Accuracy of software-assisted contour propagation from planning CT to cone beam CT in head and neck radiotherapy

Abstract

Background: Autocontouring improves workflow in computed tomography (CT)-based dose planning, but could also potentially play a role for optimal use of daily cone beam CT (CBCT) in adaptive radiotherapy. This study aims to determine the accuracy of a deformable image registration (DIR) algorithm for organs at risk (OAR) in the neck region, when applied to CBCT. Material and methods: For 30 head and neck cancer (HNC) patients 14 OARs including parotid glands, swallowing structures and spinal cord were delineated. Contours were propagated by DIR from CT to the CBCTs of the first and last treatment fraction. An indirect approach, propagating contours to the first CBCT and from there to the last CBCT was also tested. Propagated contours were compared to manually corrected contours by Dice similarity coefficient (DSC) and Hausdorff distance (HD). Dose was recalculated on CBCTs and dosimetric consequences of uncertainties in DIR were reviewed. Results: Mean DSC values of !0.8 were considered adequate and were achieved in tongue base (0.91), esophagus (0.85), glottic (0.81) and supraglottic larynx (0.83), inferior pharyngeal constrictor muscle (0.84), spinal cord (0.89) and all salivary glands in the first CBCT. For the last CBCT by direct propagation, adequate DSC values were achieved for tongue base (0.85), esophagus (0.84), spinal cord (0.87) and all salivary glands. Using indirect propagation only tongue base (0.80) and parotid glands (0.87) were !0.8. Mean relative dose difference between automated and corrected contours was within ±2.5% of planed dose except for esophagus inlet (-4.5%) and esophagus (5.0%) for the last CBCT using indirect propagation. Conclusion: Compared to manually corrected contours, the DIR algorithm was accurate for use in CBCT images of HNC patients and the minor inaccuracies had little consequence for mean dose in most clinically relevant OAR. The method can thus enable a more automated segmentation of CBCT for use in adaptive radiotherapy.

Monitoring anatomical changes of individual patients using statistical process control during head-and-neck radiotherapy

“…Precision of PG propagation using DIR was evaluated by comparing these results against independent radiation oncologist CBCT re-contours (Supplementary Data H) and were found to be in excellent agreement with values reported in literature [28][29][30]. Well aligned to literature [16], the PGs included in this study demonstrated an average volume decrease of 21% and an average medial shift of 2.6 mm during HNRT.…”

Improved dosimetric accuracy with semi‐automatic contour propagation of organs‐at‐risk in glioblastoma patients undergoing chemoradiation

“…In this study, we show the feasibility of semi‐automated contour propagation, using deformable registration of the manual contours from the prior time point. Using manually corrected semi‐automatically propagated contours is similar to our daily clinical workflow in which a radiation oncologist reviews and corrects the work of a resident, which has been reported previously …”

Analysis of dose using CBCT and synthetic CT during head and neck radiotherapy: A single centre feasibility study

“…Precise immobilisation and image guided RT (IGRT) is crucial to minimise these effects. IGRT allows set-up errors to be corrected prior to treatment delivery and ensures the planned dose is consistently delivered throughout treatment [8][9][10][11][12].…”