Feasibility of Image Registration and Intensity-Modulated Radiotherapy Planning With Hyperpolarized Helium-3 Magnetic Resonance Imaging for Non–Small-Cell Lung Cancer

Abstract

Purpose: To demonstrate the feasibility of registering hyperpolarized helium-3 magnetic resonance images (3He-MRI) to X-ray computed tomography (CT) for functionally weighted intensity-modulated radiotherapy (IMRT) planning.Methods and Materials: Six patients with non–small-cell lung cancer underwent 3He ventilation MRI, which was fused with radiotherapy planning CT using rigid registration. Registration accuracy was assessed using an overlap coefficient, calculated as the proportion of the segmented 3He-MR volume (VMRI) that intersects the segmented CT lung volume expressed as a percentage of VMRI. For each patient, an IMRT plan that minimized the volume of total lung receiving a dose ≥20 Gy (V20) was compared with a plan that minimized the V20 to well-ventilated lung defined by the registered 3He-MRI.Results: The 3He-MRI and CT were registered with sufficient accuracy to enable functionally guided IMRT planning (median overlap, 89%; range, 72–97%). In comparison with the total lung IMRT plans, IMRT constrained with 3He-MRI reduced the V20 not only for the well-ventilated lung (median reduction, 3.1%; range, 0.4–5.1%; p = 0.028) but also for the total lung volume (median reduction, 1.6%; range, 0.2–3.7%; p = 0.028).Conclusions: Statistically significant improvements to IMRT plans are possible using functional information provided by 3He-MRI that has been registered to radiotherapy planning CT.

Functional image-based radiotherapy planning for non-small cell lung cancer: A simulation study

“…Seven scenarios using simulated functional imaging data representing locally advanced NSCLC have demonstrated that inclusion of functional information in IMRT plan optimisation allowed improved avoidance of functional lung, as assessed by FV 20 and the MFLD, compared to anatomical IMRT alone. The median reduction in FV 20 of 2.7% demonstrated in this simulation study is in keeping with that observed previously by Ireland et al of 3.1% (range 0.4-5.1%) [18] when using 3 He-MRI data, although it is less than the 5-6% absolute median reductions in FV 20 observed in selected SPECT literature examining functional versus anatomical IMRT [12,13].…”

“…In addition to improvements in functional lung dose-volume parameters observed in this study, small improvements in total lung V 20 volumes were identified, which have also been found by previous groups investigating functional radiotherapy planning [12,18]. A possible explanation for this improvement in V 20 may be an increased degree of freedom allowed to the planning algorithm when only functional lung doses are constrained, permitting distribution of total lung dose into not only low-dose zones, but also zones of non-functional lung where the 20 Gy threshold has already been exceeded, due to calculation of cost functions in inverse planning via an "area under the curve" method.…”

“…3 He-MRI avoids the need for additional radiation exposure whilst providing ventilation distribution images comparable to nuclear medicine techniques, and can be co-registered with conventional CT for radiotherapy treatment planning [15,16,18]. Evaluation of lung ventilation has also been proposed through observation of changes in the pulmonary parenchyma across the respiratory cycle using 4D-CT [14].…”

“…Evaluation of lung ventilation has also been proposed through observation of changes in the pulmonary parenchyma across the respiratory cycle using 4D-CT [14]. Both 3 He-MRI and 4D-CT have been combined with IMRT planning, allowing reductions in FV 20 of between 1% and 3% in preliminary studies [14,18].…”

Functional Imaging: CT and MRI

“…It is possible to obtain a 3D volumetric dataset of the lungs using this technique (169), and several authors have shown the utility of this technique in normal volunteers, patients with asthma, emphysema (including alpha-1-antitrypsin deficiency; Figure 10A), cystic fibrosis ( Figure 10B) and lung cancer ( Figure 10C). (170)(171)(172)(173)(174)(175)(176)(177) There is homogeneous ventilation distribution in normal volunteers, although small ventilation defects are frequently seen. (170,(178)(179)(180) In smoking subjects with normal pulmonary function tests, ventilation defects are usually already detectable.…”