Room: AAPM ePoster Library
Purpose: Intraoperative Radiation Therapy (IORT) using a mobile linear accelerator involves placing physical applicators directly onto the desired treatment surface in the patient. Due to patient anatomy and the geometries of physical applicators, it is sometimes impossible to make flush contact between the treatment surface and the applicator. In these cases, a gap correction factor should be used to correctly calculate the monitor units for the treatment. This gap correction factor changes not only with increasing distance but also with changing scatter conditions past the end of the applicator. However, accurately measuring the actual gap distance in the operative setting is difficult. In this study we have designed and tested a new LIDAR based device that can accurately and rapidly measure these gap distances.
Methods: We built a mount that can attach to the end of IORT applicators. An aluminum rod affixes to the interior of the mount with a LIDAR chip on its end, which extends into the applicator. We measured gap distances for 3, 4, 7 and 10 cm diameter applicators on different colors of paper ( red, brown, black, white, and pink) with gaps ranging from 0-3 cm. We additionally measured these distances from a raw steak to the ends of the 4, 7, and 10 cm applicators. Measurements were performed with and without room lighting.
Results: LIDAR measurements onto all paper colors agreed with the physical distances for both 3 and 10 cm applicators within 1 mm. LIDAR measurements onto the steak surface agreed with actual physical distances for all applicators within 2 mm, with an absolute average error for all positions of 0.86 mm. Room lighting conditions had no effect on distance measurements.
Conclusion: Our LIDAR device can accurately measure physical gaps between a patients treatment surface and the end of an applicator.