Investigation on Performance Accuracy of Different Surrogates in Real Time Tumor Tracking at External Beam Radiotherapy

Abstract

Purpose: In external beam radiotherapy of dynamic tumors, several errors raise due to inter- and intra-fractional motions. In order to compensate these errors, signals obtained from different surrogates are used to infer with tumor motion as real time. Therefore, a comparative assessment may be worthwhile on the effect of different surrogates in tumor motion tracking.
Methods: The performance accuracy of three internal-external surrogates entitled: external markers, diaphragm movement and lung volume was done using 4 Dimensional Extended Cardiac-Torso (4D-XCAT) phantoms. Adaptive Neuro Fuzzy Inference System (ANFIS) model was implemented to correlate the motion of surrogates with several tumors located in liver and lung, separately. Finally, the Root Mean Square Error (RMSE) of ANFIS model outputs in tumor motion prediction of different surrogates was compared as metric tool.
Results- The average value of RMSE of lung and liver tumors were 0.4 mm, 0.6 mm and 0.8 mm for external markers, lung volume and diaphragm motion, respectively.
Conclusion- Among three investigated surrogates, the best performance belonged to external markers strategy, while optimum location of these markers determined using an input selection algorithm in this method.