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. 2019 Mar 6:9:69-76.
doi: 10.1016/j.phro.2019.02.002. eCollection 2019 Jan.

Clinical implementation of magnetic resonance imaging guided adaptive radiotherapy for localized prostate cancer

Shyama U Tetar  1 , Anna M E Bruynzeel  1 , Frank J Lagerwaard  1 , Ben J Slotman  1 , Omar Bohoudi  1 , Miguel A Palacios  1
Affiliations

Clinical implementation of magnetic resonance imaging guided adaptive radiotherapy for localized prostate cancer

Shyama U Tetar et al. Phys Imaging Radiat Oncol. .

Abstract

Background and purpose: Magnetic resonance-guided radiation therapy (MRgRT) has recently become available in clinical practice and is expected to expand significantly in coming years. MRgRT offers marker-less continuous imaging during treatment delivery, use of small clinical target volume (CTV) to planning target volume (PTV) margins, and finally the option to perform daily plan re-optimization.

Materials and methods: A total of 140 patients (700 fractions) have been treated with MRgRT and online plan adaptation for localized prostate cancer since early 2016. Clinical workflow for MRgRT of prostate cancer consisted of patient selection, simulation on both MR- and computed tomography (CT) scan, inverse intensity-modulated radiotherapy (IMRT) treatment planning and daily plan re-optimization prior to treatment delivery with partial organs at risk (OAR) recontouring within the first 2 cm outside the PTV. For each adapted plan online patient-specific quality assurance (QA) was performed by means of a secondary Monte Carlo 3D dose calculation and gamma analysis comparison. Patient experiences with MRgRT were assessed using a patient-reported outcome questionnaire (PRO-Q) after the last fraction.

Results: In 97% of fractions, MRgRT was delivered using the online adapted plan. Intrafractional prostate drifts necessitated 2D-corrections during treatment in approximately 20% of fractions. The average duration of an uneventful fraction of MRgRT was 45 min. PRO-Q's (N = 89) showed that MRgRT was generally well tolerated, with disturbing noise sensations being most commonly reported.

Conclusions: MRgRT with daily online plan adaptation constitutes an innovative approach for delivering SBRT for prostate cancer and appears to be feasible, although necessitating extended timeslots and logistical challenges.

Keywords: MR-guided Radiotherapy (MRgRT); On-table adaptation; Prostate cancer; Stereotactic body radiotherapy (SBRT); Workflow.

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Figures

Fig. 1
Fig. 1
Contouring for MRgRT: CTV consisting of prostate and base of vesicles (green contour), PTV (CTV + 3 mm; red contour) visualized in an axial, sagittal and coronal plane. The urethral contour (cyan contour) and urethral PRV (urethra + 2 mm) can be best seen in the sagittal plane. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 2
Fig. 2
Workflow for MRgRT with online plan adaptation for prostate cancer. HR = high resolution, MR = magnetic resonance, CTV = clinical target volume, OAR = organs at risk, QA = quality assurance.
Fig. 3
Fig. 3
Treatment plan at baseline (top row), predicted plan (middle row) and adapted plan (bottom row) at one particular fraction. Objectives and clinical constraints according to the institutional protocol for SBRT in prostate cancer can be seen on the right of the figure, where a comparison of the values achieved by the predicted and adapted plan is shown. Values which do not meet the preset values are highlighted in yellow. At the bottom of the figure, a DVH comparison of the three plans is shown. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 4
Fig. 4
Gated MRgRT delivery for prostate cancer. The gating target (CTV; green contour) and the gating boundary (red contour) are visualized on-screen. The geometric coverage (“Target out”) is continuously displayed in the left upper corner. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 5
Fig. 5
Patient-reported complaints during MRgRT for prostate cancer (N = 89).
See this image and copyright information in PMC

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