Risk estimation of radiation induced second cancers for three dimensional conformal radiotherapy (3D-CRT) and intensity modulated radiotherapy (IMRT)

Abstract

The main purpose of this study was to determine and evaluate the organ equivalent dose (OED) used for the calculation of second cancer risk in prostate cancer patients treated with 10 MV photon, either using three-dimensional conformal radiotherapy (3D-CRT) or intensity modulated radiotherapy (IMRT) technique. Both 3D-CRT and IMRT plans were optimized for each of the 10 patients using Eclipse Radiation Therapy Planning System (RTPS), from which the differential dose volume histograms (dDVHs) for organs of interest were extracted. The three-dimensional dose distribution data were used for calculation of the primary beam OED. The scatter dose was measured by thermoluminescence dosimeters 700 (TLD700 rods) using an Alderson Rando phantom to simulate the treatment condition according to 3D-CRT and IMRT plans. IMRT plan induced a significant 2-fold increase in scatter component of OED compared with 3D-CRT (p = 0.009) and a 1.13 fold reduction in primary beam component (p = 0.0001). When the primary and scatter components were combined, the total OEDs for IMRT and 3D-CRT were 0.41 and 0.43 Gy, respectively. No significant difference could be observed (p = 0.185). On average, risk of the second cancer from IMRT and 3D-CRT plans was 12.47 risks/10,000 patients/year. In conclusion, IMRT plan does not induce greater second cancer risk than 3D-CRT. The average OED for these plans was 0.42 Gy.