Author: Raghavendiran Boopathy, Mansoor Khan, Srinidhi Rajagopalan 👨🔬
Affiliation: University of Oklahoma, University of Oklahoma Health Sciences Center 🌍
Purpose: This study aims to evaluate and compare the dosimetric outcomes of spatially fractionated radiotherapy (SFRT) grid planning techniques using Varian Eclipse for a Varian Edge C-arm LINAC system and Accuray Precision for TomoTherapy Radixact.
Methods: Five patients were included in the study in which three of them were pelvis and two lung patients The same planning clinical goals/constraints were used for both planning optimizations. The tumor size ranges from 255 cc to 3785 cc. Spherical Grids with a diameter of 1.5 cm were contoured within the gross tumor volume (GTV), spaced 3 cm center-to-center, and cropped to remain at least 2 cm from any organs at risk (OARs). Grid treatment plans were created using Varian Eclipse (version 16.0) for the Varian Edge c-arm Linac and Accuray Precision (version 3.5.0.3) for the Radixact TomoTherapy. All eclipse plans were created with two full arcs.
Results: The plans were compared for target coverage, mean dose to target, conformity Index, Gradient index, and OAR dose. The average mean dose to target were 98.4 and 99.43 with standard deviation of 0.25 and 0.28 for Edge machine and Radixact respectively. Both plans gave comparable conformity index. The average gradient measure were 2.4 and 2.8 with a standard deviation of 0.63 and 0.68 for Edge and TomoTherapy plans. For one patient where the tumor was 3785 cc both plans struggled with dose fall off index. But Edge machine showed better fall off primarily due to the MLC size.
Conclusion: Both delivery systems were capable of delivering comparable quality treatment plans. Users are cautioned for tumor larger than 2000 cc or number of grids more than 50 which may produce undesirable dose fall off.