Nonrandom intrafraction target motions and general strategy for correction of spine stereotactic body radiotherapy.
OBJECTIVE
To characterize nonrandom intrafraction target motions for spine stereotactic body radiotherapy and to develop a method of correction via image guidance. The dependence of target motions, as well as the effectiveness of the correction strategy for lesions of different locations within the spine, was analyzed.


METHODS
Intrafraction target motions for 64 targets in 64 patients treated with a total of 233 fractions were analyzed. Based on the target location, the cases were divided into three groups, i.e., cervical (n = 20 patients), thoracic (n = 20 patients), or lumbar-sacrum (n = 24 patients) lesions. For each case, time-lag autocorrelation analysis was performed for each degree of freedom of motion that included both translations (x, y, and z shifts) and rotations (roll, yaw, and pitch). A general correction strategy based on periodic interventions was derived to determine the time interval required between two adjacent interventions, to overcome the patient-specific target motions.


RESULTS
Nonrandom target motions were detected for 100% of cases regardless of target locations. Cervical spine targets were found to possess the highest incidence of nonrandom target motion compared with thoracic and lumbar-sacral lesions (p < 0.001). The average time needed to maintain the target motion to within 1 mm of translation or 1 degrees of rotational deviation was 5.5 min, 5.9 min, and 7.1 min for cervical, thoracic, and lumbar-sacrum locations, respectively (at 95% confidence level).


CONCLUSIONS
A high incidence of nonrandom intrafraction target motions was found for spine stereotactic body radiotherapy treatments. Periodic interventions at approximately every 5 minutes or less were needed to overcome such motions.
Ma
Lijun
L
Department of Radiation Oncology, University of California, San Francisco, California 94143, USA. lijunma@radonc.ucsf.edu
Sahgal
Arjun
A
Hossain
Sabbir
S
Chuang
Cynthia
C
Descovich
Martina
M
Huang
Kim
K
Gottschalk
Alex
A
Larson
David A
DA
D000465:Algorithms; D002138:Calibration; D002574:Cervical Vertebrae; D019583:Dose Fractionation, Radiation; D006801:Humans; D008159:Lumbar Vertebrae; D009068:Movement; D011859:Radiography; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012447:Sacrum; D013125:Spinal Neoplasms / Q000000981:diagnostic imaging / Q000601:surgery*; D013679:Technology, Radiologic / Q000379:methods; D013904:Thoracic Vertebrae; D013997:Time Factors