Abstract
PurposeTumor bed (TB) delineation based on preoperative magnetic resonance imaging (pre-MRI) fused with postoperative computed tomography (post-CT) were compared to post-CT only to define pre-MRI may aid in improving the accuracy of delineation.Methods and materialsThe pre-MRI imaging of 10 patients underwent radiotherapy (RT) after breast conserving surgery (BCS) were reviewed. Post-CT scans were acquired in the same prone position as pre-MRI. Pre-MRI and post-CT automatically match and then manual alignment was given to enhance fusion consistency. Three radiation oncologists and 2 radiologists delineated the clinical target volume (CTV) for CT-based. The gross target volume (GTV) of pre-MRI-based was determined by the volume of tumor acquired with 6 sequences: T1, T2, T2W-SPAIR, DWI, dyn-eTHRIVE and sdyn-eTHRIVE, expended 10 mm to form the CTV-pre-MRI. Planning target volume (PTV) for each sequence was determined by CTV extended 15 mm, trimmed to 3 mm from skin and the breast-chest wall interface. The variability of the TB delineation were developed as follows: the mean volume, conformity index (CI) and dice coefficient (DC).ResultsThe mean volumes of CTV and PTV delineated with CT were all larger than those with pre-MRI. The lower inter-observer variability was observed from PTV, especially in sdyn-eTHRIVE in all sequences. For each sequence of pre-MRI, all DCs were larger than post-CT, and the largest DC was observed by sdyn-eTHRIVE sequence fusion to post-CT. The overlap for PTV was significantly improved in the pre-MRI-based compared with the CT-based.ConclusionsTB volumes based on pre-MRI were smaller than post-CT with CVS increased. Pre-MRI provided a more precise definition of the TB with observers performed a smaller inter-observer variability than CT. Pre-MRI, especially in sdyn-eTHRIVE sequence, should help in reducing treatment volumes with the improved accuracy of TB delineation of adjuvant RT of breast cancer.
Highlights
Radiotherapy (RT) is an indispensable treatment for many patients with early breast cancer after breastconserving surgery (BCS) [1]
For each sequence of pre-magnetic resonance imaging (MRI), all dice coefficient (DC) were larger than post-computed tomography (CT), and the largest DC was observed by sdyn-eTHRIVE sequence fusion to postoperative CT (post-CT)
tumor bed (TB) volumes based on preoperative magnetic resonance imaging (pre-MRI) were smaller than post-CT with cavity visualisation score (CVS) increased
Summary
Radiotherapy (RT) is an indispensable treatment for many patients with early breast cancer after breastconserving surgery (BCS) [1]. A few clinical researches have been developed to improve the delineation of the TB, including the use of seroma cavity, preoperative notes, clinical palpation, surgical clips, surgical scar and ultrasound(US)/ CTimaging/mammography [6]. A previous study assessed the inter-observer variability of surgical bed delineation after BCS pointed out that the fusion of CT and MRI should be used for surgical bed delineation [8]. This study aimed to evaluate the reproducibility of TB delineation and localisation based on prone pre-MRI and post-CT imaging fusion. It aimed to compare the inter-observer variability between post-CT and preMRI
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