Abstract:
Objective Based on intensity modulated radiation therapy(IMRT) phantom, the impact of CT-to-density conversion curve on dosimetry verification of IMRT is investigated and calibrated.
Methods The electron density phantom was used to establish the CT-to-density conversion curve in radiation treatment planning system. IMRT plans of 12 nasopharynx carcinoma patients were chosen, copied to IMRT phantom and computed for the dose distribution. For each plan a measured point was put at the place where the dose was well-distributed and its dose value was measured using the ionization chamber. The physical density of IMRT phantom and its CT value were input into the planning system, to make a calibration for the CT-to-density conversion curve. The dose distribution was recomputed for each IMRT plan. Other parameters were kept the same in the plans and the differences between the computed dose values before and after correction were compared with the measured values.
Results In 12 nasopharynx carcinoma IMRT plans, the average error of computed dose values was 1.96% ± 0.87% before correction and 0.63% ± 0.74% after correction, compared with measured values. The error between measured values and computed values after correction was less than ±2% whereas the maximum error of computed values before correction was 3.24%.
Conclusions The com-puted dose values are closer to the measured values when using the calibrated CT-to-density conversion curve. The CT density values of IMRT phantom should be verified before usage, so as to increase the accuracy of IMRT dosimetry verification.
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