Three-Dimensional Radiation Treatment (3D-CRT)

Three-dimensional conformal radiation therapy, or 3D-CRT, is a complex process performed by an experienced radiologist. The noninvasive treatment involves creating 3-D computer images and delivering highly conformed (focused) radiation on malignant tumors while sparing normal adjacent tissue.

3D-CRT is a type of external beam radiation therapy (EBRT), which is the most common form of radiation treatment used for mesothelioma. Scientists are developing new methods of providing radiotherapy to mesothelioma patients that make irradiating the affected area more precise and lessen the risk of harming healthy tissue.

Conforming the radiation beam to the three-dimensional shape of the tumor precisely targets the tumors while reducing side effects. 3-D conformal radiation therapy is used less often for pleural mesothelioma because intensity-modulated radiation therapy (IMRT) — an advanced form of 3D-CRT — is even safer and more effective.

IMRT combines the precise 3-D targeting of 3D-CRT with a computer-controlled device called a linear accelerator, which changes the speed and strength of the radiation beams in certain areas.

A treatment session of 3D-CRT typically lasts 15 to 30 minutes, although the first appointment — which includes scans and checks — may be longer.

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 such as size, shape and location of the tumor and the organs that surround it.

A radiation oncologist uses this information to create customized beams utilizing other tools, including:

  • Multileaf Collimator: A device attached to the head of the machine. It has rows of platelets that are separate from each other, known as leaves, which 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: These are made of a material such as 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.

3-D Conformal CRT Improves Control

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Radiation’s exact role as part of multimodality 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-CRT 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 an issue with intensity-modulated radiotherapy than it is with the 3-D conformal treatment.

Risks of 3D-CRT

Patient being scanned

Three-dimensional conformal radiotherapy is a complex process that requires an experienced radiologist, especially when treating pleural mesothelioma patients.

Some patients treated with 3D-CRT experience no side effects. When adverse effects do occur, they are generally related to the area of the body being treated.

These side effects are usually not serious and go away within four to six weeks after treatment ends. Medication or changes to your diet can help control potential side effects.

Negative side effects of 3D-CRT include:

  • 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.

You should consult with your oncology team to determine if 3D-CRT is the best form of radiation or if radiation therapy is needed at all. Every mesothelioma case is unique.

A mesothelioma specialist will be able to formulate the best treatment plan based on the location and size of tumors, staging of the cancer and overall health of the patient.

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Karen Selby, RN and Patient Advocate at The Mesothelioma Center

Karen Selby joined Asbestos.com in 2009. She is a registered nurse with a background in oncology and thoracic surgery and was the director of a tissue bank before becoming a Patient Advocate at The Mesothelioma Center. Karen has assisted surgeons with thoracic surgeries such as lung resections, lung transplants, pneumonectomies, pleurectomies and wedge resections. She is also a member of the Academy of Oncology Nurse & Patient Navigators.

Sources
  1. Sutter Health Palo Alto Medical Foundation. (n.d.). Three-Dimensional Conformal Radiotherapy. Retrieved from http://www.pamf.org/radonc/tech/3d.html
  2. American Cancer Society. (2016, February 17). Radiation Therapy for Malignant Mesothelioma. Retrieved from https://www.cancer.org/cancer/malignant-mesothelioma/treating/radiation.html
  3. American Cancer Society. (2017, February 10). External Beam Radiation. Retrieved from https://www.cancer.org/treatment/treatments-and-side-effects/treatment-types/radiation/external-beam-radiation-therapy.html
  4. Stahel, R.A. et al. (2010, May). Malignant pleural mesothelioma: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Retrieved from http://www.esmo.org/Guidelines/Lung-and-Chest-Tumours/Malignant-Pleural-Mesothelioma
  5. Science Daily. (2007, May 10). Targeted, high-energy cancer treatments get a supercomputing boost. Retrieved from https://www.sciencedaily.com/releases/2017/05/170510115320.htm
  6. Claude, L. et al. (2004, May). A prospective study on radiation pneumonitis following conformal radiation therapy in non-small-cell lung cancer: clinical and dosimetric factors analysis. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/15110451
  7. Singh, AK., Lockett, MA, and Bradley, JD. (2003, Feb 1).Predictors of radiation-induced esophageal toxicity in patients with non-small-cell lung cancer treated with three-dimensional conformal radiotherapy. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/12527046

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