TY - JOUR
T1 - Bowel tracking for MR-guided radiotherapy
T2 - simultaneous optimization of small bowel imaging and tracking
AU - Damen, S.L.C.
AU - van Lier, A.L.H.M.W.
AU - Zachiu, C.
AU - Raaymakers, B.W.
N1 - Publisher Copyright:
© 2025 The Author(s). Published on behalf of Institute of Physics and Engineering in Medicine by IOP Publishing Ltd.
PY - 2025/4/6
Y1 - 2025/4/6
N2 - Objective. The small bowel is one of the most radiosensitive organs-at-risk during radiotherapy in the pelvis. This is further complicated due to anatomical and physiological motion. Thus, its accurate tracking becomes of particular importance during therapy delivery, to obtain better dose-toxicity relations and/or to perform safe adaptive treatments. The aim of this work is to simultaneously optimize the MR imaging sequence and motion estimation solution towards improved small bowel tracking precision during radiotherapy delivery. Approach. An MRI sequence was optimized, to adhere to the respiratory and peristaltic motion frequencies, by assesing the performance of an image registration algorithm on data acquired on volunteers and patients. In terms of tracking, three registration algorithms, previously-employed in the scope of image-guided radiotherapy, were investigated and optimized. The optimized scan was acquired for 7.5 min, in 18 patients and for 15 min, in 10 volunteers at a 1.5 T MRL (Unity, Elekta AB). The tracking precision was evaluated and validated by means of three different quality assurance criteria: Structural Similarity Index Measure (SSIM), Inverse Consistency (IC) and Absolute Intensity Difference. Main results. The optimal sequence was a balanced Fast Field Echo, which acquired a 3D volume of the abdomen, with a dynamic scan time of 1.8 s. An optical flow algorithm performed best and which was able to resolve most of the motion. This was shown by mean IC values of < 1 mm and a mean SSIM > 0.9 for the majority of the cases. A strong positive correlation (p < 0.001) between the registration performance and visceral fat percentage was found, where a higher visceral fat percentage gave a better registration due to the better image contrast. Significance. A method for simultaneous optimization of imaging and tracking was presented, which derived an imaging and registration procedure for accurate small bowel tracking on the MR-Linac.
AB - Objective. The small bowel is one of the most radiosensitive organs-at-risk during radiotherapy in the pelvis. This is further complicated due to anatomical and physiological motion. Thus, its accurate tracking becomes of particular importance during therapy delivery, to obtain better dose-toxicity relations and/or to perform safe adaptive treatments. The aim of this work is to simultaneously optimize the MR imaging sequence and motion estimation solution towards improved small bowel tracking precision during radiotherapy delivery. Approach. An MRI sequence was optimized, to adhere to the respiratory and peristaltic motion frequencies, by assesing the performance of an image registration algorithm on data acquired on volunteers and patients. In terms of tracking, three registration algorithms, previously-employed in the scope of image-guided radiotherapy, were investigated and optimized. The optimized scan was acquired for 7.5 min, in 18 patients and for 15 min, in 10 volunteers at a 1.5 T MRL (Unity, Elekta AB). The tracking precision was evaluated and validated by means of three different quality assurance criteria: Structural Similarity Index Measure (SSIM), Inverse Consistency (IC) and Absolute Intensity Difference. Main results. The optimal sequence was a balanced Fast Field Echo, which acquired a 3D volume of the abdomen, with a dynamic scan time of 1.8 s. An optical flow algorithm performed best and which was able to resolve most of the motion. This was shown by mean IC values of < 1 mm and a mean SSIM > 0.9 for the majority of the cases. A strong positive correlation (p < 0.001) between the registration performance and visceral fat percentage was found, where a higher visceral fat percentage gave a better registration due to the better image contrast. Significance. A method for simultaneous optimization of imaging and tracking was presented, which derived an imaging and registration procedure for accurate small bowel tracking on the MR-Linac.
KW - deformable image registration
KW - MR-guided radiotherapy
KW - real-time tracking
KW - small bowel
UR - http://www.scopus.com/inward/record.url?scp=105000221252&partnerID=8YFLogxK
U2 - 10.1088/1361-6560/adbbac
DO - 10.1088/1361-6560/adbbac
M3 - Article
C2 - 40020314
AN - SCOPUS:105000221252
SN - 0031-9155
VL - 70
JO - Physics in medicine and biology
JF - Physics in medicine and biology
IS - 7
M1 - 075001
ER -