Tumor motion and deformation during external radiotherapy of bladder cancer.
OBJECTIVE
First, to quantify bladder-tumor motion in 3 dimensions during a 4-week to 5-week course of external radiotherapy. Second, to relate the motion to the tumor location on the bladder wall. Third, to extensively evaluate gross tumor volume (GTV) shape and volume changes during the course of the treatment.


METHODS
Multiple repeat computed tomography (CT) images were obtained for 21 bladder cancer patients. These scans were matched to the rigid bony anatomy. For each patient, the main direction and magnitude of the tumor movement was determined by use of principle-component analysis. To study GTV shape changes, all GTVs were registered to the GTV in the planning CT scan, and the residual shape errors were determined by measurement of edge variations perpendicular to the median surface.


RESULTS
Gross tumor volume translations were largest in cranial-caudal and anterior-posterior direction (SD, 0.1 to approximately 0.9 cm). The translations were strongly correlated with the tumor location on the bladder wall. The average value of the local standard deviations of the GTV shape ranged from 0.1 to approximately 0.35 cm.


CONCLUSIONS
Despite large differences in bladder filling, variations in GTV shape were small compared with variations in GTV position. Geometric uncertainties in the GTV position depended strongly on the tumor location on the bladder wall.
Department of Radiation Oncology, The Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands.
Heidi T
HT
Lotz
Floris J
FJ
Pos
Maarten C C M
MC
Hulshof
Marcel
M
van Herk
Joos V
JV
Lebesque
Joop C
JC
Duppen
Peter
P
Remeijer
D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008297:Male; D009068:Movement; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods; D001743:Urinary Bladder / Q000000981:diagnostic imaging / Q000473:pathology; D001749:Urinary Bladder Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*