Medicine

1. In diagnostic imaging, radioactive tracers are used in techniques such as PET (positron emission tomography) and SPECT (single photon emission computed tomography) scans, allowing clinicians to visualize organs and tissues in detail, track physiological processes, and detect diseases at early stages. Similarly in radionuclide therapy or radioisotope therapy, radioactive isotopes are used as targeted treatments for various cancers and certain other medical conditions. Often, radioisotopes are combined with molecules that specifically target cancer cells (like peptides or antibodies), where isotopes like lutetium-177 (Lu-177) are attached to molecules targeting specific receptors on neuroendocrine tumor cells. Alternatively, radioisotopes can be bound to antibodies targeting particular cancer cells, such as in certain lymphomas.

2. Radiotherapy, which uses ionizing radiation to treat cancer, includes two primary forms: external beam radiation therapy and brachytherapy. In external beam radiation therapy, high-energy radiation from an external source, such as Cobalt-60 (Co-60) or a linear accelerator, is precisely directed at the tumor from outside the body. This method is designed to maximize radiation exposure to cancer cells while minimizing harm to nearby healthy tissue. Brachytherapy, on the other hand, involves placing radioactive sources directly inside or very close to the tumor, delivering a high dose of radiation directly to the cancer cells. This localized approach is often used in treating cancers of the prostate, cervix, and breast, providing targeted treatment with reduced exposure to surrounding tissues.

3. Radiation sterilization plays a crucial role in general medicine by sterilising medical instruments and supplies, such as syringes, gloves, and surgical tools. This process uses gamma rays or electron beams to eradicate bacteria, viruses, and other pathogens, ensuring the sterility and safety of equipment used in medical procedures. 

These applications illustrate how radioactivity has transformed medicine, improving diagnostic capabilities, advancing cancer treatment options, and enhancing patient safety. All of these require transport of the radioactive materials, either to the site of the Sterilisation equipment or to the hospital for direct lifesaving use for patients.

Meta-stable Technetium-99m (Tc-99m) is used as a radioactive tracer and can be detected in the body by medical equipment (gamma cameras). It is well suited to the role, because it emits readily detectable gamma rays  and its half-life is 6 hours (meaning half of it decays in 6 hours and 93.7% of it decays in 24 hours). The relatively short half-life of the isotope allows rapid diagnostic procedures while keeping the total patient radiation exposure low. As a result, TC-99m is the most commonly used radioactive tracer and is used in around 30 million diagnostic procedures worldwide every year [1].

Several injectable radioisotopes are used in cancer treatment, particularly for targeting and destroying cancer cells with minimal impact on healthy tissues. These radioisotopes emit radiation that can be precisely directed at cancer cells, making them effective in treating cancers that have spread or are challenging to target with external beam radiation. Some commonly used injectable radioisotopes include:

Radium-223 (Ra-223): This alpha-emitting radioisotope is used to treat prostate cancer, specifically targeting cancer that has spread to the bones. Ra-223 mimics calcium and is taken up by bones, where it emits high-energy alpha particles that destroy nearby cancer cells. It has a half-life of 11.4 days.

Iodine-131 (I-131): Iodine-131 is widely used to treat thyroid cancer and certain types of hyperthyroidism. Because iodine is naturally absorbed by the thyroid gland, I-131 effectively targets thyroid tissue, delivering beta radiation that destroys cancerous cells in the thyroid. It has a half-life of 8 days. Figure 4 shows a vial of I-131 being removed from the shielding pot with the outer packaging behind.

Lutetium-177 (Lu-177): Lutetium-177 is used in peptide receptor radionuclide therapy (PRRT) to treat certain neuroendocrine tumors and to treat prostrate cancer. Lu-177 is combined with a targeting molecule, which binds to receptors on the cancer cells, allowing targeted radiation delivery to the tumors. It has a half-life of 6.7 days.

These injectable radioisotopes provide valuable options for cancer treatment, especially for patients with metastatic or difficult-to-treat cancers. By directly targeting cancerous tissues, they can deliver therapeutic doses of radiation while minimizing side effects and damage to surrounding healthy tissue.

Transport of these materials is typically carried out in small quantities in Excepted packages or Type A packages which are transported on aeroplanes or by road. Fast transport from the point of production to the point of use is essential as the materials have a short half-life.  This means that any delays in transport can result in fewer patient doses being available when the radioisotope is used, or in the worst case, the material may not be usable at all. For example, TC-99m is transported in a package such as the one shown in Figure 6 as Molybdenum-99 (Mo-99) which produces Tc-99m as it decays.  Tc-99m is extracted from the Mo-99 using a Technetium Generator (which may be designed to also act as the transport package). It is transported in this form as Mo-99 has a longer half-life of 66 hours than Tc-99m which has a half life of just 6 hours. However a delay of just 24 hours will still result in the decay of a quarter of the Mo-99 leading to a the loss of a quarter of the patient doses of Tc-99m. It is therefore vital that the transport is carried out safely and promptly. In all cases, the transport is undertaken in accordance with the regulations of the countries concerned which are based on the IAEA’s Regulations for the Safe Transport of Radioactive Material [3].

The design and performance standards for packages used for the transport of radioactive material, including nuclear fuel cycle material, are defined in the International Atomic Energy Agency (IAEA) Regulations for the Safe Transport of Radioactive Material [3].  The regulations have been in place since the 1960s and are regularly reviewed and updated.  This has resulted in a history of over 60 years of safe transport or radioactive materials.  The regulations take a graded approach (Figure 7) to safety with the level of protection increasing with the radioactive hazard. For low hazard materials, such as a single dose of a radiopharmaceutical for injection into a patient, the excepted package may be simply a robust cardboard box with absorbent material to soak up any spillage.  For larger quantities of radiopharmaceuticals, a more robust Type A package may be used. For higher activity Co-60 sources used in sterilisation equipment, a Type B package would be required with appropriate shielding to protect the public and the environment.  In addition, the design of the package must ensure that it meets the severe accident conditions defined in the regulations covering impact, fire and immersion in water.

Nuclear medicine has an ever increasing role in modern medicine. Co-60 is used for sterilisation of singe use medical products and medical radioisotopes are crucial in modern healthcare for diagnosis, treatment, and research.

Many of the radioisotopes have short half-lives so must be transported to the clinics promptly and regularly to allow patents to be treated. Delays can lead to a significnt loss of patient doses.

Transport of these vital lifesaving materials is carried out safely in accordance with the international transport regulations [3] to treat cancer and other conditions in millions of patients around the world every year.

1. OECD/NEA (2019), The Supply of Medical Isotopes: An Economic Diagnosis and Possible Solutions, OECD
   Publishing, Paris, https://doi.org/10.1787/9b326195-en.
2. https://world-nuclear.org/information-library/nuclear-fuel-cycle/nuclear-power-reactors/small-nuclear-power-reactors
3. https://www.iaea.org/publications/12288/regulations-for-the-safe-transport-of-radioactive-material
4. https://www.iaea.org/publications/documents/conventions/convention-physical-protection-nuclear-material-and-its-amendment