• David I Rosenthal, Mark S Chambers, Clifton D Fuller, Neal C S Rebueno, John Garcia, Merrill S Kies, William H Morrison, K Kian Ang, and Adam S Garden.
• Department of Radiation Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, TX, USA.
• Int. J. Radiat. Oncol. Biol. Phys. 2008 Nov 1; 72 (3): 747-55.

BackgroundIntensity-modulated radiation therapy (IMRT) beams traverse nontarget normal structures not irradiated during three-dimensional conformal RT (3D-CRT) for head and neck cancer (HNC). This study estimates the doses and toxicities to nontarget structures during IMRT.Materials And MethodsOropharyngeal cancer IMRT and 3D-CRT cases were reviewed. Dose-volume histograms (DVH) were used to evaluate radiation dose to the lip, cochlea, brainstem, occipital scalp, and segments of the mandible. Toxicity rates were compared for 3D-CRT, IMRT alone, or IMRT with concurrent cisplatin. Descriptive statistics and exploratory recursive partitioning analysis were used to estimate dose "breakpoints" associated with observed toxicities.ResultsA total of 160 patients were evaluated for toxicity; 60 had detailed DVH evaluation and 15 had 3D-CRT plan comparison. Comparing IMRT with 3D-CRT, there was significant (p 36 Gy, occipital scalp dose >30 Gy, and anterior mandible dose >34 Gy, respectively.ConclusionsDose reduction to specified structures during IMRT implies an increased beam path dose to alternate nontarget structures that may result in clinical toxicities that were uncommon with previous, less conformal approaches. These findings have implications for IMRT treatment planning and research, toxicity assessment, and multidisciplinary patient management.

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