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Radiosensitizer

Radiosensitizer or radio-enhancer is a drug that makes cancer cells more vulnerable to radiation therapy. It enhances the effectiveness of radiation therapy by maximizing tumor cell killing while minimizing irradiating the normal tissues.

Factors to consider when choosing a radiosensitizer

  • Location of the tumor
  • Size of the tumor
  • Types of drugs being administererd
  • Dosage of the drugs and radiation

Example of Radio sensitizing agents

  • Carbogen: Carbogen is a mixture of carbondioxide and oxygen. Its original mixture was 95% oxygen and 5% carbondioxide. Inhalation of carbogen improves tumor oxygenation increasing the effectiveness of radiation therapy.
  • Hyperbaric Oxygen: Hyperbaric Oxygen is used in several cases, such as, healing of circulatory problems, non-healing wounds, strokes and small tumors. It works by providing adequate oxygen to the affected areas through inhalation of 100% oxygen. The increased oxygen, enhances the ability of white blood cells to kill bacteria and to allow growth of new cells, enhancing body’s natural healing.
  • Nicotinamide: Nicotinamide is a skin-restoring agent with the ability to improve weakened skin surface, uneven skin tone, enlarged pores and dullness. It was designed to overcome chronic hypoxia caused by inability of oxygen to diffuse further than 100µm through the respiring tissue or blockage of blood vessels.
  • Hypoxic Cell Cytotoxic Agents: This is a new drug of treating cancer. It was designed to kill the hypoxic cells (solid tumors), which are resistant to both radiotherapy and chemotherapy, by overcoming their resistance.
  • Hyperthermia: Hyperthermia is used in the treatment of radioresistant tumors by enhancing cell killing.

FILM PROCESSING

  • Port film

Port film is an X-ray taken at the beginning of a radiation treatment and once a week during the treatment to ensure proper radiation positioning or proper alignment of the patient with the machine. Proper positioning maximizes tumor killing while minimizing the dose distribution to the normal tissues. Port films keep track of any changes in shape, size and location of the tumor. This is because during the treatment the tumor shrinks, reducing in size and changing in shape.

Limitations of port film

  • Poor quality due to high energy portal film imaging.
  • Poor contrast due to predominance of Compton scattering at mega voltage energies.
  • Blurred images due to patient’s movement or large source or size of the focal point.
  • Image degradation due to scattered photons and secondary electrons.

Radiographic film

Radiographic film is a thin, transparent, blue-tinted base coated on both sides with radiation-sensitive emulsions of silver bromide or silver chloride, silver halide and silver iodide crystals that are suspended in a gelatinous component. The process of producing images on an opaque object on photography film by means of radiation is called Radiographic film processing.

When gamma rays, x-rays or light strike the crystals in the emulsion, some of the Br- ions are liberated and captured by the Ag+ ions. The resultant image on the radiograph will not be so clear hence referred as a “latent (hidden) image”. This is because the change in the grains is too small to be detectable by the ordinary physical methods but the exposed grains are now more sensitive to reduction process when exposed to the developer. The process results in the formation of black, metallic silver and which forms an image.

Factors to consider when choosing a film and developing a radiographic technique:

  • Type of radiation to be used, whether x-rays or gamma rays.
  • Composition, shape, size, weight and location of the area to be examined.
  • Voltage of the x-ray equipment or intensity of the gamma radiation.
  • Relative importance of high radiographic technique.
  • Radiographic film should always be handled carefully to avoid physical strains, finger marks and dirt.

 References:

  1. Medical Dictionary. 2018. Radiographic film.
  2. NDT/NDE Resource Center. Radiography. Retrieved from www.nde-ed.org on 2018/12/16.
  3. P. Stephen, D. Paul. September 2017. Understanding Radiation Therapy Port Films. Retrieved from www.verywellhealth.com on 2018/12/17.
  4. Wikipedia. 2018. Radiosensitizer. 

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