Author: M. Victoria Duran, María Fernández, Inés Flores, Joaquin Hernandez, Nuria Montero, Rodrigo Plaza, Manuel Ruiz, Francisco San Miguel, Sandra Williamson Puente, Zigor Zalabarria 👨🔬
Affiliation: Hospital Central de la Defensa 'Gómez Ulla', Hospital Central de la Defensa "Gomez Ulla", CSVE, Hospital Central de la Defensa 'Gómez Ulla', CSVE 🌍
Purpose:
Contouring guides recommend using para-axial, para-sagittal and para-coronal axis for delimitation of ROIs. These axis are rotated from the standard axis to match the anatomy of the patient (typically vaginal canal or uterus). Brachytherapy TPS typically allow for these axis to be used for contouring, but the same does not apply to external radiotherapy TPS (such as Monaco).
Methods:
We have devised a method that allows us to contour ROIs (and apply non-istropic expansions) in Monaco by using an auxiliary second series of images (series A) that has to be co-registered to the images intended for contouring and planning (series B).
We load series A as the main image series in Monaco while series B is loaded as secondary. While visualizing only series B, we rotate it in the Fusion module so that the vertical axis in the Sagittal view is parallel to the anatomical region of interest. We then contour any ROI requiring para-axial contouring in the Planning module. These structures are being generated onto series A while being visualized in series B. Expansions can be applied non-isotropically, following these rotated axis. We then copy the structures to series B, where they will follow the anatomy of the patient.
After clean-up (resetting the transformation matrix and removal of any ROIs in the auxiliary series A), these structures are ready for planning or exporting to other TPS (e.g., Oncentra).
Results:
This method allows us to contour ROIs following the anatomy of the patient and preserving the cylindrical symmetry typical of brachytherapy planning. Thus, we guarantee a better delineation of the regions to be irradiated, reducing the dose to healthy tissue due to misalignment between axis and anatomy.
Conclusion:
We have developed a method that allows para-axial contouring in Monaco, improving the ability of the physicians to precisely delineate structures.