Purpose
To determine under what conditions PET imaging will be useful in decisions regarding the use of radiation therapy for the treatment of clinically-occult lymph node metastases in head and neck cancer.
Methods and Materials
A decision model of PET imaging and its downstream effects on radiation therapy outcomes was constructed using an influence diagram. This model included the sensitivity and specificity of PET as well as the type and stage of the primary tumor. These parameters were varied to determine the optimal strategy for imaging and therapy for different clinical situations. Maximum Expected Utility was the metric by which different actions were ranked.
Results
For primary tumors with a low probability of lymph node metastases, the sensitivity of PET should be maximized and 50 Gy should be delivered if PET is positive and 0 Gy if negative. As the probability for lymph node metastases increases, PET imaging becomes unnecessary in some situation and the optimal dose to the lymph nodes increases. The model needed to include the causes of certain health states in order to predict current clinical practice.
Conclusion
The model demonstrated the ability to reproduce expected outcomes for a range of tumors and provided recommendations for different clinical situations. The differences between the optimal policies and current clinical practice is likely due to a disparity between stated clinical decision processes and actual decision making by clinicians.