MR‐Linac Successfully Guided the Treatment of a Free‐Moving Mesenteric Mass

Abstract A patient presenting with stage I follicular lymphoma was dispositioned for a definitive and curative radiation treatment. The tumor had significant daily movement, as much as 3.83, 3.26 and 12.42 cm in the anterior‐posterior, superior‐inferior and left‐right direction respectively. The tumor volume increased from 16.72 to 44.23 cc in first 5 fractions, followed by a downward trend. To account for the inter‐fraction tumor motion, online adaptive radiation therapy was delivered using Elekta Unity MR‐Linac. Each fraction, the treating physician manually delineated the planning target volume (PTV) and Unity successfully generated an optimum adaptive plan with PTV coverage ≥ 95%. This case demonstrated that MR‐Linac online adaptive workflow was superior in treating a free‐moving and volume changing mesenteric mass, minimizing the margin needed in conventional static plan to cover the unpredictable large daily shift.