Benefits for Head and Neck Positioning Using a Surface Image Guidance System

Abstract

<h3>Purpose/Objective(s)</h3> Surface-guided radiation therapy (SGRT) is an emerging technology that enables three-dimensional surfaces image guidance for radiotherapy. The technology is commonly employed in the setup for breast cancer patients; however, it would be challenging for head and neck cancer patients. The purpose of this study was to investigate the accuracy of surface image-guided positioning compared to conventional in-room-laser based positioning using marks on a thermoplastic mask for the head and neck patient. <h3>Materials/Methods</h3> Thirty patients were randomly selected for two groups: the surface image-guided positioning group (SGRT group) and the conventional in-room-laser based positioning group using marks on a thermoplastic mask (non-SGRT group). Total sixty patients received intensity-modulated radiotherapy using helical tomotherapy for head and neck cancer. For both groups, the positional errors for translational and rotational shifts were acquired by aligning the mega-voltage CT (MVCT) images in the first treatment fraction for the treatment planning kVCT images. In addition, the number of the additional MVCT scan for repositioning during all treatment fractions was counted. The reposition was performed when the rotational shift error was greater than 2.0°. The differences of the positional errors and the mean number of MVCT scans per fraction between the SGRT and non-SGRT groups were evaluated using the Mann-Whitney U test. <h3>Results</h3> The mean positional errors in the lateral, longitudinal, and vertical directions were as follows: -0.8±0.9, -3.0±2.6, and 0.7±1.4 mm in the SGRT group, and -1.3±1.5, -1.0±1.9, and 0.1±1.2 mm in the non-SGRT group. The only positional error in the longitudinal direction was significantly larger in the SGRT than non-SGRT groups (<i>p</i> < 0.05); however, the difference could be relatively small. The mean positional error of rotational shift in each axis was less than 0.2° in both groups, and there was no significant difference between the two groups. The mean number of MVCT scans per fraction in the SGRT and non-SGRT groups was 1.14 and 1.26 (total number; about 40 and 44 scans at 35 fractions), respectively. It was significantly lower in the SGRT group than in the non-SGRT group (<i>p</i> < 0.05). <h3>Conclusion</h3> Surface image-guided positioning resulted in a larger positional error in the longitudinal direction than conventional in-room-laser based positioning using marks on a thermoplastic mask. The difference could be relatively small. In addition, it contributed to the reduction of the additional MVCT scan for repositioning.