An in silico comparison between margin-based and probabilistic target-planning approaches in head and neck cancer patients

Background and purpose: To apply target probabilistic planning (TPP) approach to intensity modulated radiotherapy (IMRT) plans for head and neck cancer (HNC) patients. Material and methods: Twenty plans of HNC patients were re-planned replacing the simultaneous integrated boost IMRT optimization objectives for minimum dose on the boost target and the elective volumes with research probabilistic objectives: the latter allow for explicit handling of systematic and random geometric uncertainties, enabling confidence level based probabilistic treatment planning. Monte-Carlo evaluations of geometrical errors were performed, with endpoints D98%, D2% and Dmean, calculated at a confidence level of 90%. The dose distribution was expanded outside the patient to prevent large bilateral elective treatment volumes ending up in air for probabilistic shifts. Results: TPP resulted in more regular isodoses and in reduced dose, on average, to organs at risk (OAR), up to more than 6 Gy, while maintaining target coverage and keeping the maximum dose to limiting structures within requirements. In particular, when the surrounding OARs overlap with the planning target volume (PTV) but not with the clinical target volume (CTV), better results were achieved. Conclusion: The TPP approach was evaluated in HNC patients, and proven to be an efficient tool for managing uncertainties.