Detection of organ movement in cervix cancer patients using a fluoroscopic electronic portal imaging device and radiopaque markers.
OBJECTIVE
To investigate the use of a fluoroscopic electronic portal imaging device (EPID) and radiopaque markers to detect internal cervix movement.


METHODS
For 10 patients with radiopaque markers clamped to the cervix, electronic portal images were made during external beam irradiation. Bony structures and markers in the portal images were registered with the same structures in the corresponding digitally reconstructed radiographs of the planning computed tomogram.


RESULTS
The visibility of the markers in the portal images was good, but their fixation should be improved. Generally, the correlation between bony structure displacements and marker movement was poor, the latter being substantially larger. The standard deviations describing the systematic and random bony anatomy displacements were 1.2 and 2.6 mm, 1.7 and 2.9 mm, and 1.6 and 2.7 mm in the lateral, cranial-caudal, and dorsal-ventral directions, respectively. For the marker movement those values were 3.4 and 3.4 mm, 4.3 and 5.2 mm, 3.2 and 5.2 mm, respectively. Estimated clinical target volume to planning target volume (CTV-PTV) planning margins (approximately 11 mm) based on the observed overall marker displacements (bony anatomy + internal cervix movement) are only marginally larger than the margins required to account for internal marker movement alone.


CONCLUSIONS
With our current patient setup techniques and methods of setup verification and correction, the required CTV-PTV margins are almost fully determined by internal organ motion. Setup verification and correction using radiopaque markers might allow decreasing those margins, but technical improvements are needed.
Kaatee
Robert S J P
RS
Department of Radiation Oncology, University Hospital Rotterdam-Daniel den Hoed Cancer Center, Rotterdam, The Netherlands. kaatee@kfih.azr.nl
Olofsen
Manouk J J
MJ
Verstraate
Marjolein B J
MB
Quint
Sandra
S
Heijmen
Ben J M
BJ
D002584:Cervix Uteri / Q000000981:diagnostic imaging*; D005260:Female; D005471:Fluoroscopy / Q000295:instrumentation*; D006801:Humans; D009068:Movement; D010384:Pelvic Bones / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D002583:Uterine Cervical Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*