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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.


Schematic representation of applicator modelling based on our theoretical example of Target-volume Density Map (TDM). Above: Three virtual applicators are reconstructed on the TDM. Dose distribution is optimized based on a set of specific planning aims for the isodensity contours (IDC) and for residual volumes at risk (RVR). The optimized prescription isodoses for individual applicators are shown as thick dotted lines. (A) Standard intracavitary applicator: limited possibility for optimization. The planning aim is achieved for ≈70% IDC. (B) Combined intracavitary and interstitial applicator with parallel parametrial needles (Vienna-type): planning aim is achieved for ≈95% IDC. (C) Combined intracavitary and interstitial applicator with parallel and oblique parametrial needles: planning aim as achieved for ≈100 % IDC. (D) Characteristic curves for the IDC of the three applicator types. RVR curves are not shown. Shaded areas under characteristic curves represents IDC ranges in which certain applicator is able to achieve the planning aim. Arbitrary planning aim and applicator thresholds are marked by dotted lines.
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j_raon-2016-0048_fig_002: Schematic representation of applicator modelling based on our theoretical example of Target-volume Density Map (TDM). Above: Three virtual applicators are reconstructed on the TDM. Dose distribution is optimized based on a set of specific planning aims for the isodensity contours (IDC) and for residual volumes at risk (RVR). The optimized prescription isodoses for individual applicators are shown as thick dotted lines. (A) Standard intracavitary applicator: limited possibility for optimization. The planning aim is achieved for ≈70% IDC. (B) Combined intracavitary and interstitial applicator with parallel parametrial needles (Vienna-type): planning aim is achieved for ≈95% IDC. (C) Combined intracavitary and interstitial applicator with parallel and oblique parametrial needles: planning aim as achieved for ≈100 % IDC. (D) Characteristic curves for the IDC of the three applicator types. RVR curves are not shown. Shaded areas under characteristic curves represents IDC ranges in which certain applicator is able to achieve the planning aim. Arbitrary planning aim and applicator thresholds are marked by dotted lines.

Mentions: Conventional treatment plan, based on the IC applicator with standard loading and dose specification at Manchester point A is applied to the TDM (Figure 2A). Dose volume histogram (DVH) parameters are recorded for individual IDCTDVs and RVRTDVS. Recommended minimal set of DVH parameters for IDCTDV includes volume receiving the prescribed dose (V100) and dose received by the 90% and 98% (D90 and D98) of the IDCTDV volume. For RVRTDV, minimum doses received by 2 cm3 of the most irradiated RVRTDV (D2cc) are recorded. Characteristic curves for the IC applicator with standard loading are generated by plotting the DVH parameters against IDCTDV and RVRTDV levels (Figure 2D).Figure 2


Virtual modelling of novel applicator prototypes for cervical cancer brachytherapy
Schematic representation of applicator modelling based on our theoretical example of Target-volume Density Map (TDM). Above: Three virtual applicators are reconstructed on the TDM. Dose distribution is optimized based on a set of specific planning aims for the isodensity contours (IDC) and for residual volumes at risk (RVR). The optimized prescription isodoses for individual applicators are shown as thick dotted lines. (A) Standard intracavitary applicator: limited possibility for optimization. The planning aim is achieved for ≈70% IDC. (B) Combined intracavitary and interstitial applicator with parallel parametrial needles (Vienna-type): planning aim is achieved for ≈95% IDC. (C) Combined intracavitary and interstitial applicator with parallel and oblique parametrial needles: planning aim as achieved for ≈100 % IDC. (D) Characteristic curves for the IDC of the three applicator types. RVR curves are not shown. Shaded areas under characteristic curves represents IDC ranges in which certain applicator is able to achieve the planning aim. Arbitrary planning aim and applicator thresholds are marked by 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_002: Schematic representation of applicator modelling based on our theoretical example of Target-volume Density Map (TDM). Above: Three virtual applicators are reconstructed on the TDM. Dose distribution is optimized based on a set of specific planning aims for the isodensity contours (IDC) and for residual volumes at risk (RVR). The optimized prescription isodoses for individual applicators are shown as thick dotted lines. (A) Standard intracavitary applicator: limited possibility for optimization. The planning aim is achieved for ≈70% IDC. (B) Combined intracavitary and interstitial applicator with parallel parametrial needles (Vienna-type): planning aim is achieved for ≈95% IDC. (C) Combined intracavitary and interstitial applicator with parallel and oblique parametrial needles: planning aim as achieved for ≈100 % IDC. (D) Characteristic curves for the IDC of the three applicator types. RVR curves are not shown. Shaded areas under characteristic curves represents IDC ranges in which certain applicator is able to achieve the planning aim. Arbitrary planning aim and applicator thresholds are marked by dotted lines.
Mentions: Conventional treatment plan, based on the IC applicator with standard loading and dose specification at Manchester point A is applied to the TDM (Figure 2A). Dose volume histogram (DVH) parameters are recorded for individual IDCTDVs and RVRTDVS. Recommended minimal set of DVH parameters for IDCTDV includes volume receiving the prescribed dose (V100) and dose received by the 90% and 98% (D90 and D98) of the IDCTDV volume. For RVRTDV, minimum doses received by 2 cm3 of the most irradiated RVRTDV (D2cc) are recorded. Characteristic curves for the IC applicator with standard loading are generated by plotting the DVH parameters against IDCTDV and RVRTDV levels (Figure 2D).Figure 2

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.