Quantitative measurement of post-irradiation neck fibrosis based on the young modulus: description of a new method and clinical results.

Abstract

Postirradiation fibrosis is one of the most common late effects of radiation therapy for patients with head and neck carcinoma. An objective and quantitative method for its measurement is much desired, but the criteria currently used to score fibrosis are mostly semiquantitative and partially subjective. The Young Modulus (YM) is a physical parameter that characterizes the deformability of material to stress. The authors measured the YM in soft tissues of the neck, at defined reference points, using an ultrasound probe and computer algorithm that quantified the indentation (deformation) on tissue due to a measured, applied force. One hundred five patients who had received previous radiation therapy to the entire neck were assessed, and the results were compared with the hand palpation scores and with a functional parameter represented by the range of neck rotation, and all results were correlated with symptoms. The YM was obtained successfully in all patients examined. It had a significant positive correlation with the palpation score and a significant negative correlation with the range of neck rotation. The YM was significantly higher on the side of the neck that received a boost dose of radiation, although the corresponding palpation scores were similar. The results of all three measurement methods were correlated with symptoms. Postirradiation neck fibrosis can be measured in absolute units based on the YM. The results showed a significant correlation with hand palpation scores, with restriction of neck rotation, and with symptoms. Compared with the palpation method, the YM is more quantitative, objective, focused on small subregions, and better discriminates regions subject to differential radiation dose levels. Its inclusion in the Analytic category of the Late Effects of Normal Tissues-SOMA system should be considered to facilitate comparative studies.