The Elasticity of the Sternocleidomastoid Muscle before and at the End of Three-dimensional Conformal Radiotherapy

 
Purpose:
Sternocleidomastoid muscles are one of the most important neck muscles, which play an important role in the position of the neck. Head and neck Radiotherapy is the cause of severe Sternocleidomastoid muscle contractions. The aim of this study is to present a non-invasive method based on the extraction of muscle biomechanical parameters resulting from high-frequency ultrasound images to extract muscle dose response.
Methods:
Sequential ultrasound images were recorded with a 14 MHz frequency imaging system. The muscle’s mechanical parameters were extracted by the motion estimation
algorithm (block-matching). Reproducibility and validation of the method were done manually. Correlation between two automatic and manual methods was done with Pearson correlation analysis. The block-matching algorithm was used to estimate the muscle wall’s longitudinal movement. In this method, two blocks with specific dimensions were selected as reference blocks in the first frame. The way it works is to find the blocks in the next frames that have the most compliance with the reference blocks. The longitudinal displacement vector is the result of the difference between the two blocks in different frames. By using this algorithm, one patient with tongue cancer was examined once before the start of radiotherapy and again at the end.
Results:
A significant correlation between automatic and manual methods was obtained with a correlation coefficient of more than 0.79. Muscle’s shear modulus increased significantly at the end of radiotherapy which indicated an increase in muscle stiffness during the 60 Gy absorbed dose (p<0.05).
Conclusion:
In this study, a non-invasive method based on the extraction of muscle biomechanical parameters with processing of high-frequency ultrasound images to follow up radiation damage is concluded. The block matching algorithm is reliable for distinguishing the elasticity of Sternocleidomastoid muscle before and at the end of radiotherapy.