Room: ePoster Forums
Purpose: A voxel based method is proposed to evaluate the sequential radiotherapy treatment plans incorporating the fractionation correction strategy for different dose regimens.
Methods: A patient of carcinoma prostate was selected for this study. Radiotherapy treatment plans were made with the VMAT technique using Eclipse TPS version 11.0 (Varian Medical System, Palo Alto, CA, USA) for the demonstration of the proposed method. In the first phase, the prescribed dose of 52 Gy in 26 fractions to the PTV (CTV Prostate and Seminal Vesicles + 10 mm margin) and in the second phase, 19.5 Gy in 3 fractions to the PTV Boost (CTV prostate + 5 mm margin) were used to plan over the same CT dataset. In voxel based radiobiology display (VRb) tool, during conversion of physical doses into radiobiological doses, special emphasis was given to the CTV radiobiology where voxels of the CTV in both phases were assigned with Î±/Î² value of 1.4 Gy (for this case only) and rest of the voxels outside CTV were assigned with Î±/Î² value of 3 Gy. BED of voxels which have doses greater than threshold dose (=2 Ã— Î±/Î²) was calculated using the LQL model and BED of remaining voxels was calculated using the LQ model.
Results: (1) Physical dose, BED- and EQDâ‚‚-colorwash for the reconstructed plan sum have been overlaid on the same CT- and Structures-Cube. Physical dose, BED- and EQDâ‚‚-volume histograms have been reconstructed for the sequential plan. Maximum values of 74.4 Gy, 94.8 Gy, and 218.7 Gy were obtained for the physical dose, EQDâ‚‚ and BED Cubes respectively.
Conclusion: The proposed method is an extension of VRb tool. It provides physical and fractionation corrected radiobiological dose colorwash and dose volume based statistics for the contoured OARs and target volumes for the evaluation of radiotherapy sequential treatment plan.