Quantifying the reduction of respiratory motion by mechanical ventilation with MRI for radiotherapy

Abstract

Background Due to respiratory motion, accurate radiotherapy delivery to thoracic and abdominal tumors is challenging. We aimed to quantify the ability of mechanical ventilation to reduce respiratory motion, by measuring diaphragm motion magnitudes in the same volunteers during free breathing (FB), mechanically regularized breathing (RB) at 22 breaths per minute (brpm), variation in mean diaphragm position across multiple deep inspiration breath-holds (DIBH) and diaphragm drift during single prolonged breath-holds (PBH) in two MRI sessions. Methods In two sessions, MRIs were acquired from fifteen healthy volunteers who were trained to be mechanically ventilated non-invasively We measured diaphragm motion amplitudes during FB and RB, the inter-quartile range (IQR) of the variation in average diaphragm position from one measurement over five consecutive DIBHs, and diaphragm cranial drift velocities during single PBHs from inhalation (PIBH) and exhalation (PEBH) breath-holds. Results RB significantly reduced the respiratory motion amplitude by 39%, from median (range) 20.9 (10.6–41.9) mm during FB to 12.8 (6.2–23.8) mm. The median IQR for variation in average diaphragm position over multiple DIBHs was 4.2 (1.0–23.6) mm. During single PIBHs with a median duration of 7.1 (2.0–11.1) minutes, the median diaphragm cranial drift velocity was 3.0 (0.4–6.5) mm/minute. For PEBH, the median duration was 5.8 (1.8–10.2) minutes with 4.4 (1.8–15.1) mm/minute diaphragm drift velocity. Conclusions Regularized breathing at a frequency of 22 brpm resulted in significantly smaller diaphragm motion amplitudes compared to free breathing. This would enable smaller treatment volumes in radiotherapy. Furthermore, prolonged breath-holding from inhalation and exhalation with median durations of six to seven minutes are feasible. Trial registration Medical Ethics Committee protocol NL.64693.018.18.

Accuracy of abdominal organ motion estimation in radiotherapy using the right hemidiaphragm top as a surrogate during prolonged breath‐holds quantified with MRI

“…To do this safely and comfortably, subjects are trained. Training procedures have been described previously by van Kesteren et al 17 All volunteers were trained in two sessions to be ventilated through a facemask connected to a Hamilton MR1 mechanical ventilator (Hamilton Medical AG, Bonaduz, Switzerland). This enabled mechanical hyperventilation with 60% O 2 to reduce the end-tidal partial pressure of CO 2 to 20 mmHg inducing a state of hypocapnia, after which volunteers performed a PBH from end-inspiration for as long as they could.…”

“…During each PBH, 3D cine-MRIs were acquired on a 3T MRI (Ingenia, Philips Healthcare) using a fast balanced turbo field echo (BTFE) sequence with a FOV including the lung tops and both kidneys ( accurately quantify organ motion during PBH given the median 3 mm/min drift of the RHT. 17 We then determined organ displacements by: (1) generation of DVFs using DIR on a selection of dynamics, (2) segmentation of regions-of -interest (ROI), and (3) calculation of ROI displacements using the DVFs.…”

“…14 Using prolonged breath-holds (PBH) with durations of >5 min to study the diaphragm as surrogate for abdominal organ motion avoids the disadvantages of FB and the short duration of DIBH. First, the organ motion velocity is low 17 and phase differences should be negligible. Secondly, more accurate analysis is possible due to the longer duration of a PBH, during which abdominal organ displacements are larger.…”

“…Secondly, more accurate analysis is possible due to the longer duration of a PBH, during which abdominal organ displacements are larger. 17 Thirdly, the low motion velocity allows for large field-of -view (FOV) 3dimensional MRI with minimal motion artefacts,enabling detailed analyses on motion of organs within a large FOV.For these analyses,deformation vector fields (DVF) generated by deformable image registration (DIR) have shown great potential in previous studies analyzing motion patterns. [18][19][20][21] The aim of this study was to quantify the error when using the right hemidiaphragm top (RHT) as surrogate for abdominal organ motion during PBH for possible application during radiation treatments.…”

Correction: Quantifying the reduction of respiratory motion by mechanical ventilation with MRI for radiotherapy

“…After publication of this article [ 1 ], the authors reported that a wrong figure appeared as Fig. 5 ; the figure should have appeared as shown below.…”