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Comparison of 3D MRI with high sampling efficiency and 2D multiplanar MRI for contouring in cervix cancer brachytherapy.

Petric P, Hudej R, Rogelj P, Blas M, Segedin B, Logar HB, Dimopoulos JC - Radiol Oncol (2012)

Bottom Line: When averaged over all delineated slices, the distances between contours in the inter-approach analysis were 2.6 (Standard deviation (SD) 0.4) mm and 2.8 (0.7) mm for observers 1 and 2, respectively.The magnitude of topographic and volumetric inter-observer contouring uncertainties, as obtained on the conventional approach, was maintained on the test approach.This variation was comparable to the inter-approach uncertainties with distances between contours of 3.1 (SD 0.8) and 3.0 (SD 0.7) mm on conventional and test approach, respectively.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiotherapy, Institute of Oncology Ljubljana, Ljubljana, Slovenia.

ABSTRACT

Background: MRI sequences with short scanning times may improve accessibility of image guided adaptive brachytherapy (IGABT) of cervix cancer. We assessed the value of 3D MRI for contouring by comparing it to 2D multi-planar MRI.

Patients and methods: In 14 patients, 2D and 3D pelvic MRI were obtained at IGABT. High risk clinical target volume (HR CTV) was delineated by 2 experienced radiation oncologists, using the conventional (2D MRI-based) and test (3D MRI-based) approach. The value of 3D MRI for contouring was evaluated by using the inter-approach and inter-observer analysis of volumetric and topographic contouring uncertainties. To assess the magnitude of deviation from the conventional approach when using the test approach, the inter-approach analysis of contouring uncertainties was carried out for both observers. In addition, to assess reliability of 3D MRI for contouring, the impact of contouring approach on the magnitude of inter-observer delineation uncertainties was analysed.

Results: No approach- or observer - specific differences in HR CTV sizes, volume overlap, or distances between contours were identified. When averaged over all delineated slices, the distances between contours in the inter-approach analysis were 2.6 (Standard deviation (SD) 0.4) mm and 2.8 (0.7) mm for observers 1 and 2, respectively. The magnitude of topographic and volumetric inter-observer contouring uncertainties, as obtained on the conventional approach, was maintained on the test approach. This variation was comparable to the inter-approach uncertainties with distances between contours of 3.1 (SD 0.8) and 3.0 (SD 0.7) mm on conventional and test approach, respectively. Variation was most pronounced at caudal HR CTV levels in both approaches and observers.

Conclusions: 3D MRI could potentially replace multiplanar 2D MRI in cervix cancer IGABT, shortening the overall MRI scanning time and facilitating the contouring process, thus making this treatment method more widely employed.

No MeSH data available.


Related in: MedlinePlus

Post-insertion pelvic MRI. (A) Para-transverse 2D T2w FSE MR images were imported into the TPS (left). Para-sagittal and -coronal images were resampled from this data-set (right): due to the 3.9 mm slice thickness, their resolution is poor. (B) 3D MRI data-set was imported into the TPS. High resolution para-transverse (left), -sagittal and -coronal images (right) were resampled due to an isotropic voxel size of 1 mm. (C) Co-registration of the 2D para-transverse and 3D MRI data-sets.
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f1-rado-46-03-242: Post-insertion pelvic MRI. (A) Para-transverse 2D T2w FSE MR images were imported into the TPS (left). Para-sagittal and -coronal images were resampled from this data-set (right): due to the 3.9 mm slice thickness, their resolution is poor. (B) 3D MRI data-set was imported into the TPS. High resolution para-transverse (left), -sagittal and -coronal images (right) were resampled due to an isotropic voxel size of 1 mm. (C) Co-registration of the 2D para-transverse and 3D MRI data-sets.

Mentions: However, limited access to MRI precludes its widespread adoption in this field. Until the role of low cost modalities (CT and US) is systematically evaluated, implementation of high resolution MRI sequences with short scanning times may make IGABT available to a wider population of patients. Currently, assessment of multiplanar post-insertion 2D T2w FSE MRI is required for accurate contouring.1,2,27 However, majority of treatment planning systems (TPS) do not enable import of non-resampled images in multiple planes. Classically, only (para)transverse images are imported and used for delineation, while other planes are resampled by the TPS from the (para)transverse set. Due to the slice thickness of 3–5 mm, the resampled images have poor resolution and are not useful for evaluation of patho-anatomical structures (Figure 1A). Non-resampled high-resolution (para)sagittal and (para)coronal 2D MR images have to be obtained in addition. As a result, 2D multiplanar MRI is characterized by long scanning time and the need for a separate DICOM-viewer to integrate findings from different planes during contouring.1,2,27,28 This approach is currently used at the Institute of Oncology Ljubljana. In addition, a 3D T2w FSE sequence with high sampling efficiency, 1 mm isotropic voxel size and large field of view (SPACE) is obtained at our department (Figure 1B). 3D MRI is co-registered with 2D para-transverse images in the TPS to reduce applicator reconstruction uncertainties.31 Due to the small voxel size, high resolution images in multiple planes can be resampled by the TPS from the 3D data-set (Figure 1C).


Comparison of 3D MRI with high sampling efficiency and 2D multiplanar MRI for contouring in cervix cancer brachytherapy.

Petric P, Hudej R, Rogelj P, Blas M, Segedin B, Logar HB, Dimopoulos JC - Radiol Oncol (2012)

Post-insertion pelvic MRI. (A) Para-transverse 2D T2w FSE MR images were imported into the TPS (left). Para-sagittal and -coronal images were resampled from this data-set (right): due to the 3.9 mm slice thickness, their resolution is poor. (B) 3D MRI data-set was imported into the TPS. High resolution para-transverse (left), -sagittal and -coronal images (right) were resampled due to an isotropic voxel size of 1 mm. (C) Co-registration of the 2D para-transverse and 3D MRI data-sets.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3472953&req=5

f1-rado-46-03-242: Post-insertion pelvic MRI. (A) Para-transverse 2D T2w FSE MR images were imported into the TPS (left). Para-sagittal and -coronal images were resampled from this data-set (right): due to the 3.9 mm slice thickness, their resolution is poor. (B) 3D MRI data-set was imported into the TPS. High resolution para-transverse (left), -sagittal and -coronal images (right) were resampled due to an isotropic voxel size of 1 mm. (C) Co-registration of the 2D para-transverse and 3D MRI data-sets.
Mentions: However, limited access to MRI precludes its widespread adoption in this field. Until the role of low cost modalities (CT and US) is systematically evaluated, implementation of high resolution MRI sequences with short scanning times may make IGABT available to a wider population of patients. Currently, assessment of multiplanar post-insertion 2D T2w FSE MRI is required for accurate contouring.1,2,27 However, majority of treatment planning systems (TPS) do not enable import of non-resampled images in multiple planes. Classically, only (para)transverse images are imported and used for delineation, while other planes are resampled by the TPS from the (para)transverse set. Due to the slice thickness of 3–5 mm, the resampled images have poor resolution and are not useful for evaluation of patho-anatomical structures (Figure 1A). Non-resampled high-resolution (para)sagittal and (para)coronal 2D MR images have to be obtained in addition. As a result, 2D multiplanar MRI is characterized by long scanning time and the need for a separate DICOM-viewer to integrate findings from different planes during contouring.1,2,27,28 This approach is currently used at the Institute of Oncology Ljubljana. In addition, a 3D T2w FSE sequence with high sampling efficiency, 1 mm isotropic voxel size and large field of view (SPACE) is obtained at our department (Figure 1B). 3D MRI is co-registered with 2D para-transverse images in the TPS to reduce applicator reconstruction uncertainties.31 Due to the small voxel size, high resolution images in multiple planes can be resampled by the TPS from the 3D data-set (Figure 1C).

Bottom Line: When averaged over all delineated slices, the distances between contours in the inter-approach analysis were 2.6 (Standard deviation (SD) 0.4) mm and 2.8 (0.7) mm for observers 1 and 2, respectively.The magnitude of topographic and volumetric inter-observer contouring uncertainties, as obtained on the conventional approach, was maintained on the test approach.This variation was comparable to the inter-approach uncertainties with distances between contours of 3.1 (SD 0.8) and 3.0 (SD 0.7) mm on conventional and test approach, respectively.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiotherapy, Institute of Oncology Ljubljana, Ljubljana, Slovenia.

ABSTRACT

Background: MRI sequences with short scanning times may improve accessibility of image guided adaptive brachytherapy (IGABT) of cervix cancer. We assessed the value of 3D MRI for contouring by comparing it to 2D multi-planar MRI.

Patients and methods: In 14 patients, 2D and 3D pelvic MRI were obtained at IGABT. High risk clinical target volume (HR CTV) was delineated by 2 experienced radiation oncologists, using the conventional (2D MRI-based) and test (3D MRI-based) approach. The value of 3D MRI for contouring was evaluated by using the inter-approach and inter-observer analysis of volumetric and topographic contouring uncertainties. To assess the magnitude of deviation from the conventional approach when using the test approach, the inter-approach analysis of contouring uncertainties was carried out for both observers. In addition, to assess reliability of 3D MRI for contouring, the impact of contouring approach on the magnitude of inter-observer delineation uncertainties was analysed.

Results: No approach- or observer - specific differences in HR CTV sizes, volume overlap, or distances between contours were identified. When averaged over all delineated slices, the distances between contours in the inter-approach analysis were 2.6 (Standard deviation (SD) 0.4) mm and 2.8 (0.7) mm for observers 1 and 2, respectively. The magnitude of topographic and volumetric inter-observer contouring uncertainties, as obtained on the conventional approach, was maintained on the test approach. This variation was comparable to the inter-approach uncertainties with distances between contours of 3.1 (SD 0.8) and 3.0 (SD 0.7) mm on conventional and test approach, respectively. Variation was most pronounced at caudal HR CTV levels in both approaches and observers.

Conclusions: 3D MRI could potentially replace multiplanar 2D MRI in cervix cancer IGABT, shortening the overall MRI scanning time and facilitating the contouring process, thus making this treatment method more widely employed.

No MeSH data available.


Related in: MedlinePlus