Room: Karl Dean Ballroom A2
Purpose: To develop a software tool that can perform rapid secondary 3D dose verification for online adaptive radiotherapy on MR-Linac.
Methods: The modified Clarkson integration method was generalized to calculate 3D dose with consideration of the effect of a 1.5 T transverse magnetic field using the beam data from a MR-Linac. The broken azimuthal symmetry of dose scattering due to the existence of the magnetic field was repaired by shifting the profile center back to the beam central axis. The amount of shift was obtained by comparing the profiles for various open fields, with and without the magnetic field, at clinically-relevant depths. The algorithm was implemented in C# with parallelization by using the CUDA library for parallel computing on GPU. The parallelization pattern was carefully implemented for each individual calculation point and segment. Gamma analysis was utilized to compare the calculated 3D doses with those from treatment planning system for a series of rectangular fields and realistic step-and-shoot IMRT plans on cube and cylinder phantoms.
Results: The gamma passing rates were all above 97% for all the rectangular fields with field sizes ranging from 1Ã—1 to 15Ã—15 cm2 using the gamma acceptance of 4 mm and 4%. For the IMRT QA plans, the gamma passing rates ranged 95% - 99%. On a windows 7 PC with NVIDIA NVS 310 GPU (4 GB total), the calculation time for IMRT was ~210 s for 9261 calculation points, and can be reduced to ~17 s if 343 calculation points are required.
Conclusion: A software tool that can rapidly compute 3D doses considering the effect of transverse magnetic field is developed. The tool can be used to perform secondary independent 3D dose verification for online adaptive radiation therapy with MR-Linac.