Intensity-modulated radiation therapy (IMRT) is high-precision radiotherapy that utilizes today's technology to deliver therapeutic doses of radiation. The treatment uses computer-controlled x-ray accelerators to deliver precise radiation doses to a malignant tumor or specific areas within the tumor. Historically the use of radiation therapy, while effective with many types of tumors, has been damaging to surrounding healthy tissues because there has not been a method for focusing the radiation sufficiently. IMRT minimizes damage to surrounding tissue through precision focus and through the use of lower levels of radiation.
IMRT is image driven. Computerized Tomography (CT) scans provide a three dimensional image of the tumor and surrounding tissues. Treatment can be planned using these computed tomography (CT) images that takes into consideration the density of the tumor, its sources of nourishment its limits where adjacent to healthy tissue, and the variety of tissue depth in different areas of the tumor which in turn dictates the intensity of the radiation. The modulated X-ray beams are shaped, in a fashion, to match the dimensions of the tumor.
IMRT Technology
This form of treatment requires a linear accelerator for generation of radiation. These machines can be utilized with great precision, generating what is referred to as "conformal radiation" because it conforms to the shape of the tumor. In instances where a tumor adjoins critical organs or tissues, such as with peritoneal mesothelioma, conformal radiation can be applied where standard radiation treatment cannot. IMRT uses higher doses of radiation than conventional radiotherapy, but the technology design results in lower exposure for adjoining health tissues. For that reason multiple treatment sessions can be scheduled without causing major occurrences of unpleasant side effects.
Planning a treatment session for IMRT can take a couple of days, although newer versions of the equipment have been developed that accelerate the process. The analysis of 3D tomograms and programming the IMRT machinery to deliver multiple radiation waves of varying strengths for varying periods to affected areas requires careful, detailed planning. It is not point and shoot technology like the traditional radiotherapy machines utilize. The machine itself is a "medical linear accelerator" that can be nine feet tall and fifteen feet long. Both the patient and the linear accelerator can be moved, delivering radiation to the focal point based on programmed sequencing.
IMRT for Mesothelioma Treatment
IMRT is often scheduled five days a week for a fifteen minute session. This approach is very different from the traditional massive dose delivered with conventional radiotherapy, conducted once a week or once every two weeks. The precise delivery minimizes side effects and makes a more consistent treatment program possible. Treatment is generally a six or seven week cycle. Currently, IMRT is being used most extensively to treat cancers of the prostate, head and neck, and central nervous system. It is being used for the radiotherapy portion of mesothelioma treatment in some facilities, notably the MD Anderson Cancer Center in Houston, which has an active mesothelioma research and treatment program.
The technology is also being utilized to provide postoperative treatment for malignant mesothelioma patients that have had a pleurectomy or an extrapleural pneumonectomy, surgery to remove the pleura or the pleura and a lung, respectively. The goal in an early test was to prevent reoccurrence of malignant mesothelioma and at one year, the results were very successful. The researchers caution that an early test such as this one does not take into account the systemic development of metastasized cancer, but the technology has shown to be very effective with localized pleural mesothelioma.
Sources:
- IMRT, International RadioSurgery Association, http://www.irsa.org/imrt.html
- Linear Accelerator, RadiologyInfo.org, American College of Radiology, http://www.radiologyinfo.org/en/info.cfm?pg=linac
- IMRT Patient Information, OncoLink.org, University of Pennsylvania Abramson Cancer Center, http://www.oncolink.org/treatment/article.cfm?c=5&s=33&id=179
- Early Local Control…Postoperative IMRT, The Cancer Journal, Vol. 9 Issue 6, Ahamad et al, http://journals.lww.com/journalppo/Abstract/2003/11000/Promising_Early_Local_Control_of_Malignant_Pleural.8.aspx
