Assessment of upright immobilization methods for abdominal and head-and-neck cancer treatments in a carbon ion radiotherapy setting.

BACKGROUND AND PURPOSE: Upright patient positioning is an emerging approach in radiotherapy that may overcome current limitations in carbon ion radiotherapy (CIRT). This study evaluated upright immobilization techniques for abdominal and head-and-neck (HN) cancers in a CIRT setting.

MATERIALS AND

METHODS

Ten volunteers were positioned on the Chair, a demo upright positioning system (Leo Cancer Care, USA). Three setups were evaluated: no immobilization devices, vacuum bags alone (ESFORM; Engineering System Co., Japan), and vacuum bags with a thermoplastic shell (Shellfitter; Kuraray Trading Co., Japan), called the "shell" setup. Interfractional and intrafractional errors were assessed using skin markers drawn on the abdominal and HN areas. Interfractional shifts per direction and Euclidean distances were calculated by comparing reference and repeated images. Intrafractional shifts per direction and Euclidean distances were calculated from images acquired over a 15-min period. Also, volunteers rated their comfort for each setup on a scale of 1-5. Differences in the interfractional and intrafractional motion, and comfort ratings between the three setups were investigated.

RESULTS

Significant differences (p < 0.05) in the interfractional Euclidean distances were observed between the three setups in both anatomical areas, while significant differences were observed in more shifts per direction in the abdominal case. The "shell" setup minimized intrafractional distances. No significant differences were observed in the comfort ratings between the setups.

CONCLUSION

Upright positioning in CIRT appears feasible. Further research is needed to refine immobilization techniques to support clinical implementation of upright positioning in CIRT.