MRI/linac integration.
OBJECTIVE
In radiotherapy the healthy tissue involvement still poses serious dose limitations. This results in sub-optimal tumour dose and complications. Daily image guided radiotherapy (IGRT) is the key development in radiation oncology to solve this problem. MRI yields superb soft-tissue visualization and provides several imaging modalities for identification of movements, function and physiology. Integrating MRI functionality with an accelerator can make these capacities available for high precision, real time IGRT.


RESULTS
The system being built at the University Medical Center Utrecht is a 1.5T MRI scanner, with diagnostic imaging functionality and quality, integrated with a 6MV radiotherapy accelerator. The realization of a prototype of this hybrid system is a joint effort between the Radiotherapy Department of the University of Utrecht, the Netherlands, Elekta, Crawley, U.K., and Philips Research, Hamburg, Germany. Basically, the design is a 1.5 T Philips Achieva MRI scanner with a Magnex closed bore magnet surrounded by a single energy (6 MV) Elekta accelerator. Monte Carlo simulations are used to investigate the radiation beam properties of the hybrid system, dosimetry equipment and for the construction of patient specific dose deposition kernels in the presence of a magnetic field. The latter are used to evaluate the IMRT capability of the integrated MRI linac.


CONCLUSIONS
A prototype hybrid MRI/linac for on-line MRI guidance of radiotherapy (MRIgRT) is under construction. The aim of the system is to deliver the radiation dose with mm precision based on diagnostic quality MR images.
Lagendijk
Jan J W
JJ
Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan, The Netherlands. J.J.W.Lagendijk@umcutrecht.nl
Raaymakers
Bas W
BW
Raaijmakers
Alexander J E
AJ
Overweg
Johan
J
Brown
Kevin J
KJ
Kerkhof
Ellen M
EM
van der Put
Richard W
RW
Hårdemark
Björn
B
van Vulpen
Marco
M
van der Heide
Uulke A
UA
D006801:Humans; D008279:Magnetic Resonance Imaging; D010315:Particle Accelerators / Q000295:instrumentation; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted