MR-guidance – a clinical study to evaluate a shuttle- based MR-linac connection to provide MR-guided radiotherapy

Abstract

BackgroundThe purpose of this clinical study is to investigate the clinical feasibility and safety of a shuttle-based MR-linac connection to provide MR-guided radiotherapy.Methods/DesignA total of 40 patients with an indication for a neoadjuvant, adjuvant or definitive radiation treatment will be recruited including tumors of the head and neck region, thorax, upper gastrointestinal tract and pelvic region. All study patients will receive standard therapy, i.e. highly conformal radiation techniques like CT-guided intensity-modulated radiotherapy (IMRT) with or without concomitant chemotherapy or other antitumor medication, and additionally daily short MR scans in treatment position with the same immobilisation equipment used for irradiation for position verification and imaging of the anatomical and functional changes during the course of radiotherapy. For daily position control, skin marks and a stereotactic frame will be used for both imaging modalities. Patient transfer between the MR device and the linear accelerator will be performed with a shuttle system which uses an air-bearing patient platform for both procedures. The daily acquired MR and CT data sets will be digitally registrated, correlated with the planning CT and compared with each other regarding translational and rotational errors. Aim of this clinical study is to establish a shuttle-based approach for realising MR-guided radiotherapy for certain clinical situations. Second objectives are to compare MR-guided radiotherapy with the gold standard of CT image guidance for quality assurance of radiotherapy, to establish an appropiate MR protocol therefore, and to assess the possibility of using MR-based image guidance not only for position verification but also for adaptive strategies in radiotherapy.DiscussionCompared to CT, MRI might offer the advantage of providing IGRT without delivering an additional radiation dose to the patients and the possibility of optimisation of adaptive therapy strategies due to its superior soft tissue contrast. However, up to now, hybrid MR-linac devices are still under construction and not clinically applicable. For the near future, a shuttle-based approach would be a promising alternative for providing MR-guided radiotherapy, so that the present study was initiated to determine feasibility and safety of such an approach. Besides positioning information, daily MR data under treatment offer the possibility to assess tumor regression and functional parameters, with a potential impact not only on adaptive therapy strategies but also on early assessment of treatment response.

Review of potential improvements using MRI in the radiotherapy workflow

“…In addition, this trolley solution provides a highly precise setup for soft tissue tumors without the invasive nature of using radioopaque markers. Another group has recently confirmed the feasibility of this approach in a clinical environment [58].…”

What will the medical physics of proton therapy look like 10 yr from now? A personal view

“…On the other hand, there could be a potential for this approach for single room facilities, 16 where the accelerator is dedicated to a single treatment chamber, or as a simpler solution to MR guided proton therapy, with the MRI imaging being performed outside of the treatment room immediately before treatment. 18 In this case, I believe that the concept of out-of-room patient setup and imaging may be worth re-visiting. If accurate, efficient and comfortable patient transporters could be developed, then significant potential gains in patient throughput could be achieved for the single room scenario.…”

“…Indeed, this “dead‐time” increases with the number of treatment rooms fed by a single accelerator, meaning that out‐of‐room setup and imaging probably has little advantage for multiple‐room facilities. On the other hand, there could be a potential for this approach for single room facilities, where the accelerator is dedicated to a single treatment chamber, or as a simpler solution to MR guided proton therapy, with the MRI imaging being performed outside of the treatment room immediately before treatment . In this case, I believe that the concept of out‐of‐room patient setup and imaging may be worth re‐visiting.…”

Feasibility of MRI-only treatment planning for proton therapy in brain and prostate cancers: Dose calculation accuracy in substitute CT images

“…[5][6][7][8][9][10]12,14,15,17,18 Clinical interest in MRI localization-based IGRT has been growing in recent years due to developments in MRI-guided radiotherapy, such as MR-linacs, MR-on-rails, and table-trolley systems. [20][21][22][23][24] Volumetric MR studies are also increasingly utilized for posttreatment monitoring. [25][26][27] High quality soft-tissue visualization in MRI assists target delineation and image guidance needed for intensity modulated proton therapy (IMPT) to realize its maximum clinical potential for avoiding radiation toxicity.…”