Analysis of the movement of calcified lymph nodes during breathing

To identify and measure the respiratory-induced movement of calcified mediastinal lymph nodes.

Twenty-one patients receiving radiation therapy for primary lung or pleural tumors were noted to have calcification within one or more mediastinal lymph nodes. The breathing motion of 27 such nodes was measured with orthogonal fluoroscopic imaging during quiet respiration.

All 27 nodes showed some motion synchronous with breathing. The mean respiratory movement was 6.6 mm, 2.6 mm, and 1.4 mm in the craniocaudal, dorsoventral, and mediolateral planes, respectively. There was a significant difference in the amplitude of motion in the craniocaudal plane compared with movement in the other two directions (p < 0.001). No differences were seen in the movement of lymph nodes dependent on position within the mediastinum (supracarinal vs. infracarinal or hilar vs. mediastinal). Neither size of the primary tumor nor spirometric parameters were correlated with the amplitude of lymph node movement.

Mediastinal lymph nodes move during breathing, and this needs to be accounted for when the internal margin component of the PTV is defined. The amplitude of this movement is anisotropic and seems to be less than that reported for primary lung tumors. This should permit a modest reduction in the margin allowed for breathing movement around involved mediastinal nodes, particularly in the mediolateral and dorsoventral planes.