Toward correcting drift in target position during radiotherapy via computer-controlled couch adjustments on a programmable Linac

• Published in: Medical physics (Lancaster) Vol. 40; no. 5; pp. 051719 - n/a
• Main Authors: McNamara, Joseph E., Regmi, Rajesh, Michael Lovelock, D., Yorke, Ellen D., Goodman, Karyn A., Rimner, Andreas, Mostafavi, Hassan, Mageras, Gig S.
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01-05-2013
• Subjects: 60 APPLIED LIFE SCIENCES; adaptive radiotherapy; Analysis of motion; biomedical equipment; Biomedical instrumentation and transducers, including micro‐electro‐mechanical systems (MEMS); Cameras; Cancer; Computed tomography; Computerised tomographs; computerised tomography; COMPUTERIZED TOMOGRAPHY; CONTROL SYSTEMS; Digital computing or data processing equipment or methods, specially adapted for specific applications; DOSES; Feasibility Studies; FILTERS; Humans; Image analysis; Image data processing or generation, in general; image motion analysis; IMAGE PROCESSING; Kalman filters; LINEAR ACCELERATORS; mean‐position estimation; medical control systems; medical image processing; MONITORS; Motion compensation; Movement; PATIENTS; PERIODICITY; PHANTOMS; Phantoms, Imaging; Pneumodyamics, respiration; pneumodynamics; position control; radiation therapy; Radiation therapy equipment; Radiation Therapy Physics; RADIOLOGY AND NUCLEAR MEDICINE; RADIOTHERAPY; Radiotherapy Dosage; Radiotherapy, Computer-Assisted - methods; Real time information delivery; RESPIRATION; respiratory motion; Robotics; Sequence analysis; SIMULATION; target tracking; tracking; Tracking devices; Treatment strategy; tracking; mean-position estimation; adaptive radiotherapy; respiratory motion
• ISSN: 0094-2405; 2473-4209; 0094-2405
• DOI: 10.1118/1.4802736

Purpose:
Real-time tracking of respiratory target motion during radiation therapy is technically challenging, owing to rapid and possibly irregular breathing variations. The authors report on a method to predict and correct respiration-averaged drift in target position by means of couch adjustments on an accelerator equipped with such capability.
Methods:
Dose delivery is broken up into a sequence of 10 s field segments, each followed by a couch adjustment based on analysis of breathing motion from an external monitor as a surrogate of internal target motion. Signal averaging over three respiratory cycles yields a baseline representing target drift. A Kalman filter predicts the baseline position 5 s in advance, for determination of the couch correction. The method's feasibility is tested with a motion phantom programmed according to previously recorded patient signals. Computed couch corrections are preprogrammed into a research mode of an accelerator capable of computer-controlled couch translations synchronized with the motion phantom. The method's performance is evaluated with five cases recorded during hypofractionated treatment and five from respiration-correlated CT simulation, using a root-mean-squared deviation (RMSD) of the baseline from the treatment planned position.
Results:
RMSD is reduced in all 10 cases, from a mean of 4.9 mm (range 2.7–9.4 mm) before correction to 1.7 mm (range 0.7–2.3 mm) after correction. Treatment time is increased ∼5% relative to that for no corrections.
Conclusions:
This work illustrates the potential for reduction in baseline respiratory drift with periodic adjustments in couch position during treatment. Future treatment machine capabilities will enable the use of “on-the-fly” couch adjustments during treatment.