IMAT MORE ACCURATE THAN IMRT

July 27, 2010 (Philadelphia, Pennsylvania) — Children with brain cancer who undergo chemotherapy may benefit from a technique known as intensity-modulated arc therapy (IMAT).

New research findings reported here at the American Association of Physicists in Medicine 52nd Annual Meeting by Chris Beltran, PhD, from St. Jude's Children's Research Hospital in Memphis, Tennessee, show that IMAT may effectively irradiate pediatric brain tumors while reducing exposure to surrounding tissue compared with the more conventional intensity-modulated radiation therapy (IMRT).

Dr. Beltran told Medscape Medical News, "We are always looking to minimize dosage to normal tissue. Any technology that can do that should be taken into account and evaluated." The study included 9 patients (mean age, 9.6 years) who were diagnosed with posterior fossa tumors and had been treated with IMRT within the past year.

"[The posterior fossa] is such a busy area, and it is very difficult to give an adequate dosage without hurting vital structures," Franklin Epstein, MD, chief of the Division of Neurosurgery at Audie L. Murphy Memorial Hospital in San Antonio, Texas, noted during an interview with Medscape Medical News in response to Dr. Beltran's findings. Dr. Epstein was not affiliated with the study.

Radiation therapy is designed to deliver full radiation to the target while minimizing exposure to the cochlea and other important surrounding tissues. However, Dr. Beltran pointed out that radiation of the whole brain and temporal lobes can result in hearing and cognitive damage. This led the investigators to test the efficacy of IMAT as an alternative treatment approach, subsequent to the initial course of IMRT.

The investigators replanned the children's therapy using 5 different approaches: 8 field non-coplanar IMRT, single coplanar IMAT, double coplanar IMAT, single non-coplanar IMAT, and double non-coplanar IMAT. Each of the therapy plans held the dose to 95% of the planning target volume constant.

The plans were then compared based on conformality index, monitor units, and dose to surrounding normal tissue.

In the case of double non-coplanar IMAT, the excess radiation dose (V50 and VD50) to both cochleae and temporal lobes was significantly decreased (P < .01) relative to IMRT. In contrast, the body V5 and monitor units were increased (P < .01). The double non-coplanar IMAT also resulted in improved conformality index (P = .05) relative to IMRT.

Dr. Beltran said the findings indicate that the double non-coplanar IMAT may be able to improve treatment of pediatric posterior fossa tumors compared with the standard non-coplanar IMRT.

The new IMAT technology appears to be able to better target the radiation and minimize adverse effects, Dr. Epstein observed. He said that the IMAT technique is "just a variation on a variation, and it could go right to clinical study."

The study did not receive commercial support. Dr. Beltran and Dr. Epstein have disclosed no relevant financial relationships.

American Association of Physicists in Medicine 52nd Annual Meeting: Abstract 12612. Presented July 18, 2010.