Variations of MRI-assessed peristaltic motions during radiation therapy

Abstract

Purpose: Understanding complex abdominal organ motion is essential for motion management in radiation therapy (RT) of abdominal tumors. This study investigates abdominal motion induced by respiration and peristalsis, during various time durations relevant to RT, using various CT and MRI techniques acquired under free breathing (FB) and breath hold (BH).

Methods: A series of CT and MRI images acquired with various techniques under free breathing and/or breath hold from 37 randomly-selected pancreatic or liver cancer patients were analyzed to assess the motion in various time frames. These data include FB 4DCT from 15 patients (for motion in time duration of 5 sec), FB 2D cine-MRI from 4 patients (time duration of 1.7 min, 1 second acquisition time per slice), FB cine-MRI acquired using MR-Linac from 6 patients in various fractions (acquisition time is less than 0.6 seconds per slice), FB 4DMRI from 2 patients (time duration of 2 min), respiration-gated T2 with gating at the end expiration (time duration of 3-5 min), and BH T1 with multiphase dynamic contrast in acquisition times of 17 seconds for each of five phases (pre-contrast, arterial, venous, portal venous and delayed post-contrast) from 10 patients. Motions of various organs including gallbladder (GB) and liver were measured based on these MRI data. The GB motion includes both respiration and peristalsis, while liver motion is primarily respiration. By subtracting liver motion (respiration) from GB motion (respiration and peristalsis), the peristaltic motion, along with small residual motion, was obtained.

Results: From cine-MRI, the residual motion beyond the respiratory motion was found to be up to 0.6 cm in superior-inferior (SI) and 0.55 cm in anterior-posterior (AP) directions. From 2D cine-MRI acquired by the MR-Linac, different peristaltic motions were found from different fractions for each patient. The peristaltic motion was found to vary between 0.3-1 cm. From BH T1 phase images, the average motions that were primarily due to peristalsis movements were found to be 1.2 cm in SI, 0.7 cm in AP, and 0.9 cm in left-right (LR) directions. The average motions assessed from 4DCT were 1.0 cm in SI and 0.3 cm in AP directions, which were generally smaller than the motions assessed from cine-MRI, i.e., 1.8 cm in SI and 0.6 cm in AP directions, for the same patients. However, average motions from 4DMRI, which are coming from respiratory were measured to be 1.5, 0.5, and 0.4 cm in SI, AP, and LR directions, respectively.

Conclusion: The abdominal motion due to peristalsis can be similar in magnitude to respiratory motion as assessed. These motions can be irregular and persistent throughout the imaging and RT delivery procedures, and should be considered together with respiratory motion during RT for abdominal tumors.

Fig 1. a) two contrast CT images of a patient with one min delay, b) two dual energy CT of the same patient with ~15 seconds delay.

Red: stomach, Blue: duodenum and Green: head of pancreas. The shape and direction of the duodenum changed between subsequent minute.

Fig 2. Liver, GB and kidney motions in 100 seconds using 2D cine-MRI in SI and AP directions.

Center of mass motions of liver and GB in both directions (left). Maximum and minimum motion of liver and GB due to respiratory (right).

Fig 3. Motion of GB (top) and liver (middle), and subtraction of GB motion from liver motion (bottom) in SI direction from 2D-cine MR.

Fig 4. The abdominal organ motion for one patient in the superior-inferior (SI), anterior-posterior (AP), and left-right (LR) directions from all T₁ phases with respect to T₂ weighted.

HP: head of pancreas, TP: tail of pancreas, duodenum, liver, and stomach.

Fig 5. The abdominal motions in the superior-inferior (SI), anterior-posterior (AP), and left-right (LR) directions analyzed from 4DMRI with respect to the 50% breathing phase.

HP: head of pancreas, TP: tail of pancreas, duodenum, liver, gallbladder and stomach.