Assessment of bladder motion for clinical radiotherapy practice using cine-magnetic resonance imaging.
OBJECTIVE
Organ motion is recognized as the principal source of inaccuracy in bladder radiotherapy (RT), but there is currently little information on intrafraction bladder motion.


METHODS
We used cine-magnetic resonance imaging (cine-MRI) to study bladder motion relevant to intrafraction RT delivery. On two occasions, a 28 minute cine-MRI sequence was acquired from 10 bladder cancer patients and 5 control participants immediately after bladder emptying, after abstinence from drinking for the preceding hour. From the resulting cine sequences, bladder motion was subjectively assessed. To quantify bladder motion, the bladder was contoured in imaging volume sets at 0, 14, and 28 min to measure changes to bladder volumes, wall displacements, and center of gravity (COG) over time.


RESULTS
The dominant source of bladder motion during imaging was bladder filling (up to 101% volume increase); rectal and small bowel movements were transient, with minimal impact. Bladder volume changes were similar for all participants. However for bladder cancer patients, wall displacements were larger (up to 58 mm), less symmetrical, and more variable compared with nondiseased control bladders.


CONCLUSIONS
Significant and individualized intrafraction bladder wall displacements may occur during bladder RT delivery. This important source of inaccuracy should be incorporated into treatment planning and verification.
McBain
Catherine A
CA
Academic Department of Radiation Oncology, The University of Manchester, Christie Hospital NHS Foundation Trust, Wilmslow Road, Manchester, United Kingdom.
Khoo
Vincent S
VS
Buckley
David L
DL
Sykes
Jonathan S
JS
Green
Melanie M
MM
Cowan
Richard A
RA
Hutchinson
Charles E
CE
Moore
Christopher J
CJ
Price
Patricia M
PM
D000368:Aged; D016022:Case-Control Studies; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D007421:Intestine, Small / Q000033:anatomy & histology; D019028:Magnetic Resonance Imaging, Cine; D008297:Male; D008875:Middle Aged; D009068:Movement; D009929:Organ Size; D011446:Prospective Studies; D012007:Rectum / Q000033:anatomy & histology; D015203:Reproducibility of Results; D047368:Tumor Burden; D001743:Urinary Bladder / Q000033:anatomy & histology*; D001749:Urinary Bladder Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D014556:Urine