Technical Note: Millimeter precision in ultrasound based patient positioning: Experimental quantification of inherent technical limitations. Issue 8 (30th November 2016)

• Record Type: Journal Article
• Authors: Ballhausen, Hendrik; Hieber, Sheila; Li, Minglun; Belka, Claus; Reiner, Michael
• Is Part Of: Medical physics. Volume 41:Issue 8(2014)Part 1
• Page Start: n/a
• Page End: n/a
• Publication Date: 2016-11-30
• Subjects: Therapeutic applications -- Ultrasonography -- Standards and calibration; biomedical ultrasonics -- calibration -- measurement errors -- phantoms -- radiation therapy; image guided radiation therapy -- prostate localization -- 3D ultrasound; Diagnosis using ultrasonic, sonic or infrasonic waves -- Radiation therapy -- Testing or calibrating of apparatus or arrangements provided for in groups G01D1/00 to G01D15/00 -- Biological material, e.g. blood, urine; Haemocytometers -- Calibrating of instruments or apparatus; Ultrasonography -- Calibration -- Cameras -- Infrared detectors -- Cancer -- Computed tomography -- Radiotherapy sources -- Medical radiation safety -- Infrared sources; Medical physics -- Periodicals; Medical physics; Geneeskunde; Natuurkunde; Toepassingen; Biophysics; Periodicals; Periodicals; Electronic journals; 610.153
• DOI: 10.1118/1.4890079
• Languages: English
• ISSNs: 0094-2405

Abstract

Abstract : Purpose: To identify the relevant technical sources of error of a system based on three‐dimensional ultrasound (3D US) for patient positioning in external beam radiotherapy. To quantify these sources of error in a controlled laboratory setting. To estimate the resulting end‐to‐end geometric precision of the intramodality protocol. Methods: Two identical free‐hand 3D US systems at both the planning‐CT and the treatment room were calibrated to the laboratory frame of reference. Every step of the calibration chain was repeated multiple times to estimate its contribution to overall systematic and random error. Optimal margins were computed given the identified and quantified systematic and random errors. Results: In descending order of magnitude, the identified and quantified sources of error were: alignment of calibration phantom to laser marks 0.78 mm, alignment of lasers in treatment vs planning room 0.51 mm, calibration and tracking of 3D US probe 0.49 mm, alignment of stereoscopic infrared camera to calibration phantom 0.03 mm. Under ideal laboratory conditions, these errors are expected to limit ultrasound‐based positioning to an accuracy of 1.05 mm radially. Conclusions: The investigated 3D ultrasound system achieves an intramodal accuracy of about 1 mm radially in a controlled laboratory setting. The identified systematic and random errors require an optimal clinical tumor volume to planning target volume margin of about 3 mm. These inherent technical limitations do not prevent clinical use, including hypofractionation or stereotactic body radiation therapy.