Three-Dimensional Radiation Treatment (3D-CRT)

Providing radiation treatment using traditional external beam radiotherapy makes it necessary for the radiation oncologist to look at images from numerous CT scans, MRIs, and nuclear imaging scans. They are viewed in sections, and these sections are pieced together to form a treatment plan.

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This creates an approximation of the target and causes risk of irradiating normal tissue that can become damaged. To prevent normal tissue from becoming injured, the dosage administered may be lower than needed to destroy the cancer cells.

New methods of providing radiotherapy to mesothelioma patients are being developed that make irradiating the affected area more precise and lessen the risk of harming healthy tissue. One of these is called Three-Dimensional Conformal Radiation Treatment or 3D-CRT.

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3D-CRT Uses Other Scan Information

Two-dimensional images gathered from a patient's CT Scans, MRIs and PET scans are fed into a dome-shaped projector that rotates. This dome, which is plugged into a computer, projects the images as three-dimensional holograms. These are not pictorial images like the ones seen on other types of tests, but rather light images that indicate characteristics like size, shape and location of the tumor and the organs that surround it.

A radiation oncologist uses this information to create customized beams using other tools such as:

  • Multi-leaf collimator, a device attached to the head of the machine. It has rows of platelets that are separate from each other, known as leaves that can be manipulated to either allow or block beams from penetrating the target. This creates the initial shape and size of the portal through which the beams will be emitted.
  • Custom-fabricated, field-shaping blocks are made of a material like lead that stops the flow of light. They are placed around the portal to further conform the radiation beams to the shape of the tumor.

3D Conformal CRT Improves Control

Brain Scan

Radiation's exact role as part of multi-modality treatment of mesothelioma is still being evaluated. A part of that ongoing investigation is experimentation with how to deliver necessary high doses of radiation to the side of the thorax with the diseased lung without damaging normal tissue (especially within the lung).

Research shows that after an extrapleural pneumonectomy, it is possible to deliver doses of greater than 45 Gy (gray) with 3D conformal radiotherapy without serious risk. A gray is a unit that measures the amount of energy absorbed by a kilogram (approximately two pounds) of body tissue.

However, a radiation oncologist must exercise caution in exposing the opposite lung to low-dose radiation. This is more of a proble>m with intensity-modulated radiotherapy than it is with the 3D conformal.

Risks of 3D CRT

Although there are a number of benefits to 3D CRT, three are also some negative side effects. Among them are:

  • Radiation pneumonitis: An inflammation of the lungs that typically starts within two to three months of the start of the radiotherapy. Its symptoms can include a dry cough, shortness of breath brought on by exertion and low-grade fever. Although this is usually temporary, it can lead to permanent scarring of the lungs.

  • Esophagitis: Occurs when the esophagus (the food tube that runs from the throat to the stomach) becomes inflamed. This condition typically starts about two weeks after the beginning of treatment and usually disappears about two to three weeks after treatment is completed.

  • Mucositis: A condition where the lining of the mouth, throat and gums (called the oral mucosa) become inflamed. It is accompanied by dry mouth, thick saliva, sores and difficulty chewing or swallowing. It is also a temporary condition that ends within a few weeks of the completion of treatment.

Additional Resources

  1. Singh AK, Lockett MA, Bradley JD. "Predictors of radiation-induced esophageal toxicity in patients with non-small-cell lung cancer treated with three-dimensional conformal radiotherapy." (Feb. 1, 2003). Int J Radiat Oncol Biol Phys.55(2):337-41. Retrieved from: http://www.ncbi.nlm.nih.gov/pubmed/12527046
  2. Claude L, Pérol D, Ginestet C, Falchero L, Arpin D, Vincent M, Martel I, Hominal S, Cordier JF, Carrie C. "A prospective study on radiation pneumonitis following conformal radiation therapy in non-small-cell lung cancer: clinical and dosimetric factors analysis." (May 7, 2004).
  3. Radiother Oncol.1(2):175-81. Retrieved from: http://www.ncbi.nlm.nih.gov/pubmed/15110451
  4. R. A. Stahel, W. Weder, Y. Lievens, E. Felip. On behalf of the ESMO Guidelines Working Group. "Malignant pleural mesothelioma: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up." Annals of Oncology 21 (Supplement 5). Retrieved from: http://annonc.oxfordjournals.org/content/21/suppl_5/v126.full.pdf+html
  5. Targeting Cancer in 3D: Medical Physicists Improve Vision for Radiation Therapy. Science Daily. (Jan. 1, 2007). Retrieved from: http://www.sciencedaily.com/videos/2007/0108-targeting_cancer_in_3d.htm
  6. Radiation Therapy Services. TrailBlazer Health Enterprises. (August 2011). Centers for Medicare and Medicaid Services. Retrieved from: http://www.trailblazerhealth.com/Publications/Job%20Aid/RadiationTherapyServices.pdf

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