A track repeating algorithm for intensity modulated carbon ion therapy.

The fast dose calculator (FDC), a track repeating Monte Carlo (MC) algorithm was initially developed for proton therapy. The validation for proton therapy has been demonstrated in a previous work. In this work we presented the extension of FDC to the calculation of dose distributions for ions, particularly for carbon. Moreover the code algorithm is validated by comparing 3D dose distributions and dose volume histograms (DVH) calculated by FDC with Geant4. A total of 19 patients were employed, including three patients of prostate, five of brain, three of head and neck, four of lung and four of spine. We used a gamma-index technique to analyze dose distributions and we performed a dosimetric analysis for DVHs, a more direct and informative quantity for planning system assessment. The gamma-index passing rates of all patients discussed in this paper are above 90% with the criterion 1%/1 mm, above 98% with the criterion 2%/2 mm and over 99.9% with the criterion 3%/3 mm. The root mean square (RMS) of percent difference of dosimetric indices D-02, D-05, D-50, D-95 and D-98 are 0.75%, 0.70%, 0.79%, 0.83% and 0.76%. All the differences are within clinically accepted norms.