Dedicated magnetic resonance imaging in the radiotherapy clinic.
OBJECTIVE
To introduce a novel technology arrangement in an integrated environment and outline the logistics model needed to incorporate dedicated magnetic resonance (MR) imaging in the radiotherapy workflow. An initial attempt was made to analyze the value and feasibility of MR-only imaging compared to computed tomography (CT) imaging, testing the assumption that MR is a better choice for target and healthy tissue delineation in radiotherapy.


METHODS
A 1.5-T MR unit with a 70-cm-bore size was installed close to a linear accelerator, and a special trolley was developed for transporting patients who were fixated in advance between the MR unit and the accelerator. New MR-based workflow procedures were developed and evaluated.


RESULTS
MR-only treatment planning has been facilitated, thus avoiding all registration errors between CT and MR scans, but several new aspects of MR imaging must be considered. Electron density information must be obtained by other methods. Generation of digitally reconstructed radiographs (DRR) for x-ray setup verification is not straight forward, and reliable corrections of geometrical distortions must be applied. The feasibility of MR imaging virtual simulation has been demonstrated, but a key challenge to overcome is correct determination of the skeleton, which is often needed for the traditional approach of beam modeling. The trolley solution allows for a highly precise setup for soft tissue tumors without the invasive handling of radiopaque markers.


CONCLUSIONS
The new logistics model with an integrated MR unit is efficient and will allow for improved tumor definition and geometrical precision without a significant loss of dosimetric accuracy. The most significant development needed is improved bone imaging.
Department of Radiation Sciences, Umeå University, Sweden. Mikael.Karlsson@radfys.umu.se
Mikael
M
Karlsson
Magnus G
MG
Karlsson
Tufve
T
Nyholm
Christopher
C
Amies
Björn
B
Zackrisson
D000465:Algorithms; D001842:Bone and Bones / Q000033:anatomy & histology; D005240:Feasibility Studies; D006801:Humans; D007103:Immobilization / Q000379:methods; D016015:Logistic Models; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009369:Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D010315:Particle Accelerators; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012983:Soft Tissue Neoplasms / Q000473:pathology / Q000532:radiotherapy; D014057:Tomography, X-Ray Computed; D014187:Transportation of Patients