Cherenkoscopy based patient positioning validation and movement tracking during post-lumpectomy whole breast radiation therapy.

To investigate Cherenkov imaging (Cherenkoscopy) based patient positioning and movement tracking during external beam radiation therapy (EBRT). In a phase 1 clinical trial, including 12 patients undergoing post-lumpectomy whole breast irradiation, Cherenkov emission was imaged with a time-gated ICCD camera synchronized to the LINAC pulse output, during different fractions of the treatment. Patients were positioned with the aid of the AlignRT system in the beginning of each treatment session. Inter-fraction setup variation was studied by rigid image registrations between images acquired at individual treatments to the average image from all imaged treatment fractions. The amplitude of respiratory motion was calculated from the registration of each frame of Cherenkov images to the reference. A Canny edge detection algorithm was utilized to highlight the beam field edges and biological features provided by major blood vessels apparent in the images. Real-time Cherenkoscopy can monitor the treatment delivery, patient motion and alignment of the beam edge to the treatment region simultaneously. For all the imaged fractions, the patient positioning discrepancies were within our clinical tolerances (3 mm in shifts and 3 degree in pitch angle rotation), with 4.6% exceeding 3 mm but still within 4 mm in shifts. The average discrepancy of repetitive patient positioning was 1.22 mm in linear shift and 0.34 degrees in rotational pitch, consistent with the accuracy reported by the AlignRT system. The edge detection algorithm enhanced features such as field edges and blood vessels. Patient positioning discrepancies and respiratory motion retrieved from rigid image registration were consistent with the edge enhanced images. Besides positioning discrepancies caused by globally inaccurate setups, edge enhanced blood vessels indicate the existence of deformations within the treatment region, especially for large patients. Real-time Cherenkoscopy imaging during EBRT is a novel imaging tool that can be used for treatment monitoring, patient positioning and motion tracking.