Abstract
BackgroundIn radiotherapy, respiratory-induced tumor motion is typically measured using a single four-dimensional computed tomography acquisition (4DCT). Irregular breathing leads to inaccurate motion estimates, potentially resulting in undertreatment of the tumor and unnecessary dose to healthy tissue. The aim of the research was to determine if a daily pre-treatment 4DMRI-strategy led to a significantly improved motion estimate compared to single planning 4DMRI (with or without outlier rejection).Methods4DMRI data sets from 10 healthy volunteers were acquired. The first acquisition simulated a planning MRI, the respiratory motion estimate (constructed from the respiratory signal, i.e. the 1D navigator) was compared to the respiratory signal in the subsequent scans (simulating 5–29 treatment fractions). The same procedure was performed using the first acquisition of each day as an estimate for the subsequent acquisitions that day (2 per day, 4–20 per volunteer), simulating a daily MRI strategy. This was done for three outlier strategies: no outlier rejection (NoOR); excluding 5% of the respiratory signal whilst minimizing the range (Min95) and excluding the datapoints outside the mean end-inhalation and end-exhalation positions (MeanIE).ResultsThe planning MRI median motion estimates were 27 mm for NoOR, 18 mm for Min95, and 13 mm for MeanIE. The daily MRI median motion estimates were 29 mm for NoOR, 19 mm for Min95 and 15 mm for MeanIE. The percentage of time outside the motion estimate were for the planning MRI: 2%, 10% and 32% for NoOR, Min95 and MeanIE respectively. These values were reduced with the daily MRI strategy: 0%, 6% and 17%. Applying Min95 accounted for a 30% decrease in motion estimate compared to NoOR.ConclusionA daily MRI improved the estimation of respiratory motion as compared to a single 4D (planning) MRI significantly. Combining the Min95 technique with a daily 4DMRI resulted in a decrease of inclusion time of 6% with a 30% decrease of motion. Outlier rejection alone on a planning MRI often led to underestimation of the movement and could potentially lead to an underdosage.Trial registration: protocol W15_373#16.007
Highlights
Radiotherapy for upper abdominal cancer, such as pancreatic, esophageal and gastric cancer, is challenging due to poor contrast between tumor and other soft tissue on planning Computed tomography (CT) scans, as well as respiratory induced motion of both tumor and organs
Estimating the respiratory motion based on a single 4D acquisition leads to a large percentage of time that the motion during the simulated treatment fractions is outside the estimated motion, with or without outlier rejection; sessions were observed where this was the case 80% (MeanIE) and over 30% of the time (NoOR)
When the planning MRI strategy was compared to the daily MRI strategy, it was seen that the daily strategy performed significantly better for all three outlier rejection strategies, with better median values and smaller ranges for the time the simulated fractions were outside the motion estimates
Summary
Radiotherapy for upper abdominal cancer, such as pancreatic, esophageal and gastric cancer, is challenging due to poor contrast between tumor and other soft tissue on planning CT scans, as well as respiratory induced motion of both tumor and organs. The poor den Boer et al Radiat Oncol (2021) 16:188 soft-tissue contrast in the abdominal region on planning CT can be overcome by adding MRI images This decreases delineation variation [1,2,3,4,5,6] and is becoming common practice in the clinic [7]. Irregular breathing patterns during acquisition (e.g. caused by coughs or hiccups) can lead to image artefacts, both decreasing the image quality as well as the accuracy of the reconstructed respiratory motion. This motion may be overestimated which could potentially lead to the unnecessary exposure of healthy tissue or underestimated leading to insufficient tumor coverage. The aim of the research was to determine if a daily pre-treatment 4DMRI-strategy led to a significantly improved motion estimate compared to single planning 4DMRI (with or without outlier rejection)
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call