“Online Correction of Intrafraction Motion during Volumetric Modulated Arc Therapy for Prostate Radiotherapy: A Cohort Study Quantifying the Frequency of Shifts and Analysis of Men at Highest Risk”
Methods (extract): 132 prostate cancer patients underwent planning CT and same day placement of 3 Gold Anchor markers. Triggered kV images were acquired every 10 seconds using the Varian TrueBeam onboard imaging system. Intrafraction motion correction was considered if any two fiducial markers were observed beyond a 3 mm tolerance margin. Shift percent was defined as the number of instances of a >3 mm intrafraction correction divided by the total number of fractions for a given patient.
Results (extract): Across 2659 fractions, intrafraction motion correction was performed 582 times, in 463 fractions (17%). 101/132 patients (77%) had at least one shift during their treatment course, and 48/132 patients (36%) had shifts with an average magnitude of at least 5 mm. The median shift was 3.6 mm. 25% of men had a shift percent >20%.
Conclusion (extract): Intrafraction motion occurs in a significant percentage of men undergoing prostate RT with VMAT, and is correctable utilizing a common feature. Treatment approaches which do not account for intrafraction motion should consider including methods of immobilization, or larger PTV margins in order to avoid marginal miss of the prostate.