Robust Optimization for IMPT: Introducing and Comparing Different Automated Approaches

Intensity-modulated proton therapy (IMPT) is a radiotherapy treatment modality that has proven to be able to properly irradiate tumors while preserving as much as possible normal tissues. However, it is extremely vulnerable to several different sources of uncertainties, which motivates the use of robust treatment planning optimization. In this work we describe a new approach for robust automated IMPT treatment optimization, based on a set of auxiliary structures that are shifted versions of each one of the volumes of interest (clinical target volume - CTV and organs-at-risk - OARs), and that are named clones. This approach is compared with the use of a pseudo-Planning Target Volume (PTV) and pseudo-planning OAR volumes built by the union of all the CTV and OAR clones, respectively. For proof-of-concept, the proposed methodologies were tested using five post-operative prostate cancer cases. The quality of the calculated treatment plans was assessed by Monte Carlo simulation. For IMPT treatment plan robust optimization, the new strategy based on the use of clones using shifts of 6 mm presented better results in terms of robustness when compared with the traditional PTV-based approach. Taking uncertainties into consideration during the planning process can be an option to overcome one of the major drawbacks of IMPT.