Spatial Comparison of CT-Based Surrogates of Lung Ventilation With Hyperpolarized Helium-3 and Xenon-129 Gas MRI in Patients Undergoing Radiation Therapy.

PURPOSE: To develop and apply an image acquisition and analysis strategy for spatial comparison of computed tomography (CT)-ventilation images with hyperpolarized gas magnetic resonance imaging (MRI). METHODS AND MATERIALS: Eleven lung cancer patients underwent xenon-129 (129Xe) and helium-3 (3He) ventilation MRI and coregistered proton (1H) anatomic MRI. Expiratory and inspiratory breath-hold CTs were used for deformable image registration and calculation of 3 CT-ventilation metrics: Hounsfield unit (CTHU), Jacobian (CTJac), and specific gas volume change (CTSGV). Inspiration CT and hyperpolarized gas ventilation MRI were registered via same-breath anatomic 1H-MRI. Voxel-wise Spearman correlation coefficients were calculated between each CT-ventilation image and its corresponding 3He-/129Xe-MRI, and for the mean values in regions of interest (ROIs) ranging from fine to coarse in-plane dimensions of 5 × 5, 10 × 10, 15 × 15, and 20 × 20, located within the lungs as defined by the same-breath 1H-MRI lung mask. Correlation of 3He and 129Xe-MRI was also assessed. RESULTS: Spatial correlation of CT-ventilation against 3He/129Xe-MRI increased with ROI size. For example, for CTHU, mean ± SD Spearman coefficients were 0.37 ± 0.19/0.33 ± 0.17 at the voxel-level and 0.52 ± 0.20/0.51 ± 0.18 for 20 × 20 ROIs, respectively. Correlations were stronger for CTHU than for CTJac or CTSGV. Correlation of 3He with 129Xe-MRI was consistently higher than either gas against CT-ventilation maps over all ROIs (P < .05). No significant differences were observed between CT-ventilation versus 3He-MRI and CT-ventilation versus 129Xe-MRI. CONCLUSION: Comparison of ventilation-related measures from CT and registered hyperpolarized gas MRI is feasible at a voxel level using a dedicated acquisition and analysis protocol. Moderate correlation between CT-ventilation and MRI exists at a regional level. Correlation between MRI and CT is significantly less than that between 3He and 129Xe-MRI, suggesting that CT-ventilation surrogate measures may not be measuring lung ventilation alone.

Immobilization and image-guidance methods for radiation therapy of limb extremity soft tissue sarcomas: Results of a multi-institutional survey.

Radiation therapy for limb-extremity soft tissue sarcoma (STS) requires accurate, reproducible dose delivery. However, patient positioning is challenging and there is a lack of existing guidelines to assist institutional standardization. Therefore, we conducted a multi-institutional international survey of STS immobilization, image guidance methods, and treatment protocols to investigate current practice. Seventy-three UK radiotherapy centers and 15 hospitals in 7 other countries completed a questionnaire on STS immobilization and image-guidance procedures. Specifically, the survey collated information on the current usage of immobilization equipment, including custom devices, patient setup tolerances, the use of written protocols, the modality and frequency of image guidance, the method of treatment, allocated treatment times, and the application of surgical clips. Multiple combinations of immobilization devices were reported. In the UK, 12%, 40%, 30%, 12%, and 5% use 1, 2, 3, 4, and 5 types of device for lower limb STS. Vacuum bag plus either foot or ankle support was most common (66%). Of 15 international centers, 27%, 60%, 7%, 0%, 7% use 1, 2, 3, 4, 5 devices, with vacuum bags (73%) and thermoplastic (47%) predominant, similar to UK values of 77% and 52%. For image guidance, in the UK, 37% use kV planar, 34% use MV planar, and 16% use cone-beam CT for the first 3 fractions and then weekly. Internationally, daily imaging was more prevalent with 33% using kV planar, 7% MV planar, and 40% cone-beam CT daily. Custom devices plus combinations of devices, along with 5- and 10-mm set-up tolerances, were most commonly reported. Less than half of centers have written treatment protocols. Conventional treatment is most common in the UK, with only 42% using conformal techniques. Treatment is allocated between 10 and 30 minutes. Twenty-six percent of UK centers and 53% of international centers use surgical clips. Across treatment centers, there is no consistent approach to STS immobilization, image-guidance methods, or treatment protocols assessed by this survey. A wide variety of immobilization devices and configurations are utilized, and the frequency and modality of imaging are similarly diverse. In the absence of guidelines, the creation of an online repository of example immobilization techniques could enable centers to compare a diversity of cases. The availability of a forum for viewing and discussing a range of cases could potentially lead to improved patient setup and reduce the time taken to devise an individual immobilization strategy.

Impact of field number and beam angle on functional image-guided lung cancer radiotherapy planning.

To investigate the effect of beam angles and field number on functionally-guided intensity modulated radiotherapy (IMRT) normal lung avoidance treatment plans that incorporate hyperpolarised helium-3 magnetic resonance imaging (3He MRI) ventilation data. Eight non-small cell lung cancer patients had pre-treatment 3He MRI that was registered to inspiration breath-hold radiotherapy planning computed tomography. IMRT plans that minimised the volume of total lung receiving ⩾20 Gy (V20) were compared with plans that minimised 3He MRI defined functional lung receiving ⩾20 Gy (fV20). Coplanar IMRT plans using 5-field manually optimised beam angles and 9-field equidistant plans were also evaluated. For each pair of plans, the Wilcoxon signed ranks test was used to compare fV20 and the percentage of planning target volume (PTV) receiving 90% of the prescription dose (PTV90). Incorporation of 3He MRI led to median reductions in fV20 of 1.3% (range: 0.2-9.3%; p = 0.04) and 0.2% (range: 0 to 4.1%; p = 0.012) for 5- and 9-field arrangements, respectively. There was no clinically significant difference in target coverage. Functionally-guided IMRT plans incorporating hyperpolarised 3He MRI information can reduce the dose received by ventilated lung without comprising PTV coverage. The effect was greater for optimised beam angles rather than uniformly spaced fields.

Detection of radiation-induced lung injury in non-small cell lung cancer patients using hyperpolarized helium-3 magnetic resonance imaging.

PURPOSE: To compare hyperpolarized helium-3 magnetic resonance imaging ((3)He-MRI) acquired from non-small cell lung cancer (NSCLC) patients before and after external beam radiotherapy (EBRT). METHODS AND MATERIALS: In an Ethics Committee-approved prospective study, five patients with histologically confirmed NSCLC gave written informed consent to undergo computed tomography (CT) and (3)He-MR ventilation imaging 1 week prior to and 3 months after radiotherapy. Images were registered to pre-treatment CT using anatomical landmark-based rigid registration to enable comparison. Emphysema was graded from examination of the CT. MRI-defined ventilation was calculated as the intersection of (3)He-MRI and CT lung volume as a percentage of the CT lung volume for the whole lung and regions of CT-defined pneumonitis. RESULTS: On pre-treatment images, there was a significant correlation between the degree of CT-defined emphysema and (3)He-MRI whole lung ventilation (Spearman's rho=0.90, p=0.04). After radiation therapy, pneumonitis was evident on CT for 3/5 patients. For these cases, (3)He-MRI ventilation was significantly reduced within the regions of pneumonitis (pre: 94.1±2.2%, post: 73.7±4.7%; matched pairs Student's t-test, p=0.02, mean difference=20.4%, 95% confidence interval 6.3-34.6%). CONCLUSIONS: This work demonstrates the feasibility of detecting ventilation changes between pre- and post-treatment using hyperpolarized helium-3 MRI for patients with NSCLC. Pre-treatment, the degree of emphysema and (3)He-MRI ventilation were correlated. For three cases of radiation pneumonitis, (3)He-MRI ventilation changes between pre- and post-treatment imaging were consistent with CT evidence of radiation-induced lung injury.

An image acquisition and registration strategy for the fusion of hyperpolarized helium-3 MRI and x-ray CT images of the lung.

The purpose of this ethics committee approved prospective study was to evaluate an image acquisition and registration protocol for hyperpolarized helium-3 magnetic resonance imaging ((3)He-MRI) and x-ray computed tomography. Nine patients with non-small cell lung cancer (NSCLC) gave written informed consent to undergo a free-breathing CT, an inspiration breath-hold CT and a 3D ventilation (3)He-MRI in CT position using an elliptical birdcage radiofrequency (RF) body coil. (3)He-MRI to CT image fusion was performed using a rigid registration algorithm which was assessed by two observers using anatomical landmarks and a percentage volume overlap coefficient. Registration of (3)He-MRI to breath-hold CT was more accurate than to free-breathing CT; overlap 82.9 +/- 4.2% versus 59.8 +/- 9.0% (p < 0.001) and mean landmark error 0.75 +/- 0.24 cm versus 1.25 +/- 0.60 cm (p = 0.002). Image registration is significantly improved by using an imaging protocol that enables both (3)He-MRI and CT to be acquired with similar breath holds and body position through the use of a birdcage (3)He-MRI body RF coil and an inspiration breath-hold CT. Fusion of (3)He-MRI to CT may be useful for the assessment of patients with lung diseases.