Key Issues Of Optimization In Intensity Modulated Proton Therapy

Because of many special physical feathers including Bragg peak, proton was implement in radiation therapy rapidly. Intensity modulated proton therapy, short for IMPT, using active scanning delivery methods, could accurately delivery most of dose to target and reducing the dose of normal issue. While designing IMPT plan, there were many problems which would reduce the radiotherapy plan delivery quality, such as a great deal of scanning spot, many low dose distribution spot, long scanning path. And, the biological effect was not considered in the traditional dose constrains and dose-volume constrains, the intensity modulated optimization based on equivalent uniform dose with biological effect been considered. Aimed at these problems, research was done in this study on the key problem of intensity modulated proton therapy including scanning spot optimization, plan delivery key parameter and optimized based equivalent uniform dose, in order to improve the radiotherapy.Firstly, a scanning spot optimization with scanning spot selection based on proton Bragg peak position was developed.In scanning spot selection method, the scanning spot was accurately selected which Bragg peak position was in target. Based on the scanning spot selection, the dose distribution was optimization using conjoint gradient method. In the method, the scanning spot was accurately selected and quickly optimized. At last, we select simulating case in TG-119 report by the AAPM and two clinical cases include head&neck and prostate to test the method. The result showed that the IMPT plan could be optimized in 10-20 minutes, and the dose distribution was better than the dose distribution of photon treatment plan. The scanning spot optimization method could meet the clinical requirement to improve the plan quality greatly!Secondly, a scan spot reducing optimization of using the exclusive method and zero-setting method and scanning path optimization based on the genetic algorithm was developed. The scan spot reducing optimization method could exclude the low dose distribution scan spot, set the low MU of scanning spot to zero and re-optimize. In the scan path optimization method, the minimum length of scan path problem would be converted to travel salesman problem and be optimized by the genetic method. All these methods were test in simulated case of TG-119 report and a clinical head & neck cases. The result showed that, without effect on the dose distribution, the method could reduce the scan spot to 50.75%, reducing the length of scanning path 53.15%, reducing the magnet runtime 15.98%, while the robustness and the delivery quality of the plan was improved.At last, an optimized method based on equivalent uniform dose was developed by modify the dose target. In this method, combining the stair-like constrains setting, the dose target of dose objective quadratic function was modified while optimizing to shape DVH and improve the optimization results, which optimization with dose and dose-volume constrains could not generally shape the DVH. All these methods were test in clinical head&neck and prostate cases. The result showed that max dose was reduced 1291.75 cGy, V50 was reduced to 66.39%, while the treatment plan was highly improving.After the research of the key problem of intensity modulated proton treatment plan optimization, the method developed in this thesis could quickly optimized intensity modulated proton treatment plan, improved the treatment plan delivery quality and made the treatment plan more practicability.