INTENSITY MODULATED RADIATION THERAPY ( IMRT )
A major advance in radiation therapy is offering certain cancer patients new hope in controlling their cancer, with fewer side effects.

Intensity Modulated Radiation Therapy (IMRT), now being used at Saint Joseph's Hospital in Marshfield, involves varying the intensity of the radiation being used as therapy for cancer. It is a new form of radiation therapy that uses computer-generated images to plan and then deliver more tightly focused radiation beams to cancerous tumors than is possible with conventional radiotherapy.

Saint Joseph's Hospital is the only medical facility in north central Wisconsin now offering the treatment, which was recently approved by the Federal Drug Administration.

"IMRT is the most precise form of radiation therapy available and has the potential of being the biggest advance in radiation therapy since the linear accelerator was developed years ago," said Dr. Warren Olds, Marshfield Clinic Radiation Oncologist on staff at Saint Joseph's hospital. "With this capability, we can deliver a precise radiation dose that conforms to the shape of the tumor, while significantly reducing the amount of radiation to the surrounding health tissues. So, the technique can increase the rate of tumor control while significantly reducing side effects."

The technique can be used for any cancer, but is especially beneficial in head and neck cancers where surgery is not possible, tumors involving the spinal cord and certain cancers in children.

"It allows us to treat tumors considered untreatable in the past due to the proximity of vital organs and structures," said Dr. Olds. "For example, in treating head and neck tumors, IMRT enables the radiation to be delivered in a way that minimizes the exposure to the spinal cord, optic nerves, eyes, salivary glands and other important structures."

The treatment takes no longer than a traditional radiation therapy session, and is done using the existing linear accelerator, which is specially equipped with a multileaf collimator that shapes and delivers the radiation beams according to a specified treatment plan.

Because IMRT uses multiple beams coming from different angles that are precisely conformed to the shape of the tumor, the planning process is done by computer, using an inverse process.

"In conventional radiation therapy, we use a 'forward planning' process, where beam arrangements are tested repeatedly, until a satisfactory dose distribution is produced," said David Loshek, PhD, Radiation Oncology Physicist. "With IMRT, the physician enters the desired radiation beam dose and information about the tumor size, shape and location in the body. Dose-limits to normal organs that we want to protect also are entered. Then, the computer 'back-calculates' to develop an optimal treatment plan to conform to those parameters. A computer also adjusts the intensity of the radiation beams across the field, depending on whether the tumor or normal tissue lies in the beam path."

Because Saint Joseph's Hospital has had the IMRT equipment for nearly a year and been able to test it, patients could be treated right after FDA approval.

"The IMRT is a quantum leap in radiation oncology," said Dr. Olds. "Anything we could treat 10 years ago we can treat better now, and we can treat some cancers that were previously untreatable. It's a key breakthrough in the fight against cancer."