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. 2024 Oct 28:32:100662.
doi: 10.1016/j.phro.2024.100662. eCollection 2024 Oct.

Comparison of online adaptive and non-adaptive magnetic resonance image-guided radiation therapy in prostate cancer using dose accumulation

Martina Murr  1 , Daniel Wegener  2   3 , Simon Böke  2 , Cihan Gani  2 , David Mönnich  1 , Maximilian Niyazi  2 , Moritz Schneider  1 , Daniel Zips  2   4   5 , Arndt-Christian Müller  2   6 , Daniela Thorwarth  1
Affiliations

Comparison of online adaptive and non-adaptive magnetic resonance image-guided radiation therapy in prostate cancer using dose accumulation

Martina Murr et al. Phys Imaging Radiat Oncol. .

Abstract

Background and purpose: Conventional image-guided radiotherapy (conv-IGRT) is standard in prostate cancer (PC) but does not account for inter-fraction anatomical changes. Online-adaptive magnetic resonance-guided RT (OA-MRgRT) may improve organ-at-risk (OARs) sparing and clinical target volume (CTV) coverage. The aim of this study was to analyze accumulated OAR and target doses in PC after OA-MRgRT and conv-IGRT in comparison to pre-treatment reference planning (refPlan).

Material and methods: Ten patients with PC, previously treated with OA-MRgRT at the 1.5 T MR-Linac (20x3Gy), were included. Accumulated OA-MRgRT doses were determined by deformably registering all fraction's MR-images. Conv-IGRT was simulated through rigid registration of the planning computed tomography with each fraction's MR-image for dose mapping/accumulation. Dose-volume parameters (DVPs), including CTV D50% and D98%, rectum, bladder, urethra, Dmax and V56Gy for OA-MRgRT, conv-IGRT and refPlan were compared using the Wilcoxon signed-rank test. Clinical relevance of accumulated dose differences was analyzed using a normal-tissue complication-probability model.

Results: CTV-DVPs were comparable, whereas OA-MRgRT yielded decreased median OAR-DVPs compared to conv-IGRT, except for bladder V56Gy. OA-MRgRT demonstrated significantly lower median rectum Dmax over conv-IGRT (59.1/59.9 Gy, p = 0.006) and refPlan (60.1 Gy, p = 0.012). Similarly, OA-MRgRT yielded reduced median bladder Dmax compared to conv-IGRT (60.0/60.4 Gy, p = 0.006), and refPlan (61.2 Gy, p = 0.002). Overall, accumulated dose differences were small and did not translate into clinically relevant effects.

Conclusion: Deformably accumulated OA-MRgRT using 20x3Gy in PC showed significant but small dosimetric differences comparted to conv-IGRT. Feasibility of a dose accumulation methodology was demonstrated, which may be relevant for evaluating future hypo-fractionated OA-MRgRT approaches.

Keywords: Deformable image registration; Dose accumulation; MR-Linac; MR-guided Radiotherapy; Prostate Cancer.

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Conflict of interest statement

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: The author Daniela Thorwarth is an Editor-in-Chief for Physics and Imaging in Radiation Oncology and was not involved in the editorial review or the decision to publish this article. MM and DT report institutional collaborations including financial and non-financial support by Elekta AB, Philips, TheraPanacea, Dr. Sennewald, Brainlab and PTW Freiburg. MM, ACM, CG, DT and DZ acknowledge funding through the German Research Council (DFG), grants no. MU 4603/1-1 (PAK997/1). MM acknowledges funding through the German Research Council (DFG), grants no. ZI 736/2-1. All other authors do not declare financial interests/personal relationships.

Figures

Fig. 1
Fig. 1
Schematic illustration of (a) the refPlan including pCT, contours and dose distribution, (b) conv-IGRT simulation with rigid registration of the pCT to each T2w-MRI and the resulting translation matrix T, and (c) OA-MRgRT with new online adaptive dose planning for each fraction.
Fig. 2
Fig. 2
Schematic overview of a) the DIR and b) DDA procedure for conv-IGRT and OA-MRgRT. The DIR resulted in a DVF used for dose mapping for both accumulation approaches rigid registered refPlan doses of conv-IGRT and the daily adaptive doses of OA-MRgRT.
Fig. 3
Fig. 3
Boxplots showing the differences in the DVPs for CTV and OARs between refPlan, conv-IGRT, and OA-MRgRT. The boxes represent interquartile range (IQR), which is the range between the first quartile (Q1) and the third quartile (Q3). The black line inside the box is the median of the dataset. The length of the whiskers is set to 1.5 times the IQR. Individual data points beyond the whiskers are considered potential outliers and plotted as black circles. The color-coded points are the patient-individual results. The red dotted lines represent the planning objectives: CTV D50%≥60 Gy (a), D98%≥57 Gy (b), rectum, bladder, and urethra Dmax < 61 Gy (c, e, g), rectum V56Gy < 13.5 % (d), and bladder V56Gy < 18 % (f). Statistical analysis was performed using the non-parametric Wilcoxon signed-rank test, with α = 0.05 and Bonferroni correction accounting for the three different treatment approaches, in addition to Cohen's d.
Fig. 4
Fig. 4
Illustration of the mean DVHs results across all patients for refPlan (red), conv-IGRT (green) and OA-MRgRT (blue) in the CTV (a), rectum (b), bladder (c), and urethra (d). The transparent area for each approach represents the standard deviation across all patients.
Fig. 5
Fig. 5
Sagittal view of the refPlan and the different accumulated dose distribution results, conv-IGRT and OA-MRgRT, for patient 10. The contours of CTV, rectum, and bladder are shown.
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