An interactive plan and model evolution method for knowledge-based pelvic VMAT planning.

PURPOSE

To test if a RapidPlan DVH estimation model and its training plans can be improved interactively through a closed-loop evolution process.

METHODS AND MATERIALS

Eighty-one manual plans (P ) that were used to configure an initial rectal RapidPlan model (M ) were reoptimized using M (closed-loop), yielding 81 P plans. The 75 improved P (P ) and the remaining 6 P were used to configure model M . The 81 training plans were reoptimized again using M , producing 23 P plans that were superior to both their P and P forms (P ). Hence, the knowledge base of model M composed of 6 P , 52 P , and 23 P . Models were tested dosimetrically on 30 VMAT validation cases (P ) that were not used for training, yielding P (M ), P (M ), and P (M ) respectively. The 30 P were also optimized by M as trained by the library of M and 30 P (M ).

RESULTS

Based on comparable target dose coverage, the first closed-loop reoptimization significantly (P < 0.01) reduced the 81 training plans' mean dose to femoral head, urinary bladder, and small bowel by 2.65 Gy/15.63%, 2.06 Gy/8.11%, and 1.47 Gy/6.31% respectively, which were further reduced significantly (P < 0.01) in the second closed-loop reoptimization by 0.04 Gy/0.28%, 0.18 Gy/0.77%, 0.22 Gy/1.01% respectively. However, open-loop VMAT validations displayed more complex and intertwined plan quality changes: mean dose to urinary bladder and small bowel decreased monotonically using M (by 0.34 Gy/1.47%, 0.25 Gy/1.13%) and M (by 0.36 Gy/1.56%, 0.30 Gy/1.36%) than using M . However, mean dose to femoral head increased by 0.81 Gy/6.64% (M ) and 0.91 Gy/7.46% (M ) than using M . The overfitting problem was relieved by applying model M .

CONCLUSIONS

The RapidPlan model and its constituent plans can improve each other interactively through a closed-loop evolution process. Incorporating new patients into the original training library can improve the RapidPlan model and the upcoming plans interactively.