Assessment of neck tissue fibrosis using an ultrasound palpation system: a feasibility study

Fibrotic change in the soft tissue of the neck is a common side-effect after radiotherapy treatment for cancers of the head and neck region. The development of a quantitative approach for the assessment of neck tissue stiffness using an ultrasound palpation system (UPS) is reported. A testing protocol was established with the participation of eight normal subjects and four patients who had neck fibrosis after previous radiotherapy to the neck. Six reference sites were assessed on each side of the neck in each subject. Site-dependence, inter-observer variability, and intra-observer variability were further evaluated by measurement of sites 1 cm anterior, posterior, superior and inferior to two of the reference sites on each side of the neck, and by repeating measurements using a second observer on the same occasion and using the same observer one week afterwards. The mean tissue Young's modulus for normal subjects was 12.8 +/- 3.9 kPa, and that of the radiotherapy-treated patients ranged from 46.4 to 108.3 kPa. The modulus shows limited variation among anatomical sub-sites within the neck. For a confidence level of 95%, there was a variation of +/- 14.2% for site-dependence, +/- 15.2% for inter-observer, and +/- 7.2% for intra-observer tests for the group of normal subjects. The variation in the patients was +/- 13.6% for site-dependence, and +/- 13.1% for the inter-observer test.