Determining the optimal surface tracking area on the stereotactic mask in brain stereotactic radiosurgery using thermo-optical surface-guided radiotherapy.

PURPOSE: Surface-guided radiotherapy (SGRT) using ExacTrac Dynamic (EXTD) combines the optical surface with "thermal" imaging. We investigated the relationship between surface temperature changes and position errors detected by EXTD and identified the optimal surface tracking area (STA) on a stereotactic mask for brain stereotactic radiosurgery.

METHODS

A phantom with a heat pad and a stereotactic mask over it was set up on the linac, and its surface was assigned to the STA. After powering on the heat pad, we investigated the change in the mask's surface temperature for a detected 1.0-mm position error. Subsequently, stereotactic masks were created for six volunteers. The temperatures of the forehead, nose, mouth, and cheek areas on the mask were measured using a thermography camera. We identified the temperature stabilization areas on the mask during the treatment.

RESULTS

Position errors were detected to be 1.0 mm when the surface temperature increased by approximately 0.5 °C in the phantom study. Next, the average temperature stabilization time on the mask was 4.2, 3.7, 2.3 and 1.8 min in the forehead, nose, mouth, and cheeks, respectively. The surface temperature of the mask stabilized after 4 min in the nose, mouth, and cheeks, except for the forehead area. However, the mask temperature of the nose and mouth areas decreased with the breathing (>1.0 °C) in five of the six volunteers.

CONCLUSION

Assigning the STA to areas exhibiting temperature stability (<0.5 °C) is crucial, and we recommend assigning the STA to the cheek area after fitting the stereotactic mask for 4 min.