Online adaptive MR-guided stereotactic radiotherapy for unresectable malignancies in the upper abdomen using a 1.5T MR-linac.
BACKGROUND
Introduction of online adaptive MR-guided radiotherapy enables stereotactic body radiation therapy (SBRT) of upper abdominal tumors. This study aimed to evaluate the feasibility of MR-guided SBRT on a 1.5 T MR-linac in patients with unresectable upper abdominal malignancies.


MATERIAL AND METHODS
Patients treated at the UMC Utrecht (April 2019 to December 2020) were identified in the prospective 'Multi-OutcoMe EvaluatioN of radiation Therapy Using the MR-linac' (MOMENTUM) study. Feasibility of treatment was arbitrarily defined as an on-table time interval of ≤60 min for >75% of delivered fractions and completion of >95% of fractions as scheduled, reflecting patient tolerability. Acute treatment-related toxicity was assessed at 3 months of follow-up and graded according to the National Cancer Institute Common Terminology Criteria of Adverse Events version 5.0.


RESULTS
Twenty-five consecutive patients with a median follow-up time of 8 (range 4-23) months were treated with 35 Gray (n = 4) and 40 Gray (n = 21) in five fractions over 2 weeks. For all fractions, contours were adapted based on the daily anatomy and delivered within 47 min/fraction (range 30-74). In 98/117 fractions (84%), adapted treatment was completed within 1 h. All patients received the scheduled irradiation dose as planned. No acute grade 3 toxicity or higher was reported. Treatment resulted in pain alleviation in 11/13 patients.


DISCUSSION
Online adaptive MR-guided SBRT on a 1.5 T MR-linac is feasible and well-tolerated in patients with unresectable upper abdominal malignancies. Dose escalation studies, followed by comparative studies, are needed to determine the optimal radiation dose for irradiation of upper abdominal malignancies.
['Daamen|Lois A|LA|', 'de Mol van Otterloo|Sophie R|SR|', 'van Goor|Iris W J M|IWJM|', 'Eijkelenkamp|Hidde|H|', 'Erickson|Beth A|BA|', 'Hall|William A|WA|', 'Heerkens|Hanne D|HD|', 'Meijer|Gert J|GJ|', 'Molenaar|I Quintus|IQ|', 'van Santvoort|Hjalmar C|HC|', 'Verkooijen|Helena M|HM|0000-0001-9480-1623', 'Intven|Martijn P W|MPW|0000-0002-5068-5517']
MR-linac MR-guided radiotherapy stereotactic body radiation therapy upper abdominal malignancies radiation oncology