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Int J Radiat Oncol Biol Phys. 2014 Jul 1;89(3):626-32. doi: 10.1016/j.ijrobp.2014.03.022.

Comparison of radiation-induced normal lung tissue density changes for patients from multiple institutions receiving conventional or hypofractionated treatments.

Author information

  • 1Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, Colorado. Electronic address:
  • 2Department of Radiation Oncology, University of North Carolina, Chapel Hill, North Carolina.
  • 3Division of Biostatistics and Bioinformatics, University of Maryland Greenbaum Cancer Center, and Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, Maryland.
  • 4Department of Radiation Oncology, VU University Medical Center, Amsterdam, The Netherlands.
  • 5Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, Colorado.
  • 6London Regional Cancer Program, London, Ontario, Canada.



To quantitatively assess changes in computed tomography (CT)-defined normal lung tissue density after conventional and hypofractionated radiation therapy (RT).


The pre-RT and post-RT CT scans from 118 and 111 patients receiving conventional and hypofractionated RT, respectively, at 3 institutions were registered to each other and to the 3-dimensional dose distribution to quantify dose-dependent changes in normal lung tissue density. Dose-response curves (DRC) for groups of patients receiving conventional and hypofractionated RT were generated for each institution, and the frequency of density changes >80 Hounsfield Units (HU) was modeled depending on the fractionation type using a Probit model for different follow-up times.


For the pooled data from all institutions, there were significant differences in the DRC between the conventional and hypofractionated groups; the respective doses resulting in 50% complication risk (TD50) were 62 Gy (95% confidence interval [CI] 57-67) versus 36 Gy (CI 33-39) at <6 months, 48 Gy (CI 46-51) versus 31 Gy (CI 28-33) at 6-12 months, and 47 Gy (CI 45-49) versus 35 Gy (32-37) at >12 months. The corresponding m values (slope of the DRC) were 0.52 (CI 0.46-0.59) versus 0.31 (CI 0.28-0.34) at <6 months, 0.46 (CI 0.42-0.51) versus 0.30 (CI 0.26-0.34) at 6-12 months, and 0.45 (CI 0.42-0.50) versus 0.31 (CI 0.27-0.35) at >12 months (P<.05 for all comparisons).


Compared with conventional fractionation, hypofractionation has a lower TD50 and m value, both suggesting an increased degree of normal tissue density sensitivity with hypofractionation.

Copyright © 2014 Elsevier Inc. All rights reserved.

[PubMed - indexed for MEDLINE]
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