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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

Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, Colorado. Electronic address:
Department of Radiation Oncology, University of North Carolina, Chapel Hill, North Carolina.
Division 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.
Department of Radiation Oncology, VU University Medical Center, Amsterdam, The Netherlands.
Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, Colorado.
London 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.

[Indexed for MEDLINE]

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