Clinical Implementational and Site-Specific Workflows for a 1.5T MR-Linac

Abstract

MR-guided adaptive radiotherapy (MRgART) provides opportunities to benefit patients through enhanced use of advanced imaging during treatment for many patients with various cancer treatment sites. This novel technology presents many new challenges which vary based on anatomic treatment location, technique, and potential changes of both tumor and normal tissue during treatment. When introducing new treatment sites, considerations regarding appropriate patient selection, treatment planning, immobilization, and plan-adaption criteria must be thoroughly explored to ensure adequate treatments are performed. This paper presents an institution’s experience in developing a MRgART program for a 1.5T MR-linac for the first 234 patients. The paper suggests practical treatment workflows and considerations for treating with MRgART at different anatomical sites, including imaging guidelines, patient immobilization, adaptive workflows, and utilization of bolus.

A pilot study of same-day MRI-only simulation and treatment with MR-guided adaptive palliative radiotherapy (MAP-RT)

“…Follow-up was intentionally limited as the purpose of the study was to establish proof of principle for a novel workflow with early toxicity assessment in a patient population with historically poor prognosis. While other MRgRT treatment platforms are available [31] , they are at different points of development and capability to offer gated treatments of mobile targets. Notwithstanding these considerations, these data indicate that same day MRI-only simulation and treatment with MAP-RT was feasible with a reasonable toxicity profile.…”

Intra-fraction motion of pelvic oligometastases and feasibility of PTV margin reduction using MRI guided adaptive radiotherapy

“…The study was conducted in accordance with the International Council for Harmonization ICH E6(R2) Good Clinical Practice as adopted by the United States FDA, which aligns with the principles of Helsinki. All patients enrolled in this study had a GTV which was well visualized on a balanced fast field echo (TE 3.8 ms, TR 1.92 ms, flip angle: 40 degrees) cine MRI imaging sequence which comes standard on the Unity system ( 32 ).…”

“…The GTV was expanded uniformly by 2mm, 3mm, and 5mm respectively to create the PTV in each plan. A nine-field step-and-shoot IMRT beam arrangement which avoided the cryostat pipe was used for planning ( 9 , 32 ). Each PTV margin plan was created using a maximum of 10 segment shape optimization loops and IMRT parameters were held constant for each plan.…”

“…In the clinical setting, the Hyperion optimizer in the Monaco TPS was used to generate a fully adapted plan starting from fluence ( 34 ). Following the completion of the adapted plan, online quality assurance procedures were performed and MRI cine motion monitoring images were acquired throughout the duration of treatment ( 32 ).…”

MRI-Guided Radiotherapy for Prostate Cancer: a New Paradigm

“…The typical clinical workflow with hybrid MRgRT machine still involves pretreatment CT imaging on separate CT simulator which is registered with daily MRI taken on MRI-linac (14). The illustration of the paradigm change introduced by MRgRT in the radiotherapy workflow, enabling real time adaptive radiotherapy, is presented in the Fig.…”