BACKGROUND: The bladder is a @entity5 site well suited for adaptive radiotherapy (ART) due to large inter-fractional changes, but it also displays considerable intra-fractional motion. The aim of this study was to assess target coverage with a clinically applied method for plan selection ART and to estimate population-based and @entity1 -specific intra-fractional margins, also relevant for a future re-optimisation strategy. MATERIAL AND METHODS: Nine @entity1 treated in a clinical phase II ART trial of daily plan selection for @entity150 were included. In the library plans, 5 mm isotropic margins were added to account for intra-fractional changes. Pre-treatment and weekly repeat magnetic resonance imaging (MRI) series were acquired in which a full three-dimensional (3D) volume was scanned every second min for 10 min (a total of 366 scans in 61 series). Initially, the bladder clinical target volume (CTV) was delineated in all scans. The t = 0 min scan was then rigidly registered to the planning computed tomography (CT) and plan selections were simulated using the CTV_0 (at t = 0 min). To assess intra-fractional motion, coverage of the CTV_10 (at t = 10 min) was quantified using the applied @entity343 . Population-based margins were calculated using the van Herk margin recipe while @entity1 -specific margins were calculated using a linear model. RESULTS: For 49% of the cases, the CTV_10 extended more than 5 mm outside the CTV_0. However, in 58 of the 61 cases (97%) CTV_10 was covered by the selected @entity343 . Population-based margins of 14 mm @entity43500 / @entity9659 , 9 mm Post and 5 mm Inf/Lat were sufficient to cover the bladder. Using @entity1 -specific margins, the overlap between @entity343 and bowel-cavity was reduced from 137 cm(3) with the plan selection strategy to 24 cm(3). CONCLUSION: In this phase II ART trial, 5 mm isotropic margin for intra-fractional motion was sufficient even though considerable intra-fractional motion was observed. In online re-optimised ART, population-based margin can be applied although @entity1 -specific margins are preferable.

Intra-fractional bladder motion and margins in adaptive radiotherapy for XXXX .

@entity1 :: ('9606', 'Species') :: ['patients', 'patient'] @entity5 :: ('MESH:D009369', 'Disease') :: ['tumour'] @entity343 :: ('187978', 'Species') :: ['PTV'] @entity43500 :: ('9709', 'Gene') :: ['Sup'] @entity150 :: ('MESH:D001749', 'Disease') :: ['bladder cancer'] @entity9659 :: ('293', 'Gene') :: ['Ant']
@entity150 :: (MESH:D001749,Disease) :: ['urinary bladder cancer']
