Program Information
A Method to Evaluate Dosimetric Properties of SFGRT in Eclipse TPS
M Xu1*, J Wei2 , R Tobias1 , J Dick2 , S Crawford2 , J Swanson2 , M Pankuch1 , (1) Northwestern Medicine Cancer Center, Warrenville, IL, (2) Landauer Medical Physics, Glenwood, IL and Cancer Treatment Centers of America at Southeastern Regional Medical Center, Newnan, GA
Presentations
SU-F-T-436 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: The objective was to develop a method for dose distribution calculation of spatially-fractionated-GRID-radiotherapy (SFGRT) in Eclipse treatment-planning-system (TPS).
Methods: Patient treatment-plans with SFGRT for bulky tumors were generated in Varian Eclipse version11. A virtual structure based on the GRID pattern was created and registered to a patient CT image dataset. The virtual GRID structure was positioned on the iso-center level together with matching beam geometries to simulate a commercially available GRID block made of brass. This method overcame the difficulty in treatment-planning and dose-calculation due to the lack o- the option to insert a GRID block add-on in Eclipse TPS. The patient treatment-planning displayed GRID effects on the target, critical structures, and dose distribution. The dose calculations were compared to the measurement results in phantom.
Results: The GRID block structure was created to follow the beam divergence to the patient CT images. The inserted virtual GRID block made it possible to calculate the dose distributions and profiles at various depths in Eclipse. The virtual GRID block was added as an option to TPS. The 3D representation of the isodose distribution of the spatially-fractionated beam was generated in axial, coronal, and sagittal planes.
Physics of GRID can be different from that for fields shaped by regular blocks because the charge-particle-equilibrium cannot be guaranteed for small field openings. Output factor (OF) measurement was required to calculate the MU to deliver the prescribed dose. The calculated OF based on the virtual GRID agreed well with the measured OF in phantom.
Conclusion: The method to create the virtual GRID block has been proposed for the first time in Eclipse TPS. The dose-distributions, in-plane and cross-plane profiles in PTV can be displayed in 3D-space. The calculated OF’s based on the virtual GRID model compare well to the measured OF’s for SFGRT clinical use.
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