Abstract

Title

Online adaptive MR-guided SBRT for unresectable upper abdominal malignancies using a 1.5T MR-linac

Authors

Lois Daamen1, Sophie de Mol van Otterloo2, Iris van Goor2, Hidde Eijkelenkamp2, Beth Erickson3, William Hall3, Hanne Heerkens2, Gert Meijer2, Quintus Molenaar4, Hjalmar van Santvoort4, Lenny Verkooijen1, Martijn Intven2

Authors Affiliations

1UMC Utrecht, Imaging Division, Utrecht, The Netherlands; 2UMC Utrecht, Radiotherapy, Utrecht, The Netherlands; 3Medical College of Wisconsin, Radiotherapy, Milwaukee, WI, USA; 4Regional Academic Cancer Center Utrecht, Surgery, Utrecht, The Netherlands

Purpose or Objective

The introduction of online adaptive MR-guided radiotherapy enables stereotactic body radiation therapy (SBRT) of upper abdominal tumors. The aim of this study was to evaluate the feasibility of MR-guided SBRT on a 1.5T MR-linac in a first group of patients with unresectable malignancies in the upper abdomen.

Materials and Methods

Patients with unresectable, pathology-proven upper abdominal malignancies who were treated at the UMC Utrecht (April 2019-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 of ≤60 minutes for >75% of delivered fractions and successful completion of >95% of fractions as scheduled. Treatment-related toxicity and tumor stability on CT-imaging were assessed.

Results

Twenty-five consecutive patients with a median follow-up time of 7 (range 1 to 20) months were treated with 35 Gray (n=4) and 40 Gray (n=21) in five fractions over two weeks. For all fractions, contours were adapted based on the daily anatomy of the tumor and organs-at-risk and delivered within a median on-table time of 47 minutes/fraction (range 30-74). In 98/117 fractions (84%), adapted treatment was completed within one hour. All patients received the scheduled irradiation dose as planned. No acute grade 3 toxicity or higher was reported. Tumor stability is shown in figure 1.




Conclusion

Online adaptive MR-guided SBRT on a 1.5T MR-linac is feasible in patients with unresectable malignancies in the upper abdomen. Dose escalation studies, followed by comparative studies, are needed to determine the optimal radiation dose needed.