A comparison of three different adaptive strategies in image-guided radiotherapy of bladder cancer.
The urinary bladder shows considerable individual variation in shape and position during a course of radiotherapy (RT). In this study we have developed and compared three different adaptive RT (ART) strategies for bladder cancer involving daily cone beam CT (CBCT) imaging and plan selection.


METHODS
Ten patients treated for bladder cancer had daily CBCTs acquired that were registered online using bony anatomy registration. Seven patients received intensity modulated RT (IMRT) with a simultaneous integrated boost (SIB) technique to the bladder and pelvic lymph nodes. Three patients received treatment to the bladder only. Retrospectively, we compared three ART strategies that were all based on daily selection of the most suitable plan from a library consisting of three IMRT-plans corresponding to a small, medium and large target volume. ART method A utilised population-based margins while methods B and C used the bladder as seen on CBCT-scans from the first week of treatment; method B without delineation of the bladder on CBCT and method C with delineation of the bladder. Total dose distributions were calculated using the planning CT. For each patient, we calculated ratios of the dose volume histograms (DVHs) for the three ART strategies relative to non-adaptive therapy.


RESULTS
The inter-patient variation was large for all three ART strategies. The mean ratios of the volumes receiving 57 Gy or more (corresponding to 95% of prescribed dose) for methods A, B and C were 0.66 (SD: 0.11), 0.67 (SD: 0.13) and 0.67 (SD: 0.16) respectively when compared to the non-adaptive plan.


CONCLUSIONS
When using any of the ART strategies, it is possible to reduce significantly the volumes receiving high doses compared to the use of a standard non-adaptive plan. The differences in dose volume parameters between the three methods were small compared with the differences from the standard plan.
Vestergaard
Anne
A
Department of Medical Physics, Aarhus University Hospital - Arhus Sygehus, DK-8000 Aarhus C, Denmark. annveste@rm.dk
Søndergaard
Jimmi
J
Petersen
Jørgen B
JB
Høyer
Morten
M
Muren
Ludvig Paul
LP
D000368:Aged; D000369:Aged, 80 and over; D002277:Carcinoma / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D009929:Organ Size; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods; D047368:Tumor Burden / Q000528:radiation effects; D001743:Urinary Bladder / Q000473:pathology / Q000528:radiation effects; D001749:Urinary Bladder Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*