Therapeutic use of gamma-rays

Therapeutic use of gamma rays

1.	Definition: Gamma radiation is a highly energetic electromagnetic radiation which does not have a deviation in the magnetic field. It appears often with alpha- and beta-radiation. Gamma rays are the same type of ionizing radiation like x-rays but differ in their origin.

γ-radiation originates from “Bremsstrahlung” and transitions in the atomic nucleus (γ-decay): Nucleons (protons, neutrons) go from an energetically higher state in an energetically deeper state. The energy is emitted in form of γ quanta (also known as photons with an energy level > 10-100 keV). It has its smallest wavelength between 10-14m 10-11 and a higher frequency between 1019 and 1022Hz. Due to that, it is the most energetic wave in the electromagnetic spectrum.

Gamma photons consist of electrical neutral particle radiation. Compared to alpha and beta radiation, gamma radiation hast he highest penetration power, even a thick sheet of a dense material such as lead will not block them completely. It has a nearly endless range in air and travels with the speed of light (3x108m/s).

http://www.arpansa.gov.au/images/basics/all_pen.jpg

The picture shows you that Gamma-ray photons have the highest energy in the Electro magnetic radiation spectrum and their waves have the shortest wavelength.

2.	Use and importance in clinical medicine

•	Gamma rays are mostly used in the radiotherapy/ radiooncology to treat cancer. it helps to spot tumors, stenosis, haemorrhage, pulmonary embolism and sterilize equipment.

•	Gamma rays can kill living cells and damage malignant tumor. The Gamma radiation intensitiy decreases exponentially with the depth of penetration. They damage the cancerous cells´DNA, causing them to die or reproduce more slowly.

•	It is mostly used when when the primary tumor has been removed surgically but the oncologist believes that some clusters of tumor cells may remain in the vicinity of the surgical site, when the tumor is detected in early stage of its growth or when low-dose radiotherapy is more harmful to tumor cells than to surrounding tissues, such as in certain skin cancers

http://wiki.hicksvilleschools.org/groups/hsphysicalscience/wiki/c1aed/images/70095.gif

The image represents the technique called Radiotherapy to treat Gamma Rays. They do this by targeting the cancer cells with a beam of radiation then rotating the beam like it is shown in the picture

http://photoimmune.org/wp-content/uploads/2013/04/radiotherapy.jpg

3.

•	Some advantages are: The radiation is pointed at a particular part of the body and in the most cases it does not destroy the surrounding parts. Normal cells in the radiotherapy area may also be damaged but they can usually repair themselves.

•	Some disadvantages are: Gamma rays can interact with the cells in your body,they could damage the body and being the reason for cell death of normal cells. Another result of the use of gamma rays could be an abnormal mitosis, implies a change of DNA, which leads to genetic damage and to DNA mutations in other cells that survive the radiation. This may lead to the development of a second cancer.

•	Gamma rays can pass through medical equipment which is sterilizing the equipment while inactivate viruses and kill bacteria. As the source for gamma rays the radioisotope Colbalt-60 is used.

•	Another use of gamma rays is to do functional imaging. A small amount of radioactivity is administered usually through intra-veinous injection. The radioactive chemical is chosen so that e.g. it is preferentially up taken by cancer cells. Then, a special device named a gamma-camera detects the radioactivity stemming from the body, creates images and allows the physician to locate the cancer cells. The radiographer puts a detector around the body to detect any gamma rays or beta particles that pass out of the patient's body Radioisotopes with short half-lives are chosen to make sure that the tracer does not stay radioactive in the body for long periods

•	How gamma rays work: Gamma rays can create charged particles and free radicals. In cells, the water can be ionized to form free radicals (H+) and (OH-). The free radicals made inside a cell's nucleus can cause damage to the cell's components and breaks in the DNA structure. The cell cannot longer reproduce and the result is cell death.

•	Differentiation Gamma- to X-Rays: The main point of differentiation is, that X rays are emitted by the electrons outside the nucleus and gamma rays are emitted by the nucleus itself. Gamma rays have a smaller wavelength and have an ability to penetrate through nearly all gaps. That is the reason why conventional x-rays of soft tissues often do not produce images that enable accurate diagnosis. Doctors may use specialized gamma-ray scanning equipment to produce a high-quality diagnostic image. But give attention, Gamma rays are more harmful to human body than X-rays, that´s why X rays are used in hospitals for CT and taking X-Rays.

•	Ethical issues: In addition to the many positive characteristics of gamma rays in the medical treatments and possibilities of diagnostic, there are some things that have to be observed in dealing with gamma radiation. Whoever comes into contact with gamma radiation, must be very careful. Not only the patient is exposed to the gamma radiation, which can even promote the formation of cancer cells, but also the medical employees themselves. For this reason, a sufficient self-protection for radiation is very important and that you get trained adequate on dealing with medical equipment using gamma radiation. As a doctor you should also ask yourself the question if it is really necessary of exposing a patient to gamma radiation or not. Otherwise you could probably harm your patient.

4.	Conclusion The primary goal of treatment planning is to precisely calculate the radiation dose to the tumor in order to improve the outcome and reduce toxicity. The future of imaging in radiation therapy treatment planning is promising, and other advances will contribute to better target definition. Higher resolution imaging will be developed for specializing the tumor in an improved way, like higher definition PET-CT scanners and high magnetic field MR would have the ability to improve the visualization of tumors even to the level of microscopic disease extension.

2nd faculty of Charles University, Prague

Biophysics

Gianluca Beckenhaub, Laura Schlicht

Sources:

D. Vordermark, “Ten years of progress in radiation oncology,” BMC Cancer, vol. 11, article 503, 2011.

http://agni.phys.iit.edu/~vpa/medical%20applications.htm

http://www.cancer.org/acs/groups/cid/documents/webcontent/acspc-038756-pdf.pdf

Erste Hilfe- Chemie und Physik für Mediziner 3. Auflage, Springer Verlag ISBN:978-3-662-44110-7