Which Rays are Used for the Treatment of Cancer: Beta or Gamma?

The choice of which rays to use in cancer treatment often depends on the specific requirements of the therapy. While both beta and gamma rays play a significant role in radiotherapy, their usage has evolved over time. Here, we explore the reasons behind the shift from beta and gamma rays to linear accelerators, along with the current applications of these rays in cancer treatment.

The Basics of Beta and Gamma Rays

Both beta and gamma rays are forms of ionizing radiation, meaning they have enough energy to strip electrons from atoms and can create charged particles. Beta rays are high-energy electrons emitted during the radioactive decay of atomic nuclei, while gamma rays are high-energy photons emitted in the same process. Despite their similarities, the methods and advantages of using each in cancer treatment differ.

Historically, external-beam radiotherapy used sources like cobalt-60, which is a gamma emitter. These sources were encased in highly shielded containers, often made from depleted uranium, to ensure remote operation and safety. The development of linear accelerators has revolutionized the field, offering numerous advantages over traditional gamma sources.

The Advantages of Linear Accelerators

Linear accelerators generate a beam of high-energy photons, which are effectively X-rays. This method has several advantages over traditional gamma sources:

Higher Penetration: The photons from linear accelerators can have higher energy, making them more penetrating than gamma rays. For a given dose to the target area, the dose to the skin and other tissues is less with a linear accelerator than with gamma rays.Sharper Beams: Due to the limitations of gamma sources' minimum size, the beam edges are much sharper with linear accelerators. This allows for precise shaping of the beam using a multi-leaf collimator, enabling advanced techniques such as intensity-modulated radiotherapy (IMRT).No Radioactive Source Changing: Linear accelerators do not require physical radioactive sources, which need to be changed regularly as they decay. This eliminates the need for transporting and disposing of dangerous material.

Besides generating photons, linear accelerators can also produce electron beams, which are less penetrating and suitable for treating the skin and superficial tissues.

Brachytherapy and Unsealed Sources

While external-beam radiotherapy has largely shifted to linear accelerators, other types of radiotherapy continue to use different methods.

Brachytherapy: In brachytherapy, radioactive sources are placed inside the patient, either temporarily (high dose-rate brachytherapy) or permanently (low dose-rate brachytherapy). Many of the isotopes used in brachytherapy are gamma emitters, but some primary beta emitters are also used.

Unsealed Sources: These sources involve injecting radioactive material directly into the patient's bloodstream, targeting cells within tumors. Examples include radiopharmaceuticals that are actively taken up by tumor cells. These materials are mostly gamma emitters but can include beta emitters.

Alternative Radiations in Cancer Treatment

The field of cancer treatment is continually evolving, with new radiation types being explored and utilized. Here are a few alternatives:

Photons for Precise Dosage: Photons are ideal for treating sites such as the retina of the eye. However, they require the use of cyclotrons, which are not widely available.Neutrons and Whole Atomic Nuclei: These are used in experimental treatment centers, primarily in the US, offering neutron therapy. While powerful, they can cause significant damage to non-cancerous cells due to the high density of ionizations.

The biological effect of neutrons and heavy charged particles is less dependent on the presence of oxygen and the number of treatment fractions, but this comes at the cost of more extensive damage to non-cancerous cells.

The Future of Cancer Treatment

As technology continues to advance, the field of radiotherapy and cancer treatment is likely to see further innovations. Linear accelerators and their advanced features continue to dominate external-beam radiotherapy, but the exploration of alternative radiation types and precision techniques suggests a promising future for personalized and effective cancer treatment.