A revolutionary new tool for analyzing and planning radiation treatment for cancer patients will be appearing in hospitals within the next few years. Using their storehouse of knowledge and data on nuclear science and radiation transport, Lawrence Livermore scientists have developed PEREGRINE, a hardware and software system that addresses the problem of radiation therapy dosage using fundamental physics principles.|
Each year, about 100,000 Americans die from cancerous tumors that doctors thought were curable. Using current methods for analyzing radiation, doctors unknowingly leave areas of the tumors untreated. Livermore researchers hope that PEREGRINE will improve the efficacy of radiation therapy by helping doctors to direct the radiation accurately. According to Ralph Patterson, who is leading the project, "The PEREGRINE dose calculation system is the best tool available for accurately predicting radiation dose to tumors."
Members of the PEREGRINE team hold one patent related to PEREGRINE and have filed three others. Livermore has recently selected the NOMOS Corporation as a partner to transfer this unique system from the Laboratory into medical clinics. (See also S&TR, May 1997, PEREGRINE: Improving Radiation Treatment for Cancer.)
How It Works
Why PEREGRINE Matters|
Predictions of radiation dose differ by as much as 30 percent between conventional radiation planning techniques and the Monte Carlo method. Conventional techniques may result in the tumor receiving up to 30 percent more or less radiation than the physician intended. At the same time, healthy tissue may be receiving too much. A comparison of conventional and Monte Carlo prediction methods for a case of breast cancer is shown in the figure above.
The Monte Carlo technique is much more effective than conventional methods because it considers the varying densities in the patient's body-of bone, soft tissue, air passages, and so on. This contrasts with current dose calculation methods that model the body as a virtually homogeneous "bucket of water." Even with a CT scan that provides a three-dimensional electron-density map of the body, inhomogeneities such as bone and airways are ignored or highly simplified. Radiation treatments are calculated using interpolated data from dose measurements made in water. The calculations are also based on various simplifications of the way radiation is produced by the source, how radiation travels through the body, and how much energy is deposited.
Some tumors are particularly difficult to treat with radiation because of their proximity to vital organs, the abundance of different tissue types in the area, and the differences in their susceptibility to radiation. Cancers of the head, neck, lungs, and reproductive organs are examples. Too small a dose to the tumor can result in recurrence of the cancer, while too large a dose to healthy tissue can cause complications or even death. Because of the inaccurate dose provided by today's calculations, doctors trying to avoid damage to healthy tissue sometimes undertreat cancerous tissue.
PEREGRINE meets all of these clinical challenges. It can more exactly model the radiation beam delivery system being used for each treatment, accurately model the buildup of dose at the skin surface, and explicitly account for inhomogeneities in the body such as air, muscle, bone, and lung that are identified on the patient's CT scan.
Key Words: cancer treatment, Monte Carlo calculations, PEREGRINE, radiation dose, radiation treatment planning.
For further information contact Ralph Patterson (925) 423-6273 (email@example.com) or the PEREGRINE Web site http://www-phys.llnl.gov/peregrine/.