Radioactivity boasts benefits in medicine and beyond
Image credit: Dave Gutteridge, courtesy of UCLH
Radiation therapy sounds like an oxymoron, but carefully managed doses of radiation can treat cancer and some chronic conditions. It is also an asset in feeding the world and fighting crime.
Radiation is a double-edged sword for healthcare. The high-energy waves can be used to examine bones in X-rays and destroy tumours, but the same high-energy rays can be destructive, burning skin and damaging internal organs without any outward sign.
X-rays are a form of electromagnetic radiation, similar to but more intense than infrared, ultraviolet or microwaves. Radiation therapy uses X-rays and gamma rays delivered in a beam of high-energy light by an external source. Today, around 50 per cent of cancer patients benefit from radiation therapy in the treatment and management of their disease.
The rays actively divide cells in DNA and also oxidise water to make free radicals, which diffuse to the DNA. Splitting a double strand in the DNA in a tumour cell will kill it.
There are different modes of radiotherapy, from low-energy (kV) to high-energy (MV) X-rays for deeper penetration, to electron beam and cobalt therapy, using gamma rays. There is also brachytherapy, which uses radioactive sources in localised tumour tissues and at varying energy levels.
The nature of radiation therapy means that it can also affect healthy tissue around the tumour. Making it more precise enables the radiation dose to be increased and to reduce the treatment time.
A process called stereotactic body radiation therapy (SBRT) uses image guidance and 4D CT scanning to establish the precise location of tumours in organs such as the lungs or liver. Traditional radiation therapy uses a larger target area with wider margins around the tumour to accommodate movement.
In SBRT, the patient wears a belt to monitor respiration during the CT scan and the beams can be turned on and off as the tumour moves within the field of interest. Mapping the location of the tumour allows the maximum doses of radiation to be applied from multiple angles and aimed at the most active part of the tumour.
Research at UCLA (University of California Los Angeles) has found that SBRT has a control rate of 90 per cent compared with 30 per cent with traditional radiation therapy in lung cancer patients. It is also used to treat liver cancer. Some patients are cured and do not need surgery but for those who do need a transplant, UCLA reports primary evidence suggesting that patients treated before a transplant have a low rate of recurrence.
Radiation can also be administered internally via brachytherapy. This is when sealed radioactive ‘seeds’ are implanted to deliver radiation at a short distance. They can be placed between tissue and an organ (interstitial), inside a body cavity, for example the windpipe or rectum, or applied on the surface, to treat skin cancer.
Since the 1980s, synthetic radionuclides or radioactive isotopes have been used in these seeds. There is caesium-137, iridium-192, gold-198, which has a half-life of less than three days, and iodine-125, which has a half-life of 60 days. The radioactive seeds are encased in titanium and range from the size of a large sesame seed to a grain of rice (4.5 x 0.8mm is common).
There is also research into using automatic devices that are remote controlled to deliver radiation. Brachytherapy can be combined with radiation delivered by an external beam or as a standalone treatment, depending on the cancer.
Proton beam therapy represents a real advance in how high-energy rays are administered. Locating the precise position of a tumour for conventional radiation therapy allows high-energy rays to be fired directly into it. Although effective on the tumour, healthy tissue between the skin and the tumour is at risk of radiation damage. Rays fired in proton beam therapy peak before suddenly fading away – an effect called the Bragg peak. This minimises damage to surrounding tissue.
To deliver the proton beams, an accelerator increases the speed of protons in a cyclotron to 160,000km per second before directing the beam via electromagnets to a treatment gantry and then through a nozzle positioned against the patient, who is lying still on a robotically controlled table. The nozzle fires at hundreds of tiny spots within the tumour in just 26 seconds. The nozzle can be repositioned to repeat the process to attack the tumour from a different angle.
The therapy is being used for tumours in sensitive areas, such as the brain and spine, allowing high doses on specific areas. To ensure pinpoint accuracy of this intense beam, calibration marks are tattooed on the patient to line up the tumour with the lasers in the proton beam therapy pod. It can take more than 15 minutes to position the patient for less than one minute of treatment. The treatment is administered daily over a period of weeks.
Researchers at Johns Hopkins University School of Medicine in Maryland, USA, have found that treating spinal tumours with a series of doses, rather than a single large one, helps prevent vertebral compression fractures. Radiation and tumours can weaken the bones in the spine, explained Timothy Witham MD, director of the Johns Hopkins Medicine Spinal Fusion Laboratory, pointing out that fractures can complicate or delay recovery.
The researchers administered a single dose of 24 gray (Gy) to one test group of rabbits and delivered three doses of 8Gy each to another group. A control group received no radiation. It was found that the bones in the second group were less impacted and that bone samples receiving a single dose broke more easily than those given the same amount of radiation over separate sessions.
“Based on this study, we can immediately recommend that oncologists use fractioned radiation dosage in their practices and, hopefully, prevent further suffering,” concludes Witham.
Treatment has reached the limit of radiation, so rather than increasing the dose, other research is investigating how to optimise the effects of the radiation. In 2010, a study published in Radiation Research found that gold nanoparticles introduced intravenously around the site of the tumour accumulated in the tumour and interacted with X-ray photons still present from the radiation treatment. Together, these interact with water molecules to produce free radicals which damage the tumour cells. By boosting the effects of radiation, the tumour’s ability to recover and repair was limited without the radiation dose being increased.
When it decays, radium emits radon gas. In the 1930s, mine workers reported that some chronic conditions, such as arthritis, were eased as a result of exposure to radon. It has been claimed that the gas acts on the body’s endocrine system to encourage production of hormones and steroids that help the body heal, though radon is also a known cause of lung cancer.
In the US today, former gold, silver and copper mines in Montana operate as health mines. Visitors sit in or walk the mines for an hour at a time, accumulating a total of 30 hours exposure to radon during their stay. Spas in Austria, Germany and Poland offer radon bathing, water for drinking and therapy tunnels (in caves or former mine areas).
The health benefits of radon exposure are a contentious issue. Visitor testimonials report relief from chronic ailments including asthma, arthritis, carpal tunnel syndrome, fibromyalgia, eczema, and psoriasis. The US Environmental Protection agency, however, says that there is no safe level of radon and that any exposure poses some risk of cancer.
Radiation’s ability to kill bacteria means that fruit can be exposed to beams of radiation. This is called irradiation and is different from contamination by radioactive material. Fruit is typically irradiated using cobalt-60 gamma rays. The radiation destroys any bacteria but will not change the fruit.
Doses of gamma or neutron radiation can also be used to create plant mutations. Crops can be modified to resist disease, tolerate drought or harsh environments, increase yield, or have shorter growing times to increase harvests.
Low doses can make fresh fruit and vegetables, cereals, and root crops resistant to infestation by insects and parasites. Medium doses (1-10kGy) can extend the shelf life of fish, poultry and meat and fleshy produce like strawberries and mushrooms. High doses (10-50kGy) are used for industrial sterilisation and decontamination of meat, poultry, seafood, prepared food and spices.
In addition to being able to grow crops in inhospitable areas, genetically modified crops may require fewer chemicals, such as pesticide and insecticide, during cultivation.
Radiation is also used to control insect populations. The insects are sterilised through irradiation with X-rays or gamma rays and introduced to their natural habitat. One benefit of this sterile insect technique (SIT) is that it does not introduce non-native species into an ecosystem. SIT has been used to eradicate the Mediterranean fruit fly in Mexico, Argentina and Chile and the parasitic screw worm in southern US, Mexico, Central America, and Panama.
Ionising radiation is also used in manufacturing to sterilise materials, components, and packaging. There are two processes typically used. Gamma irradiation can be used for batches of product in a fixed location, or a conveyor belt can transport products into a radiation cell for exposure as they pass through. The other process is high-energy electron irradiation, or beta radiation, from an accelerator. Products are conveyed past a beam of high-energy electrons, which is transmitted back and forth across the conveyor belt.
In the art world, radiation is used to learn more about the creation of artworks and also to unmask forgeries.
X-ray fluorescence (XFR) is a technique to determine the chemical composition of works of art. Subjecting the work to high-energy gamma or X-rays destablises the electrons, which emit radiation. This radiation is different depending on the chemical compound. Analysing the radiation can identify what chemical elements were used in paint. For example, XRF was used to determine where a painting attributed to Leonardo da Vinci had been retouched long after it was originally painted. Da Vinci used lapis lazuli for his blue pigments, and while this was present, there was also cobalt blue, but this artificial pigment was not available during da Vinci’s lifetime.
The Courtauld Institute in London used X-rays to show the progression of some of Edouard Manet’s works for a 1986 exhibition, 'The Hidden Face of Manet'. In his celebrated painting, 'A Bar at the Folies Bergère', X-ray pictures highlight the original position of the central character’s arms. Originally, Manet depicted the barmaid with her arms crossed instead of resting on the bar as they appear in the final painting.
White paint contains lead and is used for flesh tones, so the original positioning of faces as well as arms and legs can be exposed under X-rays. Other metallic pigments are cadium and cobalt (blue) and mercury (vibrant red, vermilion).
Other X-rays show the addition of a cat at the end of a bed in Olympia, and the changing landscape in 'Le Déjeuner sur l’Herbe'.
In a 1921 speech, Marie Curie reflected on her discovery of radium. “No one knew that it would prove useful in hospitals. The work was one of pure science,” she said. She had isolated the chemical element Ra (atomic number 88) in 1902, extracting 0.1g of pure radium chloride from three tonnes of pitchblende ore.
It was found that exposure to skin for two 20-minute periods produced an inflammation which lasted for weeks and was similar to the effects of a long exposure to the X-rays discovered by Wilhelm Röntgen in 1895.
In 1903, Pierre Curie, Marie’s husband and fellow physicist, gave a lecture at London’s Royal Institution describing radium’s flesh-burning ability and suggested it might be used to treat cancer.
Radium salt was initially applied to the skin to treat lesions and basal cell carcinoma (rodent ulcers), which are in the lowest skin layer and linked to exposure to the Sun.
Soon, medics wanted to treat cancer inside the body. John MacLeod developed radium applicators to treat throat cancer.
A glass phial containing radium salt was fixed to the end of flexible tube. The patient had to bite on a rubber part of the tube to keep the phial in place so it could treat the cancer. The tube was adapted as a thin catheter to treat prostate cancer.
Hollow needles containing radium salts were introduced later. These were inserted at different angles around the treatment area to target the cancerous cells.
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