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Virtual modelling of novel applicator prototypes for cervical cancer brachytherapy

View Article: PubMed Central - PubMed

ABSTRACT

Background: Standard applicators for cervical cancer Brachytherapy (BT) do not always achieve acceptable balance between target volume and normal tissue irradiation. We aimed to develop an innovative method of Target-volume Density Mapping (TDM) for modelling of novel applicator prototypes with optimal coverage characteristics. Patients and methods. Development of Contour-Analysis Tool 2 (CAT-2) software for TDM generation was the core priority of our task group. Main requests regarding software functionalities were formulated and guided the coding process. Software validation and accuracy check was performed using phantom objects. Concepts and terms for standardized workflow of TDM post-processing and applicator development were introduced.

Results: CAT-2 enables applicator-based co-registration of Digital Imaging and Communications in Medicine (DICOM) structures from a sample of cases, generating a TDM with pooled contours in applicator-eye-view. Each TDM voxel is assigned a value, corresponding to the number of target contours encompassing that voxel. Values are converted to grey levels and transformed to DICOM image, which is transported to the treatment planning system. Iso-density contours (IDC) are generated as lines, connecting voxels with same grey levels. Residual Volume at Risk (RVR) is created for each IDC as potential volume that could contain organs at risk. Finally, standard and prototype applicators are applied on the TDM and virtual dose planning is performed. Dose volume histogram (DVH) parameters are recorded for individual IDC and RVR delineations and characteristic curves generated. Optimal applicator configuration is determined in an iterative manner based on comparison of characteristic curves, virtual implant complexities and isodose distributions.

Conclusions: Using the TDM approach, virtual applicator prototypes capable of conformal coverage of any target volume, can be modelled. Further systematic assessment, including studies on clinical feasibility, safety and effectiveness are needed before routine use of novel prototypes can be considered.

No MeSH data available.


Related in: MedlinePlus

Principles of Target-volume Density Map (TDM) generation and postprocessing on an example of 6 cervical cancer cases. (A) Contours of high risk clinical target volumes (CTVHR – thin white lines) are shown on mid-coronal T2 weighted MRI with the applicator in place. Source channels are depicted as thick white lines. (B) CAT 2 generates the TDM by rigid co-registration of individual CTVHRs on a reference applicator. TDM voxels are assigned target density values, corresponding to the number of encompassing CTVHRs. These values are transformed to grey levels. (C) Resulting TDM DICOM image is exported to treatment planning system where isodensity contours (IDC) are auto-segmented (white dotted lines).
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j_raon-2016-0048_fig_001: Principles of Target-volume Density Map (TDM) generation and postprocessing on an example of 6 cervical cancer cases. (A) Contours of high risk clinical target volumes (CTVHR – thin white lines) are shown on mid-coronal T2 weighted MRI with the applicator in place. Source channels are depicted as thick white lines. (B) CAT 2 generates the TDM by rigid co-registration of individual CTVHRs on a reference applicator. TDM voxels are assigned target density values, corresponding to the number of encompassing CTVHRs. These values are transformed to grey levels. (C) Resulting TDM DICOM image is exported to treatment planning system where isodensity contours (IDC) are auto-segmented (white dotted lines).

Mentions: Dedicated software (Contour Analysis Tool 2 – CAT 2) was developed by the task group. The principles of CAT 2 application are outlined in Figure 1. The method is based on sequential import of DICOM structure files from a representative sample of individual cases, containing the target volume and the tandem & ring applicator. CAT 2 performs rigid co-registration of the imported structures, based on the applicator as the frame of reference. This implies rotational and translational shifts of the target volume and the applicator, resulting in alignment of the (1) centre of the ring, (2) tandem and ring axes and (3) axis connecting the centre of the ring with the first ring-source position. Consequently, TDM is created as a hybrid data set, containing pooled information from a sample of cases. Individual target volumes in the TDM are aligned to the single reference applicator, maintaining unchanged relative topography to the applicator axes as in the original data set. The differences in tandem length and ring diameter are not taken into account during co-registration process. Each voxel of the TDM is assigned a Target Density Value (TDV), corresponding to the number of target volume contours that encompass that voxel. Finally, TDVs are converted to grey levels and the data set is transformed to DICOM image, containing the reference applicator and the TDM in an “applicator-eye-view”.


Virtual modelling of novel applicator prototypes for cervical cancer brachytherapy
Principles of Target-volume Density Map (TDM) generation and postprocessing on an example of 6 cervical cancer cases. (A) Contours of high risk clinical target volumes (CTVHR – thin white lines) are shown on mid-coronal T2 weighted MRI with the applicator in place. Source channels are depicted as thick white lines. (B) CAT 2 generates the TDM by rigid co-registration of individual CTVHRs on a reference applicator. TDM voxels are assigned target density values, corresponding to the number of encompassing CTVHRs. These values are transformed to grey levels. (C) Resulting TDM DICOM image is exported to treatment planning system where isodensity contours (IDC) are auto-segmented (white dotted lines).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5120583&req=5

j_raon-2016-0048_fig_001: Principles of Target-volume Density Map (TDM) generation and postprocessing on an example of 6 cervical cancer cases. (A) Contours of high risk clinical target volumes (CTVHR – thin white lines) are shown on mid-coronal T2 weighted MRI with the applicator in place. Source channels are depicted as thick white lines. (B) CAT 2 generates the TDM by rigid co-registration of individual CTVHRs on a reference applicator. TDM voxels are assigned target density values, corresponding to the number of encompassing CTVHRs. These values are transformed to grey levels. (C) Resulting TDM DICOM image is exported to treatment planning system where isodensity contours (IDC) are auto-segmented (white dotted lines).
Mentions: Dedicated software (Contour Analysis Tool 2 – CAT 2) was developed by the task group. The principles of CAT 2 application are outlined in Figure 1. The method is based on sequential import of DICOM structure files from a representative sample of individual cases, containing the target volume and the tandem & ring applicator. CAT 2 performs rigid co-registration of the imported structures, based on the applicator as the frame of reference. This implies rotational and translational shifts of the target volume and the applicator, resulting in alignment of the (1) centre of the ring, (2) tandem and ring axes and (3) axis connecting the centre of the ring with the first ring-source position. Consequently, TDM is created as a hybrid data set, containing pooled information from a sample of cases. Individual target volumes in the TDM are aligned to the single reference applicator, maintaining unchanged relative topography to the applicator axes as in the original data set. The differences in tandem length and ring diameter are not taken into account during co-registration process. Each voxel of the TDM is assigned a Target Density Value (TDV), corresponding to the number of target volume contours that encompass that voxel. Finally, TDVs are converted to grey levels and the data set is transformed to DICOM image, containing the reference applicator and the TDM in an “applicator-eye-view”.

View Article: PubMed Central - PubMed

ABSTRACT

Background: Standard applicators for cervical cancer Brachytherapy (BT) do not always achieve acceptable balance between target volume and normal tissue irradiation. We aimed to develop an innovative method of Target-volume Density Mapping (TDM) for modelling of novel applicator prototypes with optimal coverage characteristics. Patients and methods. Development of Contour-Analysis Tool 2 (CAT-2) software for TDM generation was the core priority of our task group. Main requests regarding software functionalities were formulated and guided the coding process. Software validation and accuracy check was performed using phantom objects. Concepts and terms for standardized workflow of TDM post-processing and applicator development were introduced.

Results: CAT-2 enables applicator-based co-registration of Digital Imaging and Communications in Medicine (DICOM) structures from a sample of cases, generating a TDM with pooled contours in applicator-eye-view. Each TDM voxel is assigned a value, corresponding to the number of target contours encompassing that voxel. Values are converted to grey levels and transformed to DICOM image, which is transported to the treatment planning system. Iso-density contours (IDC) are generated as lines, connecting voxels with same grey levels. Residual Volume at Risk (RVR) is created for each IDC as potential volume that could contain organs at risk. Finally, standard and prototype applicators are applied on the TDM and virtual dose planning is performed. Dose volume histogram (DVH) parameters are recorded for individual IDC and RVR delineations and characteristic curves generated. Optimal applicator configuration is determined in an iterative manner based on comparison of characteristic curves, virtual implant complexities and isodose distributions.

Conclusions: Using the TDM approach, virtual applicator prototypes capable of conformal coverage of any target volume, can be modelled. Further systematic assessment, including studies on clinical feasibility, safety and effectiveness are needed before routine use of novel prototypes can be considered.

No MeSH data available.


Related in: MedlinePlus