# A multi-institutional comparison of retrospective deformable dose accumulation for online adaptive magnetic resonance-guided radiotherapy

## TL;DR

This study compares six methods for calculating radiation doses in adaptive MRI-guided radiotherapy, finding high agreement but also clinically relevant differences.

## Contribution

A multi-center evaluation of deformable dose accumulation methods in online-adaptive MRgRT using both a gold standard and clinical cases.

## Key findings

- DIR of clinical cases achieved DSC > 0.8 for up to 81.3% of contours.
- DVH ICC showed excellent reliability (>0.9) for most contours, but CDC differences were clinically relevant.
- Maximum HD95% of 73.3 mm was observed for the duodenum in a liver case.

## Abstract

•A multi-center study was performed comparing six different deformable image registration and dose accumulation implementations using a gold standard case with known deformations and five clinical cases which had been treated with magnetic resonance-guided radiotherapy (MRgRT).•Deformable image registration (DIR) of clinical cases resulted in Dice Similarity Coefficient (DSC) > 0.8 for up to 81.3% of contours and a variability of surface-DSC values depending on the implementation.•Dose volume histogram (DVH) related intraclass correlation coefficients (ICC) showed excellent reliability (>0.9) between different DVHs except for two, although considerable absolute differences in clinical dosimetric criteria were observed in the clinical cases.•The algorithms used in this study showed a generally high level of agreement, but significant differences were found between the clinical cases and the algorithms, which may have clinical relevance.

A multi-center study was performed comparing six different deformable image registration and dose accumulation implementations using a gold standard case with known deformations and five clinical cases which had been treated with magnetic resonance-guided radiotherapy (MRgRT).

Deformable image registration (DIR) of clinical cases resulted in Dice Similarity Coefficient (DSC) > 0.8 for up to 81.3% of contours and a variability of surface-DSC values depending on the implementation.

Dose volume histogram (DVH) related intraclass correlation coefficients (ICC) showed excellent reliability (>0.9) between different DVHs except for two, although considerable absolute differences in clinical dosimetric criteria were observed in the clinical cases.

The algorithms used in this study showed a generally high level of agreement, but significant differences were found between the clinical cases and the algorithms, which may have clinical relevance.

Application of different deformable dose accumulation (DDA) solutions makes institutional comparisons after online-adaptive magnetic resonance-guided radiotherapy (OA-MRgRT) challenging. The aim of this multi-institutional study was to analyze accuracy and agreement of DDA-implementations in OA-MRgRT.

One gold standard (GS) case deformed with a biomechanical-model and five clinical cases consisting of prostate (2x), cervix, liver, and lymph node cancer, treated with OA-MRgRT, were analyzed. Six centers conducted DDA using institutional implementations. Deformable image registration (DIR) and DDA results were compared using the contour metrics Dice Similarity Coefficient (DSC), surface-DSC, Hausdorff-distance (HD95%), and accumulated dose-volume histograms (DVHs) analyzed via intraclass correlation coefficient (ICC) and clinical dosimetric criteria (CDC).

For the GS, median DDA errors ranged from 0.0 to 2.8 Gy across contours and implementations. DIR of clinical cases resulted in DSC > 0.8 for up to 81.3% of contours and a variability of surface-DSC values depending on the implementation. Maximum HD95%=73.3 mm was found for duodenum in the liver case. Although DVH ICC > 0.90 was found after DDA for all but two contours, relevant absolute CDC differences were observed in clinical cases: Prostate I/II showed maximum differences in bladder V28Gy (10.2/7.6%), while for cervix, liver, and lymph node the highest differences were found for rectum D2cm3 (2.8 Gy), duodenum Dmax (7.1 Gy), and rectum D0.5cm3 (4.6 Gy).

Overall, high agreement was found between the different DIR and DDA implementations. Case- and algorithm-dependent differences were observed, leading to potentially clinically relevant results. Larger studies are needed to define future DDA-guidelines.