Figure 1.

MR-guided adaptive radiation therapy. Seventy-two-year-old female with three liver metastases (2 cm lesion in segment 8 and segments 3/4B measuring 1.6 cm) treated using MRg-ART on Elekta Unity MR-linac to a prescription of 60 Gy (12 Gy in 5 fractions). (A) The tumor metastasis was not visible on non-contrast planning CT as the patient was not a candidate for iodinated IV contrast due to poor renal function. Patient was simulated supine in a custom immobilization device and with an abdominal compression belt to minimize respiratory liver motion to <5 mm. (B) Online adaptive plan for a fraction on a T2 3D navigator triggered MRI. (C) T1w 3D fat saturated MRI was used in combination with T2 3D navigator triggered sequence to delineate GTV and OARs during online planning. Daily adaptive planning was performed to account for coverage of multiple lesions (due to varying deformations in the liver) as well as to protect the organs at risk. Bile ducts were used as the monitoring structure on the three orthogonal plane balanced fast field echo cine MRI during radiation delivery. (D) Daily dosimetric coverage for GTV and various relevant OARs. Each fraction dose is displayed in terms total prescription dose.