Beam angle selection in intensity modulated proton therapy treatment planning for prostate cancer

Intensity modulated proton therapy (IMPT) was recently introduced to clinical cancer treatment because of the unique physical properties of protons that can result in highly conformal dose distributions. However, in IMPT treatment planning, the impact of beam angle selection on plan quality is still under investigation due to limited clinical experiences. One important topic is to find out the relationship between beam angle configuration and plan quality robustness regarding to treatment delivery uncertainties. We used a worst-case approach to account for systematic uncertainties and errors of IMPT delivery in our optimization model. Various scenarios of dose contribution were generated as input. The model set the dose calculation constraints in the most conservative way so that the deviation between planned and delivered dose distribution could be diminished at most. A linear programming based local neighborhood search was used to find robust beam angles. We tested our method on three prostate cancer cases and quality treatment plans were demonstrated for all cases.