How much time do you spend contouring? Most clinics would agree that it’s a lengthy process. While it can be tedious, it is an extremely important step in the planning process. Our treatment plans are only as good as our contours. With the current format of optimization and evaluation, we rely completely on accurate segmentation.
Recognizing how important yet time consuming the contouring process can be, we want to share a few of our contouring tips and tricks that our team developed in the clinic. What tips and tricks do you typically use? We’d love to hear what you find to be most helpful in the clinic.
Contouring femur takes a long time in prostate planning, as most of the automated tools are unable to properly separate out the correct bony anatomy. However, it is possible to save time by exploiting the symmetry of the left and right femur by using the Transform Structure and Flip Horizontal tools in Eclipse. After completing contours on one Femur, copy and paste it over the empty contralateral Femur structure. Right click to select Transform Structure and click Flip Horizontally.
Lastly, left-click on the solid and dashed solid lines to shift and rotate the structure in all three viewing planes to reposition the structure over the femur. Minimal corrections should be needed in most cases. A similar technique may be used to save time for manual contours of the eyes, humeral heads, and kidneys.
Minimizing Dose Spill Outside of the PTV
For dose spill constraints, it is beneficial to create a ~1 cm rind surrounding your target to minimize high dose spill outside of the PTV. Use the Extract Wall contour tool with outer margin = 1.0 and inner margin = -0.1 to create a rind structure that can be pushed in the optimizer to minimize dose spill. The 1 mm space between the PTV and rind structure minimizes the chances that there will be a conflicting goal within the optimizer and allow you to maintain coverage while pushing any high dose outside of the target.
For subsequent runs, you may convert the 102-105% IDL to a structure and then crop that region from the PTV to minimize dose spilling from certain directions. Creating a 1-2 mm margin on the cropped structure and then re-cropping can ensure that the dose spill region does not simply get shifted slightly during the next optimization.
After each optimization, it is quick and easy to calculate the dose spill in ClearCheck after each run without having to spend any time converting isodose lines to contours and evaluating manually on the DVH.
Contouring Tips for Brain SRS
Controlling and evaluating the conformity index and dose fall-off for multiple lesion brain SRS planning can pose a significant challenge to planners. Ensuring quality and consistency for these cases becomes increasingly difficult and time consuming as the number of targets rises. ClearCheck can save considerable time by allowing the user to quickly evaluate the conformity and gradient indices of multiple targets simultaneously.
To streamline the evaluation process of these plans in ClearCheck, it is necessary to create unique evaluation structures with a consistent naming convention to match the templates in ClearCheck. By setting up your Eclipse Structure Templates with a numerical ID at the beginning of each target structure name, your structures will automatically be sorted to the top of the structure list. Each PTV should then be matched with a corresponding dose evaluation region structure created by adding a ~1 cm margin to the PTV (eg. zGI_1).
For adjacent targets where the overlap regions will intersect, the pencil tool can be used to divide these structures up into separate regions.
In the ClearCheck Template Manager window, these structures can be attached to each PTV using the “Select Structure in lieu of Body” checkbox and choosing the matching structure.
By using structure naming templates in Eclipse and matching these to your ClearCheck SRS constraint templates, full plan evaluation can be done within seconds after completing a plan!
Tangent Breast Evaluation
Traditional tangent breast planning rarely required the evaluation of DVH coverage. However, as planning systems became more sophisticated and protocols required consistency among these plans, it has become necessary to contour the breast tissue as a target for plan evaluation. Though the breast target can still be defined using external markers, wires, and anatomical landmarks, it can be difficult to translate these clinical definitions into a 3D contour. Evaluating plan consistency can be challenging, as beam arrangements vary greatly depending on anatomy and target region within the breast.
However, once the beam angles and blocking have been constructed, a consistent Breast PTV Eval structure can be easily done in Eclipse using the following steps:
1. In Eclipse External Beam Planning, calculate the open tangent beams normalized with 100% of the dose to the center of the breast.
2. In right window, right-click on choose Convert Isodose Level to Structure… Enter 50% and click OK.
3. Navigate to the Contouring Workspace, and Select the Margin for Structure Tool. Create an Inner Margin of 0.5cm from 50% Dose structure and apply it to itself.
4. Use the Crop Structure tool to remove lung and liver and limit evaluation region to Breast and Chest Wall tissue only.
This method for PTV_Eval generation is identical to the process that our EZFluence software uses to auto-generate Electronic Compensator and Field-In-Field plans. As a bonus for EZFluence users in Eclipse 15.1 and higher, this structure will automatically be written back into Eclipse by the script.
For more information regarding Eclipse Contouring, we find the websites below to be very helpful:Eclipse Contouring Tips and Tricks: https://dosepedia.com/contouring-tips-tricks
eContour - Interactive Contouring Website: http://econtour.org/ (free to use after signup)
RTOG Contouring Atlases: https://www.rtog.org/CoreLab/ContouringAtlases.aspx