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. 2023 Dec 20:13:1337626.
doi: 10.3389/fonc.2023.1337626. eCollection 2023.

Optimal planning target margin for prostate radiotherapy based on interfractional and intrafractional variability assessment during 1.5T MRI-guided radiotherapy

Jina Kim  1 , Jiwon Sung  1 , Seo Jin Lee  1 , Kang Su Cho  2 , Byung Ha Chung  2 , Dongjoon Yang  1 , Jihun Kim  1 , Jun Won Kim  1
Affiliations

Optimal planning target margin for prostate radiotherapy based on interfractional and intrafractional variability assessment during 1.5T MRI-guided radiotherapy

Jina Kim et al. Front Oncol. .

Abstract

Introduction: We analyzed daily pre-treatment- (PRE) and real-time motion monitoring- (MM) MRI scans of patients receiving definitive prostate radiotherapy (RT) with 1.5 T MRI guidance to assess interfractional and intrafractional variability of the prostate and suggest optimal planning target volume (PTV) margin.

Materials and methods: Rigid registration between PRE-MRI and planning CT images based on the pelvic bone and prostate anatomy were performed. Interfractional setup margin (SM) and interobserver variability (IO) were assessed by comparing the centroid values of prostate contours delineated on PRE-MRIs. MM-MRIs were used for internal margin (IM) assessment, and PTV margin was calculated using the van Herk formula.

Results: We delineated 400 prostate contours on PRE-MRI images. SM was 0.57 ± 0.42, 2.45 ± 1.98, and 2.28 ± 2.08 mm in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions, respectively, after bone localization and 0.76 ± 0.57, 1.89 ± 1.60, and 2.02 ± 1.79 mm in the LR, AP, and SI directions, respectively, after prostate localization. IO was 1.06 ± 0.58, 2.32 ± 1.08, and 3.30 ± 1.85 mm in the LR, AP, and SI directions, respectively, after bone localization and 1.11 ± 0.55, 2.13 ± 1.07, and 3.53 ± 1.65 mm in the LR, AP, and SI directions, respectively, after prostate localization. Average IM was 2.12 ± 0.86, 2.24 ± 1.07, and 2.84 ± 0.88 mm in the LR, AP, and SI directions, respectively. Calculated PTV margin was 2.21, 5.16, and 5.40 mm in the LR, AP, and SI directions, respectively.

Conclusions: Movements in the SI direction were the largest source of variability in definitive prostate RT, and interobserver variability was a non-negligible source of margin. The optimal PTV margin should also consider the internal margin.

Keywords: MRI-guided radiotherapy; PTV margin; interfractional setup margin; interobserver variability; intrafractional motion; prostate cancer.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Workflow of MR-guided radiotherapy.
Figure 2
Figure 2
(A) Interfractional variability based on bone anatomy and prostate registration. (B) A case of maximum interfractional variability.
Figure 3
Figure 3
Correlation between bone- and prostate-based image registration in LR, AP, and SI directions.
Figure 4
Figure 4
(A) Interobserver variability based on bone anatomy and prostate registration. (B) A case of maximum interobserver variability.
See this image and copyright information in PMC

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