Tuning structure to pull a hotspot
Contour the hotspot itself, then constrain it. Faster and more local than raising the global max-dose weight.
Built in·updated 2026-08-03
When the plan has a hotspot in a place you do not want it — outside the GTV, at the target edge, in an OAR overlap — threshold the isodose that bounds it into a structure and give that structure a max-dose objective just under where it currently sits.
Re-optimize, re-threshold, repeat. Two or three rounds usually settles it.
Why not just raise the max-dose weight. A global max-dose objective is applied everywhere in the target, so raising its weight flattens the whole distribution, and on a SABR plan the hot core inside the GTV is wanted. A tuning structure asks for the one thing you actually want: less dose here.
Where it goes wrong. The structure is only valid for the plan it was thresholded from. Re-threshold after every optimization, or you are constraining a shape the dose no longer has.
How to do it in
- Tuning VOI
- threshold at the isodose bounding the hotspot
- Max Dose
- 2–3 % below the current hotspot
- Weight
- moderate high weight here flattens the wanted core dose
Threshold the isodose that bounds the hotspot into a VOI, add it to the optimizer and give it a Max Dose just under where the hotspot currently sits.
Re-optimize, re-threshold, repeat. Two or three rounds usually settles it.
Re-threshold every round. The structure describes where the dose was; after a run it is a shape the dose no longer has, and constraining it wastes weight on empty space.