An automated workflow for patient-specific quality control of contour propagation.

Contour propagation is an essential component of adaptive radiotherapy, but current contour propagation algorithms are not yet sufficiently accurate to be used without manual supervision. Manual review of propagated contours is time-consuming, making routine implementation of real-time adaptive radiotherapy unrealistic. Automated methods of monitoring the performance of contour propagation algorithms are therefore required. We have developed an automated workflow for patient-specific quality control of contour propagation and validated it on a cohort of head and neck patients, on which parotids were outlined by two observers. Two types of error were simulated-mislabelling of contours and introducing noise in the scans before propagation. The ability of the workflow to correctly predict the occurrence of errors was tested, taking both sets of observer contours as ground truth, using receiver operator characteristic analysis. The area under the curve was 0.90 and 0.85 for the observers, indicating good ability to predict the occurrence of errors. This tool could potentially be used to identify propagated contours that are likely to be incorrect, acting as a flag for manual review of these contours. This would make contour propagation more efficient, facilitating the routine implementation of adaptive radiotherapy.

The suitability of common metrics for assessing parotid and larynx autosegmentation accuracy.

Contouring structures in the head and neck is time-consuming, and automatic seg-mentation is an important part of an adaptive radiotherapy workflow. Geometric accuracy of automatic segmentation algorithms has been widely reported, but there is no consensus as to which metrics provide clinically meaningful results. This study investigated whether geometric accuracy (as quantified by several commonly used metrics) was associated with dosimetric differences for the parotid and larynx, comparing automatically generated contours against manually drawn ground truth contours. This enabled the suitability of different commonly used metrics to be assessed for measuring automatic segmentation accuracy of the parotid and larynx. Parotid and larynx structures for 10 head and neck patients were outlined by five clinicians to create ground truth structures. An automatic segmentation algorithm was used to create automatically generated normal structures, which were then used to create volumetric-modulated arc therapy plans. The mean doses to the automatically generated structures were compared with those of the corresponding ground truth structures, and the relative difference in mean dose was calculated for each structure. It was found that this difference did not correlate with the geometric accuracy provided by several metrics, notably the Dice similarity coefficient, which is a commonly used measure of spatial overlap. Surface-based metrics provided stronger correlation and are, therefore, more suitable for assessing automatic seg-mentation of the parotid and larynx.

Relative plan robustness of step-and-shoot vs rotational intensity-modulated radiotherapy on repeat computed tomographic simulation for weight loss in head and neck cancer.

INTRODUCTION: Interfractional anatomical alterations may have a differential effect on the dose delivered by step-and-shoot intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT). The increased degrees of freedom afforded by rotational delivery may increase plan robustness (measured by change in target volume coverage and doses to organs at risk [OARs]). However, this has not been evaluated for head and neck cancer. MATERIALS AND METHODS: A total of 10 patients who required repeat computed tomography (CT) simulation and replanning during head and neck IMRT were included. Step-and-shoot IMRT and VMAT plans were generated from the original planning scan. The initial and second CT simulation scans were fused and targets/OAR contours transferred, reviewed, and modified. The plans were applied to the second CT scan and doses recalculated without repeat optimization. Differences between step-and-shoot IMRT and VMAT for change in target volume coverage and doses to OARs between first and second CT scans were compared by Wilcoxon signed rank test. RESULTS: There were clinically relevant dosimetric changes between the first and the second CT scans for both the techniques (reduction in mean D95% for PTV2 and PTV3, Dmin for CTV2 and CTV3, and increased mean doses to the parotid glands). However, there were no significant differences between step-and-shoot IMRT and VMAT for change in any target coverage parameter (including D95% for PTV2 and PTV3 and Dmin for CTV2 and CTV3) or dose to any OARs (including parotid glands) between the first and the second CT scans. CONCLUSIONS: For patients with head and neck cancer who required replanning mainly due to weight loss, there were no significant differences in plan robustness between step-and-shoot IMRT and VMAT. This information is useful with increased clinical adoption of VMAT.