Clinical evaluation of 4D MRI in the delineation of gross and internal tumor volumes in comparison with 4DCT

Abstract

Purpose To evaluate clinical utility of respiratory‐correlated (RC) four‐dimensional magnetic resonance imaging (4DMRI) for lung tumor delineation and motion assessment, in comparison with the current clinical standard of 4D computed tomography (4DCT). Methods and Materials A prospective T2‐weighted (T2w) RC‐4DMRI technique was applied to acquire coronal 4DMRI images for 14 lung cancer patients (16 lesions) during free breathing (FB) under an IRB‐approved protocol, together with a breath‐hold (BH) T1w 3DMRI and axial 4DMRI. Clinical simulation CT and 4DCT were acquired within 2 h. An internal navigator was applied to trigger amplitude‐binned 4DMRI acquisition whereas a bellows or real‐time position management (RPM) was used in the 4DCT reconstruction. Six radiation oncologists manually delineated the gross and internal tumor volumes (GTV and ITV) in 399 3D images using programmed clinical workflows under a tumor delineation guideline. The ITV was the union of GTVs within the breathing cycle without margin. Average GTV and motion range were assessed and ITV variation between 4DMRI and 4DCT was evaluated using the Dice similarity index, mean distance agreement (MDA), and volume difference. Results The mean tumor volume is similar between 4DCT (GTV4DCT = 1.0, as the reference) and T2w‐4DMRI (GTVT2wMR = 0.97), but smaller in T1w MRI (GTVT1wMR = 0.76), suggesting possible peripheral edema around the tumor. Average GTV variation within the breathing cycle (22%) in 4DMRI is slightly greater than 4DCT (17%). GTV motion variation (−4 to 12 mm) and ITV variation (∆VITV=−25 to 95%) between 4DCT and 4DMRI are large, confirmed by relatively low ITV similarity (Dice = 0.72 ± 0.11) and large MDA = 2.9 ± 1.5 mm. Conclusion Average GTVs are similar between T2w‐4DMRI and 4DCT, but smaller by 25% in T1w BH MRI. Physician training and breathing coaching may be necessary to reduce ITV variability between 4DMRI and 4DCT. Four‐dimensional magnetic resonance imaging is a promising and viable technique for clinical lung tumor delineation and motion assessment.

A modern review of the uncertainties in volumetric imaging of respiratory‐induced target motion in lung radiotherapy

“…102,212 Multiple studies have demonstrated the advantage of using extended cine MRI to identify greater variability in target motion ranges, thereby better informing the delineation of the ITV to incorporate these variations, as compared to 4D-CT imaging alone. 96,204,213,214 MIP-based ITVs from 4D-MRI were demonstrated to be feasible and comparable to those typically generated from 4D-CT. 215 In order to further validate the feasibility of using 4D-MRI for ITV delineation, Zhang et al 216 did a comparison study involving 6 radiation oncologists contouring on four different lung cancer patients with a total of 16 lesions of various sizes and at different (central vs. peripheral) locations on T2 4D-MRI, T1 BH MRI, and 4D-CT scans. The physicians contoured gross tumor volumes (GTVs) and the ITV was taken as the composite of the GTVs, without any additional margin.…”

“…In order to further validate the feasibility of using 4D‐MRI for ITV delineation, Zhang et al 216 did a comparison study involving 6 radiation oncologists contouring on four different lung cancer patients with a total of 16 lesions of various sizes and at different (central vs. peripheral) locations on T2 4D‐MRI, T1 BH MRI, and 4D‐CT scans. The physicians contoured gross tumor volumes (GTVs) and the ITV was taken as the composite of the GTVs, without any additional margin.…”

Definition of internal target volumes based on planar X‐ray fluoroscopic images for lung and hepatic stereotactic body radiation therapy. Comparison to inhale/exhale CT technique

“…4DCT technique presents some shortcomings when compared to other methods like FI 12 or 4DMRI. [13][14][15] For example, 4DCT cannot detect inter-and intrafractional variations in the breathing pattern, which produces an insufficient representation of tumor movement. In addition, its high cost makes few departments have installed this type of equipment and its implementation is still limited even in developed countries.…”

Respiratory-Correlated (RC) vs. Time-Resolved (TR) Four-Dimensional Magnetic Resonance Imaging (4DMRI) for Radiotherapy of Thoracic and Abdominal Cancer

“…So far, the image resolution is approaching or exceeding that of 4DCT, while the binning artifacts have been substantially reduced or virtually eliminated and scanning time has become clinically acceptable. With the advantages of soft-tissue contrast enhancement and elimination of ionizing radiation, RC-4DMRI technique has been increasingly tested in the clinic and have the potential to play a role in clinical applications (10, 11, 28, 29). However, RC-4DMRI shares the same limitation of one breathing cycle as 4DCT, while using a snapshot of patient respiration as the average motion has been questioned for its validity and reliability (30–32).…”

“…The DIR-propagated contours were found as good as human contours owing to the high soft-tissue contrasts in T2w 4DMRI. Zhang et al also reported lung tumor delineation in 10 patients from 6 radiation oncologists and compared the results with those from 4DCT and T1w breath-hold images (29). All images were acquired on the simulation day within 2 h. It was found that T2w RC-4DMRI produced a similar GTV to 4DCT but with a much smaller variation among physicians, while T1w MRI based GTV is about 25% smaller.…”