The first MRIdian® MR linear accelerator (MR-Linac; ViewRay, Oakwood Village, Ohio) in the United Kingdom went live in December 2019 following a record installation time. Stereotactic MRI-guided Adaptive Radiotherapy (SMART) has since been implemented and has advantages of excellent soft tissue definition of both target and organs at risk (OARs), real-time target and OAR visualisation on cine-MRI, daily recontouring of target and critical OARs with live online plan adaptation/re-optimisation, and automatic respiratory-gated treatment delivery. We present a multi-disciplinary narrative and technical description of how this innovative technique was implemented for hepatobiliary (HPB) cancers. In particular, we explain how a collaborative approach and desire to push the boundaries and improve outcomes enabled 50 patients to be treated in the first five months, many with technically challenging tumours not always deliverable on other platforms. Physics, dosimetry, radiographer, and clinician perspectives on implementing SMART are presented. MRIdian® single fraction lung stereotactic ablative radiotherapy (SABR) will shortly be implemented along with innovative research in conjunction with our academic partners.
Purpose: Image guided radiation therapy (IGRT) is becoming the standard of practice for many treatment sites. Our purpose in this study was to quantify the improvement in setup accuracy with the use of IGRT in TomoTherapy. We have analyzed shifts in the X,Y,Z directions for patients undergoing daily IGRT and treatment with a TomoTherapy Hi‐Art unit. Total vector shifts were also calculated. Four distinct patient groups were analyzed: cranial, head and neck, prostate with implanted fiducials, and prostatectomy patients. Method and Materials: Megavoltage computed tomography (MVCT) was carried out at each treatment fraction. The MVCT was fused to the planning KVCT and the resultant X,Y,Z offsets determined. A total of 1,303 X,Y,Z measurements from 48 patients were collected for this study. The data is presented separately for each of the four groups. Results: Prostate patients with implanted gold markers had the largest vector shifts with a mean of 9.0 mm. The magnitude of this vector was largely due to vertical shifts (Z direction) with a mean of 7.1 mm. Prostatectomy patients were set up based on bone fusion and had an average vector shift of 7.8 mm, while head and neck and cranial patients had an average shift of 5.0 mm and 4.7 mm respectively. Data for the displacement in each of the X,Y,Z directions is also presented. The variation in shifts between different patients within a group was significant and varied by at least a factor of four. Conclusion: This study demonstrates quantitatively the potential improvement in radiotherapy accuracy with the use of IGRT in TomoTherapy. Corrections in setup in the Z (vertical) direction account for the largest contribution to the vectors calculated. The use of extremely high dose gradients in IMRT has made patient positioning accuracy even more critical than in previous modalities.
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