have sustained fatal rad dose in truck snatch blunder”!
“Mexican troops have recovered a stolen shipment of radioactive Cobalt-60 isotope, abandoned by truck thieves who face the risk of a slow lingering death from radiation poisoning.
A truck carrying a substantial quantity of the radioactive isotope Cobalt-60 from a hospital in Tijuana to a waste centre was robbed by armed bandits in central Mexico on Monday. Its drivers were sleeping at a petrol station at the time of the carjacking, which bears the hallmarks of an opportunistic theft by crooks who had no idea what they were getting themselves into!
The stolen Volkswagen cargo truck was found abandoned 40 km from the scene of the robbery in a field near the farm town of Hueypoxtla on Wednesday with the stolen Cobalt-60 found on the ground, outside its protective shielding”.
The Cobalt Unit’s demise in post millennial UK.
In 1994 and very much against the trend at this time, St Thomas’ Hospital in London purchased two brand new, matched Theratron T1000 Cobalt units directly from myself and Theratronics.
These were fully computer controlled, isocentric with 100 SSD, had asymmetric jaws, high activity sources and linked directly to record and verify systems and so were essentially Linacs in disguise but considerably cheaper and reliable at that time with less burden on the hospitals’ engineering and physics department.
Bearing in mind that up to 40% of a busy London Hospitals workload at that time was breast radiotherapy and the fact that many other tumours both primary and secondary were perfectly treatable with Cobalt-60, this made clinical and financial sense. However, these were the last two Cobalt-60 machines installed in the UK and if you look at the Cancer UK 2001 radiotherapy equipment census and at the turn of the century you will see that in England and Wales there were 250 Linacs and 25 Cobalt Units and so around 10% were left but by 2010 they were all decommissioned and the 60 year long Cobalt-60 Super-Voltage era came to an end in the UK.
Uganda, Africa 2020. The installation of an Indian Government funded and modern Bhabatron Cobalt unit under the remit of an IAEA initiative has now meant that radiotherapy services have restarted in Uganda following their collapse in 2016.
From Emergency to Expansion: With IAEA Support, Uganda Recovers and Improves its Radiotherapy Services
In early 2016, the sole functioning radiotherapy machine in Uganda broke down, leaving 40 million people in this East African country without access to this life-saving treatment. Following a request from the government, the IAEA provided expert services, staff training and procurement of equipment through its technical cooperation programme, leading to the procurement and installation of a new machine and the re-establishment of radiotherapy services in the country.
Agency support continued throughout 2016 and 2017, and a new, national cancer control project—launched in January 2020—now promises to continue the path towards stronger, more accessible cancer therapy services.
The future of Cobalt-60 in the UK for radiotherapy treatment delivery
Gamma Knife from Elekta for SRS.
The Gamma Knife collimator system consists of 192 Cobalt-60 pencil-beam style sources, divided into eight sectors that can be individually positioned to any of four states: 4 mm, 8 mm, 16 mm or off. During treatment, sources are positioned using the sector mechanism to generate the desired radiation beam and enable the treatment of very complex structures. There are over 300 installations world-wide.
MRIdian from ViewRay
In 2012 ViewRay launched their MRIdian, MRI guided radiotherapy delivery system initiative, primarily using 3 high-activity Cobalt-60 sources located in three gantry-mounted, rotating heads. Obviously, the physical source size encumbers the beam with some penumbral effects and so this is not ideal for certain small tumours and so in 2016 they announced a 6MV Linac based product with some form of field upgrade to existing users I believe. The Linac based model supersedes this technology and is now being installed it seems at some UK cancer treatment centres as we speak.
And to end we fast forward to 2035 and a seemingly good news conclusion
When you sit in your new electric car at some stage soon, especially salient as the UK government has banned the sales of all diesel, petrol and hybrid cars from 2035 you are likely to be sitting on a very large battery that contains lots of Cobalt. However, Tesla have now said that they would be able to substantially lower the cost of their cars using an alternative battery technology, as cobalt is the most expensive component in traditional nickel-cobalt-aluminium and nickel-manganese-cobalt batteries. Probably very good news for the African children working in the DRC mines mentioned earlier in this blog!
Duncan Hynd – May 2020