Radial displacement of clinical target volume in node negative head and neck cancer

Abstract

Purpose: To evaluate the radial displacement of clinical target volume in the patients with node negative head and neck (H&N) cancer and to quantify the relative positional changes compared to that of normal healthy volunteers.

Materials and methods: Three node-negative H&N cancer patients and five healthy volunteers were enrolled in this study. For setup accuracy, neck thermoplastic masks and laser alignment were used in each of the acquired computed tomography (CT) images. Both groups had total three sequential CT images in every two weeks. The lymph node (LN) level of the neck was delineated based on the Radiation Therapy Oncology Group (RTOG) consensus guideline by one physician. We use the second cervical vertebra body as a reference point to match each CT image set. Each of the sequential CT images and delineated neck LN levels were fused with the primary image, then maximal radial displacement was measured at 1.5 cm intervals from skull base (SB) to caudal margin of LN level V, and the volume differences at each node level were quantified.

Results: The mean radial displacements were 2.26 (±1.03) mm in the control group and 3.05 (±1.97) in the H&N cancer patients. There was a statistically significant difference between the groups in terms of the mean radial displacement (p = 0.03). In addition, the mean radial displacement increased with the distance from SB. As for the mean volume differences, there was no statistical significance between the two groups.

Conclusion: This study suggests that a more generous radial margin should be applied to the lower part of the neck LN for better clinical target coverage and dose delivery.

Keywords: Head and neck neoplasms; Image-guided; Lymph nodes; Radiotherapy.

Fig. 1

Delineation of each neck node according to Radiation Therapy Oncology Group (RTOG) consensus guideline.

Fig. 2

Cervical vertebra delineation (C2, axis) for bony landmark based fusion.

Fig. 3

Manual measurement of maximal radial displacement at 1.5cm interval after bony landmark (C2, axis) based fusion.

Fig. 4

(A) Mean radial displacement in patients and control group (from skull base to neck lymph node (LN) level V inferior margin at 1.5 cm interval), (B) group mean radial displacement from skull base to level V; Spearman's rho correlation coefficient = 0.638 , p < 0.001.

Fig. 5

(A) Mean volume differences at each node level, (B) group mean volume differences at each node level. RP, retropharyngeal; LV, level.