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Fox Chase Cancer Center Study Defines Complexities of New Modality in Radiotherapy of the Lung

PHILADELPHIA (October 23, 2000) -- As Intensity Modulated Radiation Therapy, or IMRT, emerges in the treatment of cancer, doctors have had little or no data to support accurate treatment planning in inhomogeneous media. At the American Society for Therapeutic Radiology and Oncology Annual Meeting in Boston, Mass., (Oct. 23, 10:55 a.m.) a study from Fox Chase Cancer Center was presented examining the accurate dose delivery using IMRT with complex lung treatments when large heterogeneties (different tissue/bone densities) are involved.

IMRT and Inverse Planning may facilitate dose escalation without increasing the harmful effects of radiation in normal tissue. However, to be effective, dose calculation and optimization must be accurate. Calculating the dose is often difficult in low-density materials like a lung. The high dosage used in complex IMRT exacerbate this problem since the plan of distribution for the dose consists of many small fields. In this study, Raj K. Mitra, M.S., Clinical Medical Physicist in the Department of Radiation Oncology at Fox Chase Cancer Center, measured the dose for small fields in a low-density phantom to allow treatment comparisons.

Dose calculations using current treatment planning technology were performed for thin rectangular fields representative of those used in IMRT. A rectangular block lung phantom consisting of 5 cm of polystyrene, 10 cm of cork and 5 cm of polystyrene was irradiated with two different dosimeters. Additional measurements were also performed in a polystyrene/lung equivalent material phantom.

Study results showed that after comparison, most inverse treatment planning systems may overestimate dose to the lung, especially for fields smaller than 3.0 cm in width. The measurements indicated that the discrepancies could be as high as 12% when treating a tumor with a depth of 5 cm in the lung. The cumulative effect of large penumbra (areas of steep dose gradients at the edges of the radiation field) in lung when using IMRT fields of small width, may magnify the discrepancy between doses estimated by most treatment planning systems and the actual measured doses.

"Significant errors may result in both absolute dose and tumor coverage if dose calculations for treatment of lung using IMRT do not account for these small field effects," explained Mitra. "Inverse treatment planning systems that only rely on relative electron density scaling to account for inhomogeneities may not adequately model the radiation transport in lung because the current planning systems ignore lateral electron transport."

Fox Chase Cancer Center, one of the nation's first comprehensive cancer centers designated by the National Cancer Institute in 1974, conducts basic and clinical research; programs of prevention, detection and treatment of cancer; and community outreach. For more information about Fox Chase activities, visit the Center's web site at

Fox Chase Cancer Center, part of the Temple University Health System, is one of the leading cancer research and treatment centers in the United States. Founded in 1904 in Philadelphia as one of the nation’s first cancer hospitals, Fox Chase was also among the first institutions to be designated a National Cancer Institute Comprehensive Cancer Center in 1974. Fox Chase researchers have won the highest awards in their fields, including two Nobel Prizes. Fox Chase physicians are also routinely recognized in national rankings, and the Center’s nursing program has received the Magnet recognition for excellence four consecutive times. Today, Fox Chase conducts a broad array of nationally competitive basic, translational, and clinical research, with special programs in cancer prevention, detection, survivorship, and community outreach.  For more information, call 1-888-FOX CHASE or (1-888-369-2427).

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