Research On Three-dimensional Dose Reconstruction Method For Dose Guided Radiotherapy

The3D dose reconstruction method plays a fundamental role in the implementation of Dose-guided radiotherapy (DGRT), which is considered to be an advanced technique for accurate radiotherapy. However, it hasn’t been broadly used due to the limitations including long computation time and low accuracy that cannot meet the requirements for the clinical practice. This study was mainly about key issues of the3D dose reconstruction methods involved in dose guided radiotherapy to solve the present problem and improve the practical utilization of DGRT being implemented in the clinical practice.Firstly, a systematic research has been done on the dose calibration of an amorphous-silicon Electronic Portal Imaging Device(aSi-EPID). According to the response characteristic of EPID, a fast dose calibration method was developed based on corrected parameters including artifacts effect, field size, phantom thickness and off-axis position. The method showed an average accuracy within1.5%of the dose calibration in millisecond to complete the conversion from the EPID image to the value of dose, which provides the basic input for the3D dose reconstruction.Secondly, based on the previously dose reconstruction model developed by our group, a fast3D dose reconstruction algorithm was proposed combining Monte Carlo Finite Pencil Beam (MCFSPB) combined with a fast iteration algorithm. By testing on both the regular beams and clinical IMRT cases, it can reduce the reconstruction time to3-4s with a speed-up around50times faster than the original method, which greatly improved the practical utilization of implementing this dose reconstruction method into clinical practice.Finally, a direct back-projection dose reconstruction method was developed to make the reconstruction less dependent on dose calculation engine and dose calibration method in order to enhance the accuracy and robustness of reconstruction on the heterogeneous phantoms(e.g. human beings). By the distribution measurement of the intensity of the original beam going through the phantom using EPID, the incident fluence of the beam before the phantom can be calculated with the backprojection method. A large number of experiments have been carried out to acquire the measurement data and the scattering kernels under different phantom thickness and off-axis position were considered during the calculation. Lots of experimentals have been done on the homogeneous phantom, anthropomorphic human phantom with clinical IMRT patient cases. The results showed good satisfaction both on accuracy and speed for the clinical scenarios, laying great foundations for the clinical implementation of dose guided radiotherapy.