In September 2018 radiation oncologist Marlies Nowee treated the first patient on the MR-Linac. copyright Netherlands Cancer Institute.
The NKI is one of seven centres in the world that form a consortium for the clinical implementation of this revolutionary MR image guided treatment unit. In April 2016 the installation of an Elekta Unity MR-Linac started in the Netherlands Cancer Institute. The installation was finished in early 2017. For commissioning and clinical implementation a team of 14 physicians, 6 physicists, therapeutic radiographers and radiation physics engineers was formed, chaired by professor Uulke van der Heide (physicist, project leader) and Marlies Nowee (radiation oncologist).
fig.1 part of the MR-Linac team in the Netherlands Cancer Institute. copyright NKI
Adaptive Radiotherapy improved by MRI image guidance.
A 1,5 Tesla MRI-scanner and a linear accelerator with 7 MV photon beam are integrated into a compact treatment unit. The MRI scanner operates simultaneous with the accelerator and produces high quality images of the patient anatomy in which the alignment of the treatment and the effect of organ motion can be identified. This is especially advantageous in the treatment of moving tumours and tumours in soft tissue like in the prostate and rectum. MRI imaging gives a clear image of tumours and anatomy that cannot be imaged well with conventional X-Ray imaging. Treatment accuracy is improved, resulting in better sparing of surrounding healthy tissue and critical organs. The tumour can receive a higher radiation dose and the radiation course may be shortened for some patients. A certain group will be treated in five sessions instead of twenty.
Tumors in soft tissues
In the beginning the NKI will use the MR-Linac for the treatment of the prostate. More treatment techniques are being prepared for rectal cancer, head and neck tumours, lung, oesophagus, gynaecological tumors and mammae. It is expected that the MR-Linac will also offer advantage in the treatment of metastasis in the liver and some glands in the abdomen and the pelvic region.
During treatment the patient lies fixated on a treatment couch in the bore of the MR-Linac. The couch bed can only be adjusted longitudinally, other movements are impossible due to the restricted dimension of the bore. In case of geometric misalignment of the radiation beam, the multi leaf collimator is adjusted to restore the proper beam projection. In addition the shape of each radiation field and the dose weight factors may be adapted to the detected anatomical variations.
"On line adaptation" of the treatment plan.
fig.2 Online planning during treatment with the MR-Linac. Copyright University Medical Centre Utrecht.
The pre-treatment CT-scans on which the dose plan has been designed are compared to scans taken by the integrated MR during treatment. If necessary the pre-treatment CT scans are deformed to match with the MR-Linac scans. Pre-treatment contours are thus matched tot the actual situation during treatment. The treatment planning is redesigned, based on the deformed scan. After authorisation the redesigned plan is executed.
The "online adaptation" was estimated to last 15-30 minutes. In the beginning 45 minutes were planned for this, in practice it can be done in 30 minutes in many cases.
Global cooperation in the use of the MR-Linac.
A consortium of the industry and leading cancer centres has been formed for the clinical implementation of the MR-Linac. Consortium members are the manufacturers Elekta (Linac) and Philips (MRI) and 7 cancer centres where an MR-Linac has been installed as a clinical pilot system: the University Medical Centre in Utrecht (NL), the Netherlands Cancer Institute in Amsterdam (NL), Royal Marsden Hospital in London (VK), Christie hospital in Manchester ( VK), Froedtert/MCW in Wisconsin (USA), M D Anderson Cancer Centre in Houston (USA), en het Sunnybrook Odette Cancer Centre in Toronto (Can).
The consortium members are organised in tumour site groups, each group being coordinated by one of the participating members. Tumour groups at present are Rectum, Gynaecological, Prostate, Oesophagus, Lung, Mammae, and Head and Neck.
The NKI is coordinating the tumoursite group Rectum and is also participating in the implementation of the treatment of Lymph Nodes and Prostate. NKI is also coordinating the implementation of the treatment of Oligometastases and Liver metastases. Under consideration is a proposal for the treatment of Bladder and Stomach cancer.
More information on the MR-Linac can be found in websites by Elekta and Philips: