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

Abstract

A B S T R A C TBackground 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 intensitymodulated 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 patientreported 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. 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.

Impact of a vacuum cushion on intrafraction motion during online adaptive MR-guided SBRT for pelvic and para-aortic lymph node oligometastases

“…Nonetheless, with MRlinac plan adaptation based on the PV scan, only motion occurring after the PV scan would need to be taken into account for PTV margin calculation. Plan adaptation based on the PV scan is also possible on MRIdian treatment systems (ViewRay Inc., Oakwood, USA) [38]. In our study, we did not find a reduction in intrafraction motion using a vacuum cushion for the time interval between PV and post scan.…”

Assessing localized dosimetric effects due to unplanned gas cavities during pelvic MR‐guided radiotherapy using Monte Carlo simulations

“…13 However, as typical MRgRT workflows include daily imaging and a certain degree of adaptation of the original plan, the patient can be lying on the treatment coach for up to 30 min before treatment delivery. 14 During this time, gas or air is likely to appear in or pass through OARs, which would create deviations from the adapted dose distributions. In head and neck cancer patients, dosimetric effects due to ERE when the sinus cavity fills or clears have been shown to be of potential clinical concern.…”

Problems and Promises of Introducing the Magnetic Resonance Imaging Linear Accelerator Into Routine Care: The Case of Prostate Cancer

“…Our findings help radiation oncology departments determining focus areas in their strategy for successful MR-Linac implementation into prostate cancer care. Consistent with prior research, MR-Linac users expect to benefit from advanced MRI-guided radiation technology with online adaptive treatment and response assessment that may potentially improve patient outcomes and identify new treatment opportunities ( 7 , 8 , 10 , 19 , 40 ). The possibility of prostate hypofractionation promises improved treatment and economic benefits ( 17 , 20 , 41 – 43 ).…”