Ultrasound imaging to assess inter- and intra-fraction motion during bladder radiotherapy and its potential as a verification tool.
OBJECTIVE
Organ motion is the principle source of error in bladder cancer radiotherapy. The aim of this study was to evaluate ultrasound bladder volume measurement as a surrogate measure of organ motion during radiotherapy: (1) to assess inter- and intra-fraction bladder variation and (2) as a potential treatment verification tool.


METHODS
Twenty patients receiving radical radiotherapy for bladder cancer underwent post-void ultrasound bladder volume measurement at the time of radiotherapy treatment planning (RTP), and immediately before (post-void) and after receiving daily fractions.


RESULTS
Ultrasound bladder volume measurement was found to be a simple and acceptable method to estimate relative bladder volume changes. Six patients showed significant changes to post-void bladder volume over the treatment course (P<0.05). The mean inter-fraction post-void bladder volume of five patients exceeded their RTP ultrasound bladder volume by more than 50%. Intra-fraction bladder volume increased on 275/308 (89%) assessed fractions, with the mean intra-fraction volume increases of seven patients exceeding their RTP ultrasound bladder volume by more than 50%.


CONCLUSIONS
Both day-to-day bladder volume variation and bladder filling during treatment should be considered in RTP and delivery. Ultrasound may provide a practical daily verification tool by: supporting volume limitation as a method of treatment margin reduction; allowing detection of patients who may require interventions to promote bladder reproducibility; and identifying patients with prominent volume changes for the selective application of more advanced adaptive/image-guided radiotherapy techniques.
McBain
C A
CA
Academic Department of Radiation Oncology, Christie Hospital NHS Trust, Manchester, UK.
Green
M M
MM
Stratford
J
J
Davies
J
J
McCarthy
C
C
Taylor
B
B
McHugh
D
D
Swindell
R
R
Khoo
V
V
Price
P
P
D000368:Aged; D000369:Aged, 80 and over; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D009929:Organ Size; D011446:Prospective Studies; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation*; D015203:Reproducibility of Results; D018084:Ultrasonography, Interventional / Q000379:methods*; D001749:Urinary Bladder Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*