Defining the clinical target volume for bladder cancer radiotherapy treatment planning.
OBJECTIVE
There are currently no data for the expansion margin required to define the clinical target volume (CTV) around bladder tumors. This information is particularly relevant when perivesical soft tissue changes are seen on the planning scan. While this appearance may reflect extravesical extension (EVE), it may also be an artifact of previous transurethral resection (TUR).


METHODS
Eighty patients with muscle-invasive bladder cancer who had undergone radical cystectomy were studied. All patients underwent preoperative TUR and staging computed tomography (CT) scans. The presence and extent of tumor growth beyond the outer bladder wall was measured radiologically and histopathologically.


RESULTS
Forty one (51%) patients had histologically confirmed tumor extension into perivesical fat. The median and mean extensions beyond the outer bladder wall were 1.7 and 3.1 mm, respectively. Thirty five (44%) patients had EVE, as seen on CT scans. The sensitivity and specificity of CT scans for EVE were 56% and 79%, respectively. False-positive results were infrequent and not affected by either the timing or the amount of tissue resected at TUR. CT scans consistently tended to overestimate the extent of EVE. Tumor size and the presence of either lymphovascular invasion or squamoid differentiation predict a greater extent of EVE.


CONCLUSIONS
In patients with radiological evidence of extravesical disease, the CTV should comprise the outer bladder wall plus a 10-mm margin. In patients with no evidence of extravesical disease on CT scans, the CTV should be restricted to the outer bladder wall plus a 6-mm margin. These recommendations would encompass microscopic disease extension in 90% of cases.
Jenkins
Peter
P
Gloucestershire Oncology Centre, Cheltenham General Hospital, Cheltenham, United Kingdom. peter.jenkins@glos.nhs.uk
Anjarwalla
Salim
S
Gilbert
Hugh
H
Kinder
Richard
R
D000273:Adipose Tissue / Q000000981:diagnostic imaging / Q000473:pathology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy / Q000601:surgery; D002295:Carcinoma, Transitional Cell / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy / Q000601:surgery; D015653:Cystectomy; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D047368:Tumor Burden; D001743:Urinary Bladder / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D001749:Urinary Bladder Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology* / Q000532:radiotherapy* / Q000601:surgery