Inter-observer agreement of MRI-based XXXX delineation for preoperative radiotherapy boost in locally advanced @entity5 .

@entity1 @entity137 @entity5529 @entity5 @entity16178 @entity17470 @entity18086 @entity18246
BACKGROUND: While surgery remains the @entity5 treatment, organ-preservation is upcoming. Therefore, neo-adjuvant treatment should be optimized. By escalating doses, response can be increased. To limit @entity137 of boost, accurate gross @entity5 volume (GTV) definition is required. MRI, especially undeformed fast spin echo diffusion-weighted MRI (DWI), looks promising for delineation. However, inconsistencies between observers should be quantified before clinical implementation. We aim to find which MRI sequence (T2w, DWI or combination) is optimal and clinically useful for GTV definition by evaluating inter-observer agreement. METHODS: Locally advanced @entity5 @entity1 ( @entity5 <10cm from anal verge) were scanned on 3T MRI transverse T2w and DWI (b=800s/mm(2)). Three independent observers delineated T2w, DWI and combination (Combi) after training-set. Volumes, conformity index (CI), and maximum @entity5529 ( @entity5529 ) were calculated between any observer-pair per @entity1 per modality. RESULTS: Twenty-four consecutive @entity1 were included. One @entity1 had @entity18246 (4.2%), 19 @entity16178 (79.1%) and 4 cT4 (16.7%), with 2 clinical node negative (8.3%), 4 @entity17470 (16.7%), and 18 @entity18086 (75.0%) on MRI. From 24 @entity1 , 70 sequences were available (24x T2, 23x DWI, and 23x Combi). Between observers, no significant volume differences were observed per modality. T2 showed significantly largest volumes compared to DWI (mean difference 19.85ml, SD 17.42, p<0.0001) and Combi (mean difference 7.16ml, SD 11.58, p<0.0001). Mean CI was 0.70, 0.71 and 0.69 for T2, DWI and Combi respectively (p>0.61). Average @entity5529 was largest on T2 (18.60mm, max 31.40mm, min 9.20mm). DISCUSSION: Delineation on DWI resulted in delineation of the smallest volumes with similar consistency and mean distances, but with slightly lower Hausdorff distances compared to T2 and Combi. However, with lack of a gold standard it remains difficult to establish if delineations also represent true @entity5 . Study strengths were DWI adaptation to exclude geometrical distortions and training-set. DWI shows great potential for delineation purposes as long as sufficient experience exists and geometrical distortions are eliminated.
